Ionisation energy

Question 1

The electronic configuration of potassium is 2,8,8,1. Explain why the second ionisation energy of potassium greater than its first ionisation energy.

Answer 1

The first electron to be removed from potassium is in the fourth shell (valence shell) whereas the second electron to be removed is in the third shell, which is closer to the nucleus. As such, more energy needs to be absorbed to overcome the stronger attraction between the second electron and the nucleus.

Question 2

What does the electronic configuration of an atom refer to?

Answer 2

The electron configuration of an atom refers to the way its electrons are arranged in the atom. You would recall that the electron configuration of carbon atom (with 6 electrons) is 2.4 - two in the first shell and 4 in the second shell.

Question 3

How do scientists actually know how these electrons are arranged in an atom?

Answer 3

The study of ease with which atoms lose electrons provides useful information about the arrangement of electrons.

Question 4

The amount of energy needed to remove one electron from a gaseous atom is known as its _________________.

Answer 4

Ionisation energy (IE)

Question 5

What is the equation for the first ionisation energy of carbon?

Answer 5

The first ionisation energy of carbon is the energy required to remove the first electron from one neutral carbon atom.

Question 6

It can be observed that the ionisation energy increases/decreases (choose one) as the ionisation increases (i.e. successive loss of electrons).

Answer 6

Increases

Question 7

The table gives all the 6 ionisation energies of carbon.

Ionisation number 1st:
ionisation energy/kJ mol to the power of -1 (1087)

Ionisation number 2nd:
ionisation energy/kJ mol to the power of -1 (2353)

ionisation number 3rd:
ionisation energy/kJ mol to the power of -1 (4621)

Ionisation number 4th:
ionisation energy/kJ mol to the power of -1 (6223)

Ionisation number 5th:
ionisation energy/kJ mol to the power of -1 (37831)

Ionisation number 6th:
ionisation energy/kJ mol to the power of -1 (47277)

Describe the successive ionisation energies data.

Answer 7

It can be observed that the ionisation energy increases as the ionisation number increases (i.e. successive loss of electrons).

Although the increases in IE is generally gradual, there is a sudden large increase between the 4th and 5th IEs.

This implies that there are 2 groups of electrons. The 5th and 6th electrons are closer to the nucleus of the atom, while the 1st to 4th electrons are farther away. This gives rise to the idea of electron shells, thus the 5th and 6th electrons are in the inner shell while the 1st to 4th electrons are the valence electrons.

Question 8

The first 4 ionisation energies of element Z is given as 577, 1820, 2740, 11600 (all measured in kJ mol to the power of -1).

How many valence electrons does an atom of Z have?

A 1
B 2
C 3
D 4

Answer 8

C

Question 9

The first ionisation energy of element S is represented by the equation:

S (g) –> S + (g) + e -

Which is the correct equation for the second ionisation energy of S?

A S (g) –> S 2+ (g) + 2 e -
B 2S (g) –> 2S + (g) + 2 e -
C S+ (g) –> S 2+ (g) + e -
D S+ (g) + e - –> S (g)

Answer 9

C