Number of Unpaired Electrons in Groups?

How many unpaired electrons are present in the ground state of an atom from each of the following groups? Enter the numbers in order, from (a) to (d) in the answer boxes. All 4 numbers must be correct.

A) 5A(15)

B) 4A(14)

C) 7A(17)

D) 8A(18)

1 Answer

  • OK, working through the main groups left to right the outer shell structures will be

    Group I A s1 = one unpaired electron

    Group 2A s2 = 2 paired electrons

    Group 3A s2p1 = 2 paired + 1 unpaired

    Group 4A s2p2 = 2 paired + 2 unpaired

    Group 5A s2p3 = 2 paired + 3 unpaired

    Group 6A s2p4 = 4 paired + 2 unpaired

    Group 7A s2p5 = 6 paired + 1 unpaired

    Group 8A s2p6 = 8 paired

    So

    5A has 3 unpaired electrons

    4A has 2 unpaired electrons

    7A has 1 unpaired electron

    8A has no unpaired electrons

    Hope this is clear. Electrons fill the three p orbitals singly before any pairing takes place which explains the outer shell structure for groups 4A, 5A and 6A

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