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Question 71 of 84

Q.How will you determine the ionic character in covalent bond using electronegativity values? OR Give the IUPAC names of the following compounds.

(i) CH3-CH(CH3)-CH(Br)-CH3
(ii) CH3-O-CH3
(iii) CH3-CH2-CH(OH)-CHO
(iv) CH2=CH-CH=CH2
(v) CH3-C#C-CH(Cl)-CH3 (# = triple bond)
Tamil Nadu DgeTamil Nadu HSC First Year (DGE) Board 2022Subjective· 5mImportance★★★★★
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A covalent bond gains ionic character in proportion to the electronegativity difference between the two bonded atoms; a larger electronegativity difference pulls the shared electron pair more towards the more electronegative atom, and this can be quantified using an empirical formula based on that difference.

(This question offered an OR alternative on IUPAC naming of five compounds; the primary question on ionic character is answered below.)

In a purely covalent bond between two identical atoms (e.g., H-H, Cl-Cl), the electronegativity difference (ΔEN) is zero and the electron pair is shared exactly equally — 0% ionic character.

When the two bonded atoms have different electronegativities, the shared electron pair is pulled more towards the more electronegative atom, creating a partial negative charge (delta-) on it and a partial positive charge (delta+) on the other atom — the bond acquires partial ionic character, and the larger the ΔEN, the greater this ionic character.

An empirical relation (the Hannay-Smyth equation) connects the electronegativity difference directly to the percentage ionic character of the bond:

% ionic character = 16(ΔEN) + 3.5(ΔEN)^2

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