Answer the following questions about the element selenium, Se (atomic number 34). b) Write the complete electron configuration for a selenium atom in the ground state. Indicate the number of unpaired electrons in the ground-state atom, and explain your reasoning. c) In terms of atomic structure, explain why the first ionization energy of selenium is i) less than that of bromine (atomic number 35), and ii) greater than that of tellurium (atomic 52).

Answers and Explanation:

b) Complete electron configuration of Se:

1 s² 2 s²p⁶ 3 s²p⁶ 4 s²p⁴

Se has 4 energy levels, with an incomplete 4th level (they are necessary 2 electrons to complete p orbital in the 4th level).

c) The first ionization energy of Se

i) is less that of bromine (Br) because the first ionization energy increases from left to right in a period in the Periodic Table. Se and Br are in the same period, and Se is located to the left of Br so Se has lesser ionization energy than Br.

ii) is greater than that of tellurium (Te) because the first ionization energy decreases from top to bottom in a group in the Periodic Table. Se and Te are in the same group, and Se is at the top of Te. Hence, Se has a greater first ionization energy than Te.

the electronic configuration of an atom with eight electrons is 1s²2s²2p⁴. the orbital diagrams are shown in the figure.

as per the hunds rule:

1. electrons tend to avoid being in the same orbital as per as practicable.

2. electrons in different orbitals of the same energy will have their spin parallel.

this can be illustrated from the multiplicity of the orbitals of the atom. as there are four electrons in the p orbital and p orbital has 3 sub-shells. the electrons can be fed in different ways as shown in the figure but the correct orbital diagram will be as per the hunds rule.