Ionisation Energy

Question 1

What is the first ionisation energy?

Answer 1

Energy needed to remove 1 mole of electrons from 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions

e.g. Na(g) —> Na+(g) + e-

Question 2

What is the second ionisation energy?

Answer 2

Energy needed to remove 1 mole of electrons from 1 mole of gaseous 1+ ions to form 1 mole of 2+ ions

eg O+(g) —> O2+(g) + e-

Higher ionisation energy means it is more difficult to form a + ion as there is a high attraction between the nucleus and the electron.

Question 3

What affects ionisation energy?

Answer 3

Nuclear charge: more protons means stronger attraction so electrons are more difficult to remove

Distance from nucleus: electrons closer to the nucleus are more strongly attracted.

Shielding: More electrons between the nucleus and the outer electrons reduce the attraction

Question 4

Trend in ionisation down the group

Answer 4

Trend down group: 1st ionisation energy decreases

Explanation: Electron being removed is further from the nucleus More shielding because there are more electrons
between the nucleus and the electron being removed

Question 5

Trends in ionisation across a period

Answer 5

General trend across period: 1st ionisation energy increases

Explanation: Nuclear charge (number of protons increases) Same shielding because the electrons are being removed from the same shell