Atomic Structure

Question 1

I.E trend of 2 elements in the same group

Answer 1

Down the group, the number of protons increases and hence nuclear charge increases. There is an additional electronic shell, hence screening effect increases. The valence electrons are further away and less strongly attracted by the nucleus. Less energy is required to remove the valence electrons, hence first ionisation energy decreases down a group.

Question 2

I.E. trend of 2 elements in the same period

Answer 2

Across the period, the number of protons increases and hence nuclear charge increases. Additional electrons are added to the same shell, hence screening effect remains approximately constant. Valence electrons are closely and more strongly held to the nucleus. More energy is required to remove the valence electrons, hence first ionisation energy decreases down a group.

Question 3

Exceptions of I.E. trend across the period (there are 2)

Answer 3

1. When electrons are removed from a different subshell, which affects the distance from nucleus
2. When one element has a doubly filled p orbital and the other doesn’t, which causes inter electron repulsion between paired electrons and requires less energy to remove

Question 4

I.E. trend for successive electrons removed from same element

Answer 4

Number of protons is the same hence nuclear charge remains constant. Screening effect decreases and remaining electrons are held more strongly and closer to the nucleus. More energy is required to remove remaining electrons