Further evidence for the existence of energy levels

Question 1

How does the study of first ionisation energy values give further evidence for the existence of energy levels? Use a K atom to explain this.

Answer 1

1. When removing the outermost electron in potassium the first ionisation energy value is low. This has the lowest ionisation energy value since the electron in the 4s sublevel is easiest to remove.
2. The second electron is harder to remove since this electron is being removed from the K+ ion. It now has the same electron config. as argon and the filled outer energy sublevel (3p^6) has extra stability.

The huge increase in the value of the second ionisation energy compared with the first suggests that these electrons must be closer to the nucleus and thus experience less shielding.

Question 2

Define the second ionisation energy

Answer 2

It is the enrgy required to remove an electron from an ion with one positive charge in the gaseous state i.e. the energy required to carry out the following:
X+(g) —> X2+(g) + e-

Question 3

Summarise the general points from the study of the removal of electrons from potassium (1 (2) + 1)

Answer 3

1. There is a steady increase in ionisation energy values as electrons are removed.
   This happens as:
   a) the size of the positive charge on the ion increases as each electron is removed. The greater attraction between the positive nucleus and the remaining electrons is greater.
   b) A positive ion is smaller than the neutral atom. The electrons remaining behind in the positive ion are closer to the nucleus and are more strongly attracted to the nucleus.
2. There is a large increase in ionisation energy whenever an electron is removed from a new energy level and a reasonably substantial increase in the case of a new sublevel because filled sublevels have extra stability.

Question 4

Why is there a steady increase in ionisation energy values as electrons are removed? (2)

Answer 4

1. There is a steady increase in ionisation energy values as electrons are removed.
   This happens as:
   a) the size of the positive charge on the ion increases as each electron is removed. The greater attraction between the positive nucleus and the remaining electrons is greater.
   b) A positive ion is smaller than the neutral atom. The electrons remaining behind in the positive ion are closer to the nucleus and are more strongly attracted to the nucleus.