7.2 Ionisation Energies

Question 1

Define first ionisation energy

What unit?

Answer 1

The energy required to remove one electron from each atom in one mol of gaseous atoms to form one mol of gaseous 1+ ions

KJmol -1

Question 2

Define second ionisation energy

Answer 2

The energy required to remove an electron from each atom in one mol of gaseous 1+ ions to form one mol of gaseous 2+ ions

Question 3

what electron is lost first?

Answer 3

Electron in the highest energy level / shell that experiences least nuclear attraction

Question 4

3 Factors affecting ionisation energy and why

Answer 4

ATOMIC RADIUS - greater distance between nucleus and electron = less attraction = lower ionisation energy

NUCLEAR CHARGE - the more protons in the nucleus = greater attraction = higher ionisation energy

SHIELDING - inner electrons repel outer electrons causing shielding, reducing attraction

Question 5

Why is the second ionisation energy higher than the first?

Answer 5

Because after the first electron is removed the remaining electrons at pulled closer to the nucleus, increasing the nuclear attraction

Question 6

Ionisation energys allow us to predict?

Answer 6

The number of electrons in outer shell
The elements group
The elements identity

Question 7

What do larger differences in the energies show?

Answer 7

The Jump from outer shell to inner shell

Question 8

Trend in first ionisation energy down a group?

Why?

Answer 8

Decreases down a group because:

Atomic radius increases

More inner shells so shielding increases

Nuclear attraction on outer electrons decreases

Question 9

Trend in first ionisation energies across a period?

Answer 9

Increases across a period because:

Nuclear charge increases

Same shell = similar shielding

Atomic radius decreases

Question 10

Trend in periods 2 and 3?

Answer 10

There is a general increase across both period 2 and period 3. However they both fall in the same two places due to sub-shells, their energies and how orbitals fill with electrons

Question 11

What are the falls in period 2 and what do they mark?

Answer 11

Be - B marks the start of the filling of the 2P sub shell

N - O marks the start of the electron pairing in the so originals of the 2P sub-shell

Question 12

How does the pairing of orbitals in sub shells cause fall in ionisation energy?

Answer 12

The paired electrons repel and make it easier for them to be removed