He studied the DNA molecule to see if the child was related to the man.
It is evident that this is practicable if the number and kind of atoms contained in the molecule of a compound can be determined.
It is now agreed that the molecule of water contains two atoms of hydrogen and one of oxygen, so that the atomic weight of oxygen becomes 16, and similarly that the molecule of ammonia contains three atoms of hydrogen and one of nitrogen, and that consequently the atomic weight of nitrogen is 14.
The symbols of compounds become very concise, as the number of atoms of one kind in a molecule can be expressed by a sub-index.
It would be a serious business to draw a Daltonian diagram for such a molecule.
necessary to determine the specific gravities of the various gases referred to some one of them, say hydrogen; the numbers so obtained giving the weights of the molecules referred to that of the hydrogen molecule.
(formamide excepted) which are at first soluble in water, the solubility, however, decreasing as the carbon content of the molecule increases.
By the entrance of amino or hydroxyl groups into the molecule dyestuffs are formed.
The cadmium molecule, as shown by determinations of the density of its vapour, is monatomic. The metal unites with the majority of the heavy metals to form alloys; some of these, the so-called fusible alloys, find a useful application from the fact that they possess a low melting-point.
The decomposition of the complex molecule of the sugar liberates a certain amount of energy, as can be seen from the study of the fermentation set tig by yeast, which is a process of this kind, in that it is intensified by the absence of oxygen.
This salt, on standing, decomposes into barium dithionate, BaS206, and diethyl disulphide, (C2H5)2S2, which points to the presence of the SH group in the molecule.
A higher temperature decomposes this body into carbon dioxide and itaconic acid, C 5 H 6 0 4, which, again, by the expulsion of a molecule of water, yields citraconic anhydride, C 5 H 4 0 3.
(1) particles derived by limiting mechanical subdivision, the modern molecule, and (2) particles derived from the first class by chemical subdivision, i.e.
Additional evidence as to the structure of the molecule was discussed by Avogadro in 1811, and by Ampere in 1814.
He established the existence of molecules and atoms as we have defined above, and stated that the number of atoms in the molecule is generally 2, but may be 4, 8, &c. We cannot tell whether his choice of the powers of 2 is accident or design.
the weight contained in a molecule of hydrochloric acid, thus differing from Avogadro who chose the weight of a hydrogen molecule.
He defined structure " as the manner of the mutual linking of the atoms in the molecule," but denied that any such structure could give information as to the orientation of the atoms in space.
A molecule may be defined as the smallest part of a substance which can exist alone; an atom as the smallest part of a substance which can exist in combination.
The molecule of every compound must obviously contain at least two atoms, and generally the molecules of the elements are also polyatomic, the elements with monatomic molecules (at moderate temperatures) being mercury and the gases of the argon group. The laws of chemical combination are as follows: I.
Usually, when the symbols of the elements are written or printed with a figure to the right, it is understood that this indicates a molecule of the element, the symbol alone representing an atom.
We may suppose that in the formation of gaseous hydrochloric acid from gaseous chlorine and hydrogen, according to the equation H2 +C1 2 = HCI+HC1, a certain amount of energy is expended in separating the atoms of hydrogen in the hydrogen molecule, and the atoms of chlorine in the chlorine molecule, from each other; but that heat is developed by the combination of the hydrogen atoms with the chlorine atoms, and that, as more energy is developed by the union of the atoms of hydrogen and chlorine than is expended in separating the hydrogen atoms from each other and the chlorine atoms from one another, the result of the action of the two elements upon each other is the development of heat, - the amount finally developed in the reaction being the difference between that absorbed in decomposing the elementary molecules and that developed by the combination of the atoms of chlorine and hydrogen.
The oxychloride, bromides, and other compounds were subsequently discovered; here we need only notice Moissan's preparation of the trifluoride and Thorpe's discovery of the pentafluoride, a compound of especial note, for it volatilizes unchanged, giving a vapour of normal density and so demonstrating the stability of a pentavalent phosphorus compound (the pentachloride and pentabromide dissociate into a molecule of the halogen element and phosphorus trichoride).
The binary conception of compounds held by Berzelius received apparent support from the observations of Gay Lussac, in 1815, on the vapour densities of alcohol and ether, which pointed to the conclusion that these substances consisted of one molecule of water and one and two of ethylene respectively; and from Pierre Jean Robiquet and Jean Jacques Colin, showing, in 1816, that ethyl chloride (hydrochloric ether) could be regarded as a compound of ethylene and hydrochloric acid.
Another consequence of the doctrine of valency was that it permitted the graphic representation of the molecule.
By its aid the molecule is represented as a collection of atoms connected together by valencies in such a manner that the part played by each atom is represented;.
(methylene) groups and the molecule consists of a single chain; such hydrocarbons are referred to as being normal; (2) has a branch and contains the group; CH (methine) in which the free valencies are attached to carbon atoms; such hydrocarbons are termed secondary or iso-; (3) is characterized by a carbon atom linked directly to four other carbon atoms; such hydrocarbons are known as tertiary.
NH 2; secondary, R2: NH; and tertiary, R3: N; the oxamines, R 3 N :0, are closely related to the tertiary ammonias, which also unite with a molecule of alkyl iodide to form salts of quaternary ammonium bases, e.g.
Thus from the acid-amides, which we have seen to be closely related to the acids themselves, we obtain, by replacing the carbonyl oxygen by chlorine, the acidamido-chlorides, R CC1 2 NH 2, from which are derived the imido-chlorides, R CC1:NH, by loss of one molecule of hydrochloric acid.
The ringed structure of benzene, C 6 H 61 was first suggested in 1865 by August Kekule, who represented the molecule by six CH groups placed at the six angles of a regular hexagon, the sides of which denoted the valencies saturated by adjacent carbon atoms, the fourth valencies of each carbon atom being represented as saturated along alternate sides.
Although Kekule founded his famous benzene formula in 1865 on the assumptions that the six hydrogen atoms in benzene are equivalent and that the molecule is symmetrical, i.e.
