Give the electron configuration of (a) La; (b) Ce³⁺ (c) Es; (d) U⁴⁺.

The electron configuration is the distribution of electrons of an atom or molecule (or other physical structure) in atomic or molecular orbitals.

(a) Based on the periodic table, La has the atomic number of 57, therefore it has 57 electrons with electron configuration:

1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶6s²4f⁰5d¹

Instead of being in the 4f orbital, the lone electron went to the d-orbital.

(b) Based on the periodic table, Ce has the atomic number of 58, therefore it has 58 electrons.

1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶6s²4f¹5d¹

When it gains a charge of 3⁺, it loses 3 electrons, and will have only 55 electrons with electron configuration:

1s²2d²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶6s¹

(c) Based on the periodic table, Es has the atomic number of 99, therefore it has 99 electrons with electron configuration:

1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶6s²4f⁴5d¹⁰6p⁶7s²5f¹¹

(d) Based on the periodic table, U has the atomic number of 92, therefore it has 92 electrons.1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶6s²4f¹⁴5d¹⁰6p⁶7s²5f⁴

When it gains a charge of 4⁺, it loses 4 electrons, and will have only 88 electrons with electron configuration:

1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶6s²4f¹⁴5d¹⁰6p⁶7s²