Give the electron configuration of (a) Pm (b) Lu³⁺ (c) Th (d) Fm³⁺

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

(a) Based on the periodic table, Pm has the atomic number of 61, therefore it has 61 electrons with electron configuration:

1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶6s²4f⁵

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

(b) Based on the periodic table, Lu has the atomic number of 71, therefore it has 71 electrons.

1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶6s²4f¹⁴5d¹

When it gains a charge of 3⁺, it loses 3 electrons, and will have only 68 electrons with electron configuration:

1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶6s²4f¹²

(c) Based on the periodic table, Th has the atomic number of 90, therefore it has 90 electrons with electron configuration:

1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶6s²4f¹⁴5d¹⁰6p⁶7s²5f²

(d) Based on the periodic table, Fe has the atomic number of 100, therefore it has 100 electrons.

1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶6s²4f¹⁴5d¹⁰6p⁶7s²5f¹²

When it gains a charge of 3⁺, it loses 3 electrons, and will have only 88 electrons with electron configuration:

1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶6s²4f¹⁴5d¹⁰6p⁶7s²5f⁹