From the fact that reduction products containing either one or two double linkages behave exactly as unsaturated aliphatic compounds, being readily reduced or oxidized, and combining with the halogen elements and haloid acids, it seems probable that in benzenoid compounds the fourth valencies are symmetrically distributed in such a manner as to induce a peculiar stability in the molecule.
These bands are due to molecular oscillations; Hartley suggests the carbon atoms to be rotating and forming alternately single and double linkages, the formation of three double links giving three bands, and of three single links another three; Baly and Collie, on the other hand, suggest the making and breaking of links between adjacent atoms, pointing out that there are seven combinations of one, two and three pairs of carbon atoms in the benzene molecule.
This configuration is, according to Sachse, more stable than any other form; no oscillation is possible, the molecule being only able to move as a whole.
149, p. 20) established the symmetry of the naphthalene nucleus, and showed that whichever half of the molecule be oxidized the same phthalic acid results.
Bamberger opposed Claus' formula on the following grounds: - The molecule of naphthalene is symmetrical, since 2.7 dioxynaphthalene is readily esterified by methyl iodide and sulphuric acid to a dimethyl ether; and no more than two mono-substitution derivatives are known.
The molecule is aromatic but not benzenoid; however, by the reduction of one half of the molecule, the other assumes a benzenoid character.
If s-naphthylamine and 0-naphthol be reduced, tetrahydro products are obtained in which the aminoor oxy-bearing half of the molecule becomes aliphatic in character.
If a-naphthylamine and a-naphthol be reduced, the hydrogen atoms attach themselves to the non-substituted half of the molecule, and the compounds so obtained resemble aminodiethylbenzene, C 6 H 3 NH 2 (C 2 H 5) 21 and oxydiethylbenzene, C 6 H 3.
Bamberger's observations on reduced quinoline derivatives point to the same conclusion, that condensed nuclei are not benzenoid, but possess an individual character, which breaks down, however, when the molecule is reduced.
The formula has the advantage that it may be constructed from tetrahedral models of the carbon atom; but it involves the assumption that the molecule has within it a mechanism, equivalent in a measure to a system of railway points, which can readily close up and pass into that characteristic of benzene.
According to Armstrong, anthracene behaves unsymmetrically towards substituents, and hence one lateral ring differs from the other; he represents the molecule as consisting of one centric ring, the remaining medial and lateral ring being ethenoid.
Bamberger, on the other hand, extends his views on benzene and naphthalene and assumes the molecule to be (1).
(7) (2) Phenanthrene is regarded by Armstrong as represented by (3), the lateral rings being benzenoid, and the medial ring fatty; Bamberger, however, regards it as (4), the molecule being (3) (4) entirely aromatic. An interesting observation by Baeyer, viz.
For the complete determination of the chemical structure of any compound, three sets of data are necessary: (I) the empirical chemical composition of the molecule; (2) the constitution, i.e.
the manner in which the atoms are linked together; and (3) the configuration of the molecule, i.e.
The second and third sets elucidate the actual structure of the molecule: these are known as " constitutional properties."
We may therefore conclude that the molecular volume depends more upon the internal structure of the molecule than its empirical content.
Schroeder the silver salts of the fatty acids exhibit additive relations; an increase in the molecule of CH2 causes an increase in the molecular volume of about 15'3.
456) has given the formula Cp=6.5--aT, where a is a constant depending on the complexity of the molecule, as an expression for the molecular heat at constant pressure at any temperature T (reckoned on the absolute scale).
For a further discussion of the ratio of the specific heats see Molecule.
185.8° Equal increments in the molecule are associated with an equal rise in the boiling-point, but this increment varies in different homologous series.
While certain additive relations hold between some homologous series, yet differences occur which must be referred to the constitution of the molecule.
The introduction of negative groups into a molecule alters the boiling-point according to the number of negative groups already present.
A factor of considerable importance in determining boiling-points of isomers is the symmetry of the molecule.
Mag., 18 93 [5), 35, p. 45 8) has shown that, while an increase in molecular weight is generally associated with a rise in the boiling-point, yet the symmetry of the resulting molecule may exert such a lowering effect that the final result is a diminution in the boiling-point.
The series H 2 S = - 61°, CH 3 SH = 21 °, (C 11 3) 2 S=41 ° is an example; in the first case, the molecular weight is increased and the symmetry diminished, the increase of boiling-point being 82°; in the second case the molecular weight is again increased but the molecule assumes a more symmetrical configuration, hence the comparatively slight increase of 20°.
The thermal effect of the " alcohol " group C. OH may be determined by finding the heat of formation of the alcohol and subtracting the thermal effects of the remaining linkages in the molecule.
It is remarkable that the position of the halogen in the molecule has no effect on the heat of formation; for example, chlorpropylene and allylchloride, and also ethylene dichloride and ethylidene dichloride, have equal heats of formation.
Since a/d is the real specific volume of the molecule, it is therefore a constant; hence (N2-I)/(N2+2)d is also a constant and is independent of all changes of temperature, pressure, and of the state of aggregation.
The nitro group has a very important action mainly on account of the readiness with which it can be introduced into the molecule, but its effect is much less than that of the azo group. The colour produced is generally yellow, which, in accordance with a general rule, is intensified with an increase in the number of groups; compare, for example, mono-, diand tri-nitrobenzene.
The carbonyl group by itself does not produce colour, but when two adjacent groups occur in the molecule, as for example in the a-diketones (such as di-acetyl and benzil), a yellow colour is produced.
According to the modern theory of auxochromic action, the introduction of a group into the molecule is accompanied by some strain, and the alteration in colour produced is connected with the magnitude of the strain.
The method is based on the supposition that the magnetic rotation measures the strain produced in the molecule by an auxochrome, and he arranges the groups in the following order: O.
(2) The chromophore-auxochrome theory (Kauffmann) regards colour as due to the entry of an " auxochrome " into a " chromophoric " molecule.
