Question

Thallium was used as a poison in the Agatha Christie mystery story "The Pale Horse." Thallium has two possible cationic forms, +1 and +3. The +1 compounds are the more stable. Write the electron structure of the +1 cation of thallium.

a) Tl⁺: 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁶4d¹⁰5s²5p⁶6s²
b) Tl⁺: 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁶4d¹⁰5s²5p⁶
c) Tl⁺: 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁶4d¹⁰5s²5p⁶6s²6p¹
d) Tl⁺: 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁶4d¹⁰5s²

Answer 1

The electron structure of the +1 cation of thallium (Tl+) is [Xe]4f14 5d10 6s2, after it loses one electron from the outermost p orbital. Hence, option b) is the correct notation for Tl+: 1s22s22p63s23p63d104s24p64d104f145s25p66s2.

Step-by-step explanation:

The electron structure of the +1 cation of thallium (Tl+) is obtained by removing one electron from the neutral thallium atom. The neutral thallium atom has the electron configuration [Xe]4f145d106s26p1, where [Xe] represents the filled electron shells of the noble gas xenon.

When thallium forms a +1 cation by losing one electron, it loses the electron from the outermost p orbital, thus the electron configuration of Tl+ would be [Xe]4f145d106s2.

This means the correct electron structure for the Tl+ cation is: Tl+: 1s22s22p63s23p63d104s24p64d104f145s25p66s2 which matches option b). This composition reflects the inert pair effect, where s electrons are not lost as easily in heavier elements.