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Home , Electron configuration

The ns, np, (n-1)d and (n-2)f orbitals are filled in the nth 7.12 Configurations of • Electron configurations can be deduced from the positions of elements in the – shell principal numbers equal period numbers (F ® 2nd period, n=2) – all elements in a period have the same noble-gas core configurations ([He], [Ne], [Ar], …) – all elements in a have analogous valence shell electron configurations (F ® [He]2s22p5; Cl ® [Ne]3s23p5; all halogens ® ns2np5) • The filling order of the orbitals can be obtained from the periodic table Fig. 7.31

• The ns orbitals are filled before the (n-2)f and • Exceptions to the building-up principle (n-1)d orbitals, but are written after them – half-filled d and f subshells have exceptional stability Sc ® core [Ar] ® (K, Ca) 4s2 ® (Sc) 3d1 Cr ® [Ar]3d54s1 instead of [Ar]3d44s2 2 1 1 2 Þ[Ar]4s 3d ® [Ar]3d 4s – completely filled d and f subshells have exceptional stability Example: Write the Cu ® [Ar]3d104s1 instead of [Ar]3d94s2 of , Os. Example: Write the electron configuration Os is in the 6th period ® valence shell n=6 of , Au. Previous noble gas is Xe ® noble-gas core is [Xe] valence shell n=6 noble-gas core [Xe] After Xe ® 2 ns, 14 (n-2)f, and 6 (n-1)d elements After Xe ® 2 6s, 14 4f, and 9 5d elements Þ [Xe]4f145d66s2 Þ [Xe]4f145d96s2 ® [Xe]4f145d106s1

• Anions 7.13 Electron Configurations of – are added until a noble-gas configuration is reached • Cations Example: Write the electron configurations – for p- and s-elements electrons are lost first from of the nitride and oxide ions. the np subshell followed by the ns subshell N ® [He]2s22p3 N3- ® [He]2s22p6 ® [Ne] – for d-elements electrons are lost first from the ns 2 4 2- 2 6 subshell followed by the (n-1)d subshell O ® [He]2s 2p O ® [He]2s 2p ® [Ne] Example: Write the electron configurations of Pb2+ and Pb4+. Pb ® [Xe]4f145d106s26p2 Pb2+ ® [Xe]4f145d106s2 Pb4+ ® [Xe]4f145d10

1 7.14 Electronic Structure and the • The number of valence electrons equals the Periodic Table group # (group # - 10 for p-elements) • The table is divided into s, p, d, and f blocks Example: Write the named by the last occupied subshell being filled configurations of groups 7 and 15. • Valence electrons – electrons in the highest Group 7 ® 7 valence electrons, d-elements occupied principal shell and in partially filled 2 s-electrons and 5 d-electrons subshells of lower principal shells Þ (n-1)d5ns2 • Main groups – s and p elements – group 1 ns1, group 2 ns2, group 13 ns2np1, ..., Group 15 ® 15-10=5 valence electrons, p-elements 2 6 group 18 ns np 2 s-electrons and 3 p-electrons • Secondary groups – d elements Þ ns2np3 – group 3 (n-1)d1ns2, …, group 12 (n-1)d10ns2

• Atomic radii increase down a group and The Periodicity of Atomic Properties decrease from left to right across a period 7.15 Atomic Radius • Half of the distance between the centers of two neighboring atoms – metals - in the phase – - in ()

Fig. 7.34

• Down a group – the principal increases Þ orbitals and electron clouds become larger • Across a period – the nuclear charge increases and the new electrons enter the same principal shell (do not shield each other effectively) Þ the effective nuclear charge increases Þ draws the electrons closer to the nucleus Example: Compare the sizes of Ge, Sn and Se. Sn is below Ge Þ Sn>Ge Ge is to the left of Se Þ Ge>Se

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