C. C. Baly regards colour as due to " isorropesis " or an oscillation between the residual affinities of adjacent atoms composing the molecule.
Soc.), regards the property as occasioned by internal vibrations within the molecule conditioned by a symmetrical double tautomerism, light of one wave-length being absorbed by one form, and emitted with a different wave-length by the other.
This theory explains the fluorescence of anthranilic acid (o-aminobenzoic acid), by regarding the aniline residue as the luminophore, and the carboxyl group as the fluorogen, since, apparently, the introduction of the latter into the non-fluorescent aniline molecule involves the production of a fluorescent substance.
n is the mean number of molecules which associate to form one molecule, then by the normal equation we have y (Mnv) 3 =2.121(r -6°); if the calculated constant be K 1, then we have also y(Mv)3=K,(r-6°).
Isomorphism may be defined as the existence of two or more different substances in the same crystal form and structure, polymorphism as the existence of the same substance in two or more crystal modifications, and morphotropy (after P. von Groth) as the change in crystal form due to alterations in the molecule of closely (chemically) related substances.
The measure of the loss of symmetry associated with the introduction of alkyl groups depends upon the relative magnitudes of the substituent group and the rest of the molecule; and the larger the molecule, the less would be the morphotropic effect of any particular substituent.
The nitro group behaves very similarly to the hydroxyl group. The effect of varying the position of the nitro group in the molecule is well marked, and conclusions may be drawn as to the orientation of the groups from a knowledge of the crystal form; a change in the symmetry of the chemical molecule being often attended by a loss in the symmetry of the crystal.
This reflection is suggested by the following articles: Aether; Molecule; Capillary Action; Diffusion; Radiation, Theory Of; and others.
Thus, if the molecule of a substance in solution is represented by AB, Grotthus considered a chain of AB molecules to exist from one electrode to the other.
Under the influence of an applied electric force, he imagined that the B part of the first molecule was liberated at the anode, and that the A part thus isolated united with the B part of the second molecule, which, in its turn, passed on its A to the B of the third molecule.
In this manner, the B part of the last molecule of the chain was seized by the A of the last molecule but one, and the A part of the last molecule liberated at the surface of the cathode.
As we have seen, Grotthus imagined that it was the electric forces which sheared the ions past each other and loosened the chemical bonds holding the opposite parts of each dissolved molecule together.
Clausius extended to electrolysis the chemical ideas which looked on the opposite parts of the molecule as always changing partners independently of any electric force, and regarded the function of the current as merely directive.
Arrhenius pointed out that these exceptions would be brought into line if the ions of electrolytes were imagined to be separate entities each capable of producing its own pressure effects just as would an ordinary dissolved molecule.
(I) In very dilute solutions of simple substances, where only one kind of dissociation is possible and the dissociation of the ions is complete, the number of pressure-producing particles necessary to produce the observed osmotic effects should be equal to the number of ions given by a molecule of the salt as shown by its electrical properties.
The electrical phenomena show that there are two ions to the molecule, and that these ions are electrically charged.
Corresponding with this result we find that the freezing point of dilute solutions indicates that two pressure-producing particles per molecule are present.
In other cases, such as that of litmus, both the ion and the undissociated molecule are coloured, but in different ways.
When the solutions may be taken as effectively dilute, so that the gas laws apply to the osmotic pressure, this relation reduces to E _ nrRT to c1 ey gE c2 where n is the number of ions given by one molecule of the salt, r the transport ratio of the anion, R the gas constant, T the absolute temperature, y the total valency of the anions obtained from one molecule, and c i and c 2 the concentrations of the two solutions.
If ozone is passed into a solution of rubber in chloroform the caoutchouc combines with a molecule of ozone forming a compound of the empirical composition C 5 H 8 O 8.
This result he considered to be due, not to any removal of impurities, but to an actual splitting-up of the yttrium molecule into its constituents, and he ventured to draw the provisional conclusion that the so-called simple bodies are in reality compound molecules, at the same time suggesting that all the elements have been produced by a process of evolution from one primordial stuff or "protyle."
Since the molecule contains an asymmetric carbon atom, the acid exists in three forms, one being an inactive "racemic" mixture, and the other two being optically active forms. The inactive variety is known as paramandelic acid.
Weber therefore supposed each molecule to be acted on by a force tending to preserve it in its original direction, the position actually assumed by the axis being in the direction of the resultant of this hypothetical force and the applied magnetizing force.
Maxwell (Electricity and Magnetism, § 444), recognizing that the theory in this form gave no account of residual magnetization, made the further assumption that if the deflection of the axis of the molecule exceeded a certain angle, the axis would not return to its original position when the deflecting force was removed, but would retain a permanent set.
The fact being established that magnetism is essentially a molecular phenomenon, the next step is to inquire what is the constitution of a magnetic molecule, and why it is that some molecules are ferromagnetic, others paramagnetic, and others again diamagnetic. The best known of the explanations that have been proposed depend upon the magnetic action of an electric current.
Ferromagnetism was explained by Ampere on the hypothesis that the magnetization of the molecule is due to an electric current constantly circulating within it.
The creation of an external magnetic field H will, in accordance with Lenz's law, induce in the molecule an electric current so directed that the magnetization of the equivalent magnet is opposed to the direction of the field.
round the molecule until the field is withdrawn, when it will be stopped by the action of an electro-motive force tending to induce an exactly equal current in the opposite direction.
Since that date it has more than once been suggested that the molecular currents producing magnetism might be due to the revolution of one or more of the charged atoms or " ions " constituting the molecule.
As a consequence of the structure of the molecule, which is an aggregation of atoms, the planes of the orbits around the latter may be oriented in various positions, and the direction of revolution may be right-handed or left-handed with respect to the direction of any applied magnetic field.
