Question

Write the condensed electron configurations for the following atoms, using the appropriate noble-gas core abbreviations: (a) \(\mathrm{Cs}\), (b) \(\mathrm{Ni}\), (c) Se, (d) Cd, (e) U, (f) \(\mathrm{Pb}\).

Short answer

(a) Cs: \([Xe] 6s^1\) (b) Ni: \([Ar] 4s^2 3d^8\) (c) Se: \([Ar] 4s^2 3d^{10} 4p^4\) (d) Cd: \([Kr] 5s^2 4d^{10} 5p^6 6s^2 4f^{14} 5d^{10}\) (e) U: \([Rn] 7s^2 6d^1 5f^3\) (f) Pb: \([Xe] 6s^2 4f^{14} 5d^{10} 6p^2\)

Step-by-step solution

Find the atomic number of each element.

Look up each element in the periodic table to find the atomic number, which represents the number of electrons in the neutral atom. (a) Cs: atomic number 55 (b) Ni: atomic number 28 (c) Se: atomic number 34 (d) Cd: atomic number 48 (e) U: atomic number 92 (f) Pb: atomic number 82

Full electron configurations.

Write the full electron configuration for each element, using their atomic numbers to determine the order in which the orbitals are filled. This order can be found using the rules for electron configurations (Aufbau principle, Hund's rule, and Pauli exclusion principle). (a) \(\mathrm{Cs}\): 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s¹ (b) \(\mathrm{Ni}\): 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁸ (c) Se: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁴ (d) Cd: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ (e) U: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f³ 6d¹ (f) Pb: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p²

Determine the noble gas core.

For each element, find the preceding noble gas in the periodic table so we can use its electron configuration as our starting point. (a) \(\mathrm{Cs}\): Previous noble gas = Xe (54) (b) \(\mathrm{Ni}\): Previous noble gas = Ar (18) (c) Se: Previous noble gas = Ar (18) (d) Cd: Previous noble gas = Kr (36) (e) U: Previous noble gas = Rn (86) (f) Pb: Previous noble gas = Xe (54)

Condensed configurations using noble gas core abbreviations.

Use the previous noble gas's electron configuration as a starting point, and add the remaining electron configuration for the given element. (a) \(\mathrm{Cs}\): [Xe] 6s¹ (b) \(\mathrm{Ni}\): [Ar] 4s² 3d⁸ (c) Se: [Ar] 4s² 3d¹⁰ 4p⁴ (d) Cd: [Kr] 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ (e) U: [Rn] 7s² 6d¹ 5f³ (f) Pb: [Xe] 6s² 4f¹⁴ 5d¹⁰ 6p²