You need to look for a hydrogen atom covalently bonded to a highly electronegative atom, usually nitrogen, oxygen or fluorine.
In other words, as you go down the Group, the elements become less electronegative.
All of these particular cases contain a very electronegative element with an active lone pair of electrons - either oxygen or nitrogen.
Moreover, a covalent bond between two highly electronegative elements will clearly be strong.
Instances had already been recorded of cases where a halogen element replaced hydrogen with the production of a closely allied substance: Gay Lussac had prepared cyanogen chloride from hydrocyanic acid; Faraday, hexachlorethane from ethylene dichloride, &c. Here the electronegative halogens exercised a function similar to electro-positive hydrogen.
electronegative oxygen atom is considered to gain both pairs of the bonding electrons with hydrogen.
electronegative than hydrogen.
electronegative than carbon?
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