3.1.1 The Periodic Table + 3.1.1 Ionisation energies

Question 1

how is the periodic table arranged

Answer 1

• by increasing atomic (proton) number
• in periods
• in groups

Question 2

define periodicity

Answer 2

a repeating trend in properties of elements across each period of the periodic table

Question 3

define first ionisation energy

Answer 3

The energy needed to remove 1mol of electrons from 1 mol of gaseous atoms.
X(g) →X⁺(g) + e⁻

Question 4

what factors affect the size of ionisation energy

Answer 4

1. atomic radius
2. nuclear charge
3. electron shielding

Question 5

How does atomic radius affect ionisation energy

Answer 5

The greater the distance between the nucleus and the outer electons the less the nuclear attraