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Which of the following element pairs will form an ionic bond? Pair P Elements of Group 1 & Group 2 Q Elements of Group 14 & Group 16 R Elements of Group 2 & Group 17 S Elements of Group 15 & Group 18
Topic: Chemical bonding and electron structures
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Answer
(c) R — elements of Group 2 and Group 17.
An ionic bond needs one element that loses electrons easily and one that gains them easily — a metal on the left of the table with a non-metal on the right. Test each pair. P (Group 1 and Group 2) is two metals: both want to lose electrons, so neither will accept any and they form a metallic, not ionic, bond. Q (Group 14 and Group 16) is two non-metals, which share electrons and bond covalently. S (Group 15 and Group 18) fails for a different reason: Group 18 is the noble gases, already at a stable octet, so they do not bond at all. R is the only pair that pits a metal against a non-metal: a Group 2 atom loses its two electrons to become M2+, two Group 17 atoms take one each to become X-, and the transfer makes an ionic bond, giving MX2 — calcium chloride, CaCl2, is the everyday example.
R — elements of Group 2 and Group 17.