If the structure of the molecule is so perfectly symmetrical that, in the absence of any external field, the resultant magnetic moment of the circulating electrons is zero, then the application of a field, by accelerating the right-handed (negative) revolutions, and retarding those which are left-handed, will induce in the substance a resultant magnetization opposite in direction to the field itself; a body composed of such symmetrical molecules is therefore diamagnetic. If however the structure of the molecule is such that the electrons revolving around its atoms do not exactly cancel one another's effects, the molecule constitutes a little magnet, which under the influence of an external field will tend to set itself with its axis parallel to the field.
As the carbon content of the molecule increases, they become less soluble in water, and their smell becomes less marked with the increase in boiling point, the highest members of the series being odourless solids, which can only be distilled without decomposition invacuo.
Substitution takes place usually in the nucleus and only rarely in the side chain, and according to the conditions of the experiment and the nature of the compound acted upon, one or more nitro groups enter the molecule.
The nitro group in the aromatic series is bound very firmly in the molecule and is not readily exchanged for other groups.
The acid salts are obtained by the addition of one molecule of alkali to two molecules of the acid in concentrated alcoholic solution at a low temperature.
The oldest and perhaps most reasonable idea represents guncotton as cellulose trinitrate, but this has been much disputed, and various formulae, some based on cellulose as C, 2 H200 10, others on a still more complex molecule, have been proposed.
Strong or weak solutions of these substances also decompose it, producing some alkali nitrate and nitrite, the cellulose molecule being only partially restored, some quantity undergoing oxidation.
Some glycerin may be re-formed, but with very strong alkaline solutions little of the glycerin molecule escapes destruction, oxalic acid and several other products resulting.
Fraser proved that by substitution of molecules in certain compounds a stimulant could be converted into a sedative action; thus by the addition of the methyl group CH 2 to the molecule of strychnine, thebaine or brucine, the tetanizing action of these drugs is converted into a paralysing action.
In addition trisaccharoses are known of the formula C13H32016; these on hydrolysis yield one molecule of a monosaccharose and one of a disaccharose, or three of a monosaccharose.
- Fischer found that if one molecule of phenylhydrazine acted upon one molecule of an aldose or ketose a hydrazone resulted which in most cases was very soluble in water, but if three molecules of the hydrazine reacted (one of which is reduced to ammonia and aniline) insoluble crystalline substances resulted, termed osazones, which readily characterized the sugar from which it was obtained.
The plane projection of molecular structures which differ stereochemically is discussed under Stereoisomerism; in this place it suffices to say that, since the terminal groups of the hexaldose molecule are different and four asymmetric carbon atoms are present, sixteen hexaldoses are possible; and for the hexahydric alcohols which they yield on reduction, and the tetrahydric dicarboxylic acids which they give on oxidation, only ten forms are possible.
Employing the notation in which the molecule is represented vertically with the aldehyde group at the bottom, and calling a carbon atom+or - according as the hydrogen atom is to the left or right, the possible configurations are shown in the diagram.
Fischer has proposed formulae for the important disaccharoses, and in conjunction with Armstrong devised a method for determining how the molecule was built up, by forming the osone of the sugar and hydrolysing, whereupon the hexosone obtained indicates the aldose part of the molecule.
At Ioo° C. the crystals lose 6 of their molecules of water; the remaining molecule goes off at 250°, a temperature which lies close to that at which the salt begins to decompose.
The next higher members of the series are liquids of low boiling point also readily soluble in water, the solubility and volatility, however, decreasing with the increasing carbon content of the molecule, until the highest members of the series are odourless solids of high boiling point and are insoluble in water.
If the nitrogen atom in the quaternary ammonium salts be in combination with four different groups, then the molecule is asymmetrical, and the salt can be resolved into optically active enantiamorphous isomerides.
Again, anode reactions, such as are observed in the electrolysis of the fatty acids, may be utilized, as, for example, when the radical CH3C02 - deposited at the anode in the electrolysis of acetic acid - is dissociated, two of the groups react to give one molecule of ethane, C 2 H 6, and two of carbon dioxide.
This view, which was specially supported by Gay-Lussac and Leopold Gmelin and accepted by Berzelius, necessitated that all acids were monobasic. The untenability of this theory was proved by Thomas Graham's investigation of the phosphoric acids; for he then showed that the ortho- (ordinary), pyroand metaphosphoric acids contained respectively 3, 2 and I molecules of " basic water " (which were replaceable by metallic oxides) and one molecule of phosphoric oxide, P2 05.
The isomerism which occurs as soon as the molecule contains a few carbon atoms renders any classification based on empirical molecular formulae somewhat ineffective; on the other hand, a scheme based on molecular structure would involve more detail than it is here possible to give.
In the preceding instances the carboxyl group has been synthesized or introduced into a molecule; we have now to consider syntheses from substances already containing carboxyl groups.
potassium and the rest of the molecule.
Phosphorus chlorides give acid chlorides, Rï¿½COï¿½C1, the hydroxyl group being replaced by chlorine, and acid anhydrides, (Rï¿½CO) 2 0, a molecule of water being split off between two carboxyl groups.
The ammonium salts when heated lose one molecule of water and are converted into acid-amides, R.
Beside the ordinary acid and neutral salts, a series of salts called quadroxalates is known, these being salts containing one molecule of acid salt, in combination with one molecule of acid, one of the most common being "salt of sorrel," KHC 2 0 4.
Their experiments, although not conclusive, appear to indicate that the molecule of a metal when in dilute solution often consists of one atom.
In the cases of aluminium dissolved in tin and of mercury or bismuth in lead, it is at least probable that the molecules in solution are Al 2j Hg 2 and Bit respectively, while tin in lead appears to form a molecule of the type Sn4.
The value of the index, n, appears to be different for different types of molecule.
We may therefore reasonably assume that the limiting values of the specific heats at zero pressure do not vary with the temperature, provided that the molecule is stable and there is no dissociation.
If two monatomic molecules, having energy of translation only, equivalent to 3 degrees of freedom, combined to form a diatomic molecule with 5 degrees of freedom, the energy lost would.
If two diatomic molecules, having each 5 degrees of freedom, combine to form a molecule with 6 degrees of freedom, we should have n = 2, or the energy lost would be 2pc per unit mass.
They are continually changing partners, the ratio c/V representing approximately the ratio of the time during which any one molecule is paired to the time during which it is free.
m, Mass of substance or molecule.
In air of considerable density the mean free path of a molecule, between its collisions with other molecules, is exceedingly small, and any such increase of gaseous pressure in front of the black surface would be immediately neutralized by flow of the gas from places of high to places of low pressure.
MOLECULE (from mod.
" Atom " has mainly a chemical import, being defined as the smallest particle of matter which can take part in a chemical reaction; a " molecule " is composed of atoms, generally two or more.
" The opposite school maintained then, as they have always done, 1 It wiII be noted that Clerk Maxwell's " atom " and " atomic theory " have the significance which we now attach to " molecule " and " molecular theory."
For instance, if oxygen and hydrogen combine to form water, we have no experimental evidence that the molecule of oxygen is not in the very same place with the two molecules of hydrogen.
The smallest unit of matter with which physical phenomena are concerned is the molecule.
When chemical phenomena occur the molecule may be divided into atoms, and these atoms, in the presence of electrical phenomena, may themselves be further divided into electrons or corpuscles.
At a certain temperature a stage will be reached in which it is a frequent occurrence for a molecule to wander so far from its position of equilibrium, that it does not return but falls into a new position of equilibrium and oscillates about this.
A molecule escaping from its original position in a body will usually fall into a new position in which it will be held in equilibrium by the forces from a new set of neighbouring molecules.
But if the wandering molecule was originally close to the surface of the body, and if it also happens to start off in the right direction, it may escape from the body altogether and describe a free path in space until it is checked by meeting a second wandering molecule or other obstacle.
When a liquid undergoing evaporation is contained in a closed vessel, a molecule which has left the liquid will, after a certain 1 Other processes also help in the conduction of heat, especially in substances which are conductors of electricity.
(If the molecules of air at normal temperature and pressure were arranged in cubical order, the edge of each cube would be about 2.9 X I o - ' cms.; the average diameter of a molecule in air is 2.8X Io - 8 cms.) Further and very important evidence as to the nature of the gaseous state of matter is provided by the experiments of Joule and Kelvin.
A number of molecules moving in obedience to dynamical laws will pass through a series of configurations which can be theoretically determined as soon as the structure of each molecule and the initial position and velocity of every part of it are known.
(5) If c is the resultant velocity of a molecule, so that c 2 =u2+v2+w2, it is readily found from formula (4) that the number of molecules of the first kind of which the resultant velocity lies between c and c+dc is 4lrs1,l (h 3 rn 3 17r 3)e hmc2 c 2 dc. (6) These formulae express the " law of distribution of velocities " in the normal state: the law is often called Maxwell's Law of Distribution.
Each impinging molecule exerts an impulsive pressure equal to mu on the boundary before the component of velocity of its centre of gravity normal to the boundary is reduced to zero.
If p is the density corresponding to pressure p, we find that,}, formula (Ii) assumes the form P = 3PC2, where C is a velocity such that the gas would have its actual translational energy if each molecule moved with the same velocity C. By substituting experimentally determined pairs of values of p and p we can calculate C for different gases, and so obtain a knowledge of the magnitudes of the molecular velocities.
35 X I 016 it is readily calculated that a molecule, or aggregation of molecules, of mass Io - 12 grammes, ought to have a mean velocity of about 2 millimetres a second at O.
The value of n is the number of terms in the energy of the molecule beyond that due to translation.
No molecule could possibly be imagined for which n had a negative value or the value n =1.
SAFRANINE, in chemistry, the azonium compounds of symmetrical diamino-phenazine and containing the ring system annexed: / N / or X N .% CI R C1 R They are obtained by the joint oxidation' of one molecule of a paradiamine with two molecules of a primary amine; by the condensation of para-aminoazo compounds with primary amines (0.
Pyrophosphoric acid, 'H' 4 P 2 0 7, is a tetrabasic acid which may be regarded as derived by eliminating a molecule of water between two molecules of ordinary phosphoric acid; its constitution may therefore be written (HO) 2 0P O PO(OH) 2.
Metaphosphoric acid, HP0 3, is a monobasic acid which may be regarded as derived from orthophosphoric acid by the abstraction of one molecule of water, thus H 3 PO 4 - H 2 O = HP0 3; its constitution is therefore (HO)P0 2.
Of the acid orthophosphates, the mono-calcium salt, CaH4(P04)2, may be obtained as crystalline scales, containing one molecule of water, by evaporating a solution of the normal salt in hydrochloric or nitric acid.
Soc., 1889, 55, p. 163) determined the vapour density of hydrofluoric acid at different temperatures, and showed that there is no approach to a definite value below about 88° C. where it reaches the value 10.29 corresponding to the molecular formula HF; at temperatures below 88° C. the value increases rapidly, showing that the molecule is more complex in its structure.
A characteristic property of the alkaline fluorides is their power of combining with a molecule of hydrofluoric acid and with the fluorides of the more electro-negative elements to form double fluorides, a behaviour not shown by other metallic halides.
The modification of the spectrum of a radiating gas by a magnetic field, such as would result from the hypothesis that the radiators are the system of revolving or oscillating electrons in the molecule, was detected by P. Zeeman in 1896, and worked up, in conjunction with H.
See also MOLECULE, ELECTRICITY, LIGHT and RADIATION.
Chemie, 1867, 3, p. 39), ascribes to the molecule a peroxide configuration which accounts for its oxidizing powers but not for the fact that each oxygen atom is capable of replacement by one atom of chlorine.
Thus, if one molecule is disturbed from its mean position, it communicates the disturbance to its neighbours, and so a wave is propagated.
8.89 8.84 8.73 6-08 5.75 5.67 This shows that the iodine molecule becomes less complex in structure at higher temperatures.
It is obtained by hydrolysing cocaine with acids or alkalis, and crystallizes with one molecule of water, the crystals melting at 198° to 199° C. It is laevo-rotatory, and on warming with alkalis gives iso-ecgonine, which is dextro-rotatory.
Chromium salts readily combine with ammonia to form complex salts in which the ammonia molecule is in direct combination with the chromium atom.
In many of these salts one finds that the elements of water are frequently found in combination with the metal, and further, that the ammonia molecule may be replaced by such other molecular groups as - N02, &c. Of the types studied the following may be mentioned: the diammine chromium thiocyanates, M[Cr(NH3)2 (SCN)4], the chloraquotetrammine chromic salts, R 1 2 [Cr(NH 3) 4 H 2 0 C1], the aquopentammine or roseo-chromium salts,R 1 3 [Cr(NH 3) 6.
When the molecule is losing energy the intensity of each kind of radiation depends principally on the rapidity with which it can be renewed by molecular impacts.
Radiation is a molecular process, and we can speak of the radiation of a molecule but not of its temperature.
The problem, which, in the opinion of the present writer, is the one of interest and has more or less definitely been in the minds of those who have discussed the subject, is whether the type of wave sent out by a molecule only depends on the internal energy of that molecule, or on other considerations such as the mode of excitement.
The energy of radiation resides in the medium and not in the molecule.
Considering the great variety of spectra, which one and the same body may possess, the idea lies near that free electrons may temporarily attach themselves to a molecule or detach 'themselves from it, thereby altering the constitution of the vibrating system.
Thus if a molecule were set into vibration at a specified time and oscillated according to the above equation during a finite period, it would not send out homogeneous vibrations.
A limit to homogeneity of radiation is ultimately set by the so-called Doppler effect, which is the change of wave-length due to the translatory motion of the vibrating molecule from or towards the observer.
If N be the frequency of a homogeneous vibration sent out by a molecule at rest, the apparent frequency will be N (1 v/ V), where V is the velocity of light and v is the velocity of the line of sight, taken as positive if the distance from the observer increases.
Such spectra seem to be characteristic of complex molecular structure, as they appear when compounds are raised to incandescence without decomposition, or when we examine the absorption spectra of vapours such as iodine and bromine and other cases where we know that the molecule consists of more than one atom.
Each molecule need not radiate with increased energy, but the more brilliant emission of light may be due to the greater number of particles forming similar vibrating systems.
Compounds generally show spectra of resolvable bands, and if an elementary body shows a spectrum of the same type we are probably justified in assuming it to be due to a complex molecule.
But that it may be given by the ordinary diatomic molecule is exemplified by oxygen, which gives in thick layers by absorption one of the typical sets of bands which were used by Deslandres and others to investigate the laws of distribution of frequencies.
To explain this great variability of spectroscopic effects we may either adopt the view that molecular aggregates of semi-stable nature may be found in vacuum tubes, or that a molecule may gain or lose one or more additional electrons and thus form new vibrating systems. It seemed that an important guide to clear our notions in this direction could be obtained through the discovery of J.
No conclusion can therefore be drawn, as Stark' has more recently pointed out, respecting the charge of the molecule which emits the observed spectrum.
Applying the reasoning to the case of a homogeneous radiation traversing an absorbing medium, we realize that the mutual disturbances of the molecules by collision or otherwise must bring in the free period of the molecule whatever the incident radiation may be.
It will be advantageous if the spectra of ammonia, benzene, aniline and dimethyl aniline be compared, when the re-' markable coincidences will at once become apparent, as also the different weighting of the molecule.
In order to explain the electrical properties of a solution, for instance of potassium chloride, we are driven to believe that each molecule of the salt is dissociated into two parts, potassium and chlorine, each associated with an electric charge equal in amount but opposite in sign.
The greater the number of water molecules attached to one sugar molecule, the less the residual volume, and the greater the theoretical pressure.
Boltzmann offered a demonstration of the law of osmotic pressure in dilute solutions, based on the idea that the mean energy of translation of a molecule should be the same in the liquid as in the gaseous state.
If each molecule of the solute combines with a certain number of molecules of the solvent in such a way as to render them inactive for evaporation, we get a lowering of vapour pressure.
Each molecular complex, formed by solution and solvent, is treated as a single molecule.
If there are n molecules of solute to N of solvent originally, and each molecule of solute combines with a molecule of solvent, we get for the ratio of vapour pressures p/p'=(N - an)/(N - an+n), while the relative lowering of vapour pressure is (p - p')/p=n/(N - an).
The same value had previously been found for mercury vapour by Kundt and Warburg, and had been regarded as confirmatory of the monatomic character attributed on chemical grounds to the mercury molecule.
On oxidation, the molecule is split at the carbonyl group and a mixture of acids is obtained.
In the latter reaction it is assumed that the isodiazohydroxide first formed is immediately attacked by a second molecule of the amine.
Traube, Ber., 1882, 15, p. 659); in the oxidation of zinc, lead and copper in presence of water, and in the electrolysis of sulphuric acid of such strength that it contains two molecules of water to one molecule of sulphuric acid (M.
the molecules, are identical, and so the molecule of both butylene and isobutylene is indicated by the same chemical symbol C4118, expressing that each molecule contains, in both cases, four atoms of carbon (C) and eight of hydrogen (H).
This explains a good deal of the possible instability; and, from a practical point of view, it coincides with the fact that such a large amount of energy can be stored in our most intense explosives such as dynamite, the explanation being that hydrogen is attached to carbon distant from oxygen in the same molecule, and that only the characteristic resistance of the carbon linkage prevents the hydrogen from burning, which is the main occurrence in the explosion of dynamite.
the conception as to the order in which the atoms composing a molecule are linked together.
This conception has rendered possible a clear idea of the linking or internal structure of the molecule, for example, in the most simple case, methane, CH 4, is expressed by H H-C-H H It is by this conception that possible and impossible compounds are at once fixed.
In this equation a relates to molecular attraction; and it is not improbable that in isomeric molecules, containing in sum the same amount of the same atoms, those mutual attractions are approximately the same, whereas the chief difference lies in the value of b, that is, the volume occupied by the molecule itself.
For what reason this volume may differ from case to case lies close at hand; in connexion with the notion of negative and positive atoms, like chlorine and hydrogen, experience tends to show that the former, as well as the latter, have a mutual repulsive power, but the former acts on the latter in the opposite sense; the necessary consequence is that, when those negative and positive groups are distributed in the molecule, its volume will be smaller than if the negative elements are heaped together.
Other physical properties might be considered; as a general rule they depend upon the distribution of negative and positive elements in the molecule.
The investigation also showed that the nature of the acid used affected the result, for in an homologous series of acids it was found that as the molecule of the acid became more complex, the rate of esterification became less.
The high conductivity of metals is then explained by the small mass and high velocity of diffusion of these electric atoms. Assuming the kinetic energy of an electric atom at any temperature to be equal to that of a gaseous molecule, its velocity, on Sir J.
Thomson's estimate of the mass, must be upwards of forty times that of the hydrogen molecule.
This, at first sight, paradoxical result is explained by the fact that the mean free path of each molecule increases in the same proportion as the density is diminished, so that as the number of molecules crossing each square centimetre decreases, the distance to which each carries its momentum increases, and the total transfer of momentum is unaffected by variation of density.
Its vapour density at 1728° corresponds to the molecule TI 2.
Schonbein (loc. cit.) assumed that the ordinary oxygen molecule is decomposed into two parts which carry electrical charges of opposite kinds, the one with the positive charge being called "antozone" and the other carrying the negative charge being called "ozone," one variety being preferentially used up by the oxidizing compound or element and the other for the secondary reaction.
Traube (loc. cit.), on the other hand, concludes that the oxygen molecule enters into action as a whole and that on the oxidation of metals, hydrogen peroxide and the oxide of the metal are the primary products of the reaction.
Only so much lime is used that an acid manganite is formed corresponding to one molecule of calcium oxide to two of manganous oxide.
They may be regarded as the anhydrides of the alcohols, being formed by elimination of one molecule of water from two molecules of the alcohols; those in which the two hydrocarbon radicals are similar are known as simple ethers, and those in which they are dissimilar as mixed ethers.
It separates from benzene and thiophene with one molecule of the "solvent of crystallization."
Thus The Direct Experimental Evidence Is Somewhat Meagre And Conflicting, But The Question Of The Relation Of The Specific Heats Of Gases Is One Of Great Interest In Connexion With The Kinetic Theory And The Constitution Of The Molecule.
For Diatomic Or Compound Gases Clerk Maxwell Supposed That The Molecule Would Also Possess Energy Of Rotation, And Endeavoured To Prove That In This Case The Energy Would Be Equally Divided Between The Six Degrees Of Freedom, Three Of Translation And Three Of Rotation, If The Molecule Were Regarded As A Rigid Body Incapable Of Vibration Energy.
Boltzmann Suggested That A Diatomic Molecule Regarded As A Rigid Dumb Bell Or Figure Of Rotation, Might Have Only Five Effective Degrees Of Freedom, Since The Energy Of Rotation About The Axis Of Symmetry Could Not Be Altered By Collisions Between The Molecules.
For A Rigid Molecule On This Theory The Smallest Value Possible Would Be 4/3.
Since Much Smaller Values Are Found For More Complex Molecules, We May Suppose That, In These Cases, The Energy Of Rotation Of A Polyatomic Molecule May Be Greater Than Its Energy Of Translation, Or Else That Heat Is Expended In Splitting Up Molecular Aggregates, And Increasing Energy Of Vibration.
A Hypothesis Doubtfully Attributed To Maxwell Is That Each Additional Atom In The Molecule Is Equivalent To Two Extra Degrees Of Freedom.
From An M Atomic Molecule We Should Then Have S/S= 2/(2M I).
This Gives A Series Of Ratios 5/3, 7/5, 9/7, Ii/9, &C., For I, 2, 3, 4, &C., Atoms In The Molecule, Values Which Fall Within The Limits Of Experimental Error In Many Cases.
Two hydrated forms have been described, one containing three molecules of water and the other half a molecule.
It is assumed that each molecule of solute combines with a molecules of solvent according to the ordinary law of chemical combination, and that the number a, representing the degree of hydration, remains constant within wide limits of temperature and concentration.
The explanation of this relation is that each of the n compound molecules counts as a single molecule, and that, if all the molecules were solvent molecules, the vapour-pressure would be p', that of the pure solvent.
The highest pressures recorded for cane-sugar are nearly three times as great as those given by van't Hoff's formula for the gas-pressure, but agree very well with the vapour-pressure theory, as modified by Callendar, provided that we substitute for V in Arrhenius's formula the actual specific volume of the solvent in the solution, and if we also assume that each molecule of sugar in solution combines with 5 molecules of water, as required by the observations on the depression of the freezing-point and the rise of the boiling-point.
1900) adopted the mean value n=3.5, and also assumed the specific heat at constant volume s =3.5 R (which gives So=4.5 R) on the basis of an hypothesis, doubtfully attributed to Maxwell, that the number of degrees of freedom of a molecule with m atoms is 2m +I.
1 Clerk Maxwell had already used in 1873 the phrase, " a molecule of electricity."
pp. 268 et seq.); and conversely on boiling with dilute acids or alkalis it takes up a molecule of water and yields two molecules of gallic acid, C 7 H 6 0 5.
If we suppose that the number of molecules within the range of the attraction of a given molecule is very large, the part of the pressure arising from attraction will be proportional to the square of the number of molecules in unit of volume, that is, to the square of the density.
The energy liberated during the oxidation of the nitrogen is regarded as splitting the carbon dioxide molecule, - in green plants it is the energy of the solar rays which does this.
In the first place, the extremely small size and isolation of the vegetative cells place the protoplasmic contents in peculiarly favourable circumstances for action, and we may safely conclude that, weight for weight and molecule for molecule, the protoplasm of bacteria is brought into contact with the environment at far more points and over a far larger surface than is that of higher organisms, whether - as in plants - it is distributed in thin layers round the sap-vacuoles, or - as in animals - is bathed in fluids brought by special mechanisms to irrigate it.
is usually stated that the carbon dioxide molecule is here.
In other cases such changes cannot be detected, and the only evidence of their occurrence may be the associated symptoms. The very important work of Ehrlich on diphtheria toxin shows that in the molecule of toxin there are at least two chief atom groups - one, the " haptophorous," by which the toxin molecule is attached to the cell protoplasm; and the other the " toxophorous," which has a ferment-like action on the living molecule, producing a disturbance which results in the toxic symptoms. On this theory, susceptibility to a toxin will imply both a chemical affinity of certain tissues for the toxin molecule and also sensitiveness to its actions, and, furthermore, non-susceptibility may result from the absence of either of these two properties.
It may produce a disintegration of the toxin molecule, or it may combine with it to produce a body whose combining affinities are satisfied.
His view as to the dual composition of the toxin molecule has already been mentioned, and it is evident that if the haptophorous or combining group has its affinity satisfied by union with antitoxin, the toxin will no longer combine with living cells, and will thus be rendered harmless.
Still another view, advocated by Bordet, is that the union of toxin and antitoxin is rather of physical than of strictly chemical nature, and represents an interaction of colloidal substances, a sort of molecular deposition by which the smaller toxin molecule becomes entangled in the larger molecule of antitoxin.
Living protoplasm, or in other words a biogen molecule, is regarded as consisting of a central atom group (Leistungskern), related to which are numerous secondary atom groups or sidechains, with unsatisfied chemical affinities.
The' side-chains constitute the means by which other molecules are added to the living molecule, e.g.
Natural immunity against toxins must be taken into account, and, if Ehrlich's view with regard to toxic action be correct, this may depend upon either the absence of chemical affinity of the living molecules of the tissues for the toxic molecule, or upon insensitiveness to the action of the toxophorous group. It has been shown with regard to the former, for example, that the nervous system of the fowl, which possesses immunity against tetanus toxin, has little combining affinity for it.
Soc. Morphine, or morphia, crystallizes in prisms with one molecule of water; it is soluble in woo parts of cold water and in 160 of boiling water, and may be crystallized from alcohol; it is almost insoluble in ether and chloroform.
Codeine, or codeia, crystallizes in orthorhombic prisms with one molecule of water: it is readily soluble in alcohol, ether and chloroform.
Its vapour density has been determined at 2000°, and corresponds to a monatomic molecule.
Silver fluoride, AgF, is obtained as quadratic octahedra, with one molecule of water, by dissolving the oxide or carbonate in hydrofluoric acid.
Two lactic acids are known, differing from each other in the position occupied by the hydroxyl group in the molecule; they are known respectively as a-hydroxypropionic acid (fermentation or inactive lactic acid), CH 3 CH(OH) CO 2 H, ands-hydroxypropionic acid (hydracrylic acid), (q.v.), CH2(OH) CH 2 CO 2 H.
The band spectrum, which corresponds to the compound or at least to the molecule of titanium, certainly belongs to a lower temperature than the line spectrum of the same metal.
Canine is a secondary base, forming a nitroso derivative with nitrous acid, a urethane with chlorcarbonic ester and a tertiary base (methyl conine) with methyl iodide; reactions which point to the presence of the = NH group in the molecule.
Numerous substitution products of quinoline are known, and the positions in the molecule are generally designated in accordance with the scheme shown in the inset formula: the letters o, m, p, a, standing for ortho-, meta-, Para-, and ana-.
Thus 0 2.4 indicates the presence of two double bonds in the molecule situated immediately after the carbon atoms 2 and 4; for example II.
Unsaturated hydrocarbons of the series may be prepared from the corresponding alcohols by the elimination of a molecule of water, using either the xanthogenic ester method of L.
- Two types of ketones are to be noted in this group, namely the a/3 and, fay ketones, depending upon the position of the double linkage in the molecule, thus: H2C / CH2: CH CO HC?
The term "perfect gas" is applied to an imaginary substance in which there is no frictional retardation of molecular motion; or, in other words, the time during which any molecule is influenced by other molecules is infinitesimally small compared with the time during which it traverses its mean free path.
This subject, which is discussed in the article Molecule, has for its purpose (I) the derivation of a physical structure of a gas which will agree with the experimental observations of the diverse physical properties, and (2) a correlation of the physical properties and chemical composition.
Vapour density determinations at 448° indicate a partial dissociation of the double molecule Fe2Cl6I on stronger heating it splits into ferrous chloride and chlorine.
The coloration is due to the production of unstable compounds of the ferrous salt and nitric oxide, and it seems that in neutral solutions the compound is made up of one molecule of salt to one of gas; the reaction, however, is reversible, the composition varying with temperature, concentration and nature of the salt.
In the following year he published at Vienna his famous work, Theoria philosophiae naturalis redacta ad unicam legem virium in natura existentium, containing his atomic theory (see MOLECULE).
If, however, a second molecule of a zinc alkyl be allowed to react, a compound is formed which gives a tertiary alcohol when decomposed with water.
The vapour density is 10.6 (air =1) at 564° C., corresponding to a tetratomic molecule As; at a white heat the vapour density shows a considerable lowering in value, due to the dissociation of the complex molecule.
As it is we shall find a continuous molecule manifesting attractive and repulsive forces; attraction corresponding to the tendency of the self-preservations to become perfect, repulsion to the frustration of this.
Heated with an excess of lime it gives benzene; calcium benzoate results when calcium phthalate is heated with one molecule of lime to 330°-350°.
A brief paper entitled "Speculative Ideas on the Constitution of Matter" (1863) possesses special interest in connexion with work done since his death, because in it he expressed the view that the various kinds of matter now recognized as different elementary substances may possess one and the same ultimate or atomic molecule in different conditions of movement.
The word usage examples above have been gathered from various sources to reflect current and historial usage. They do not represent the opinions of YourDictionary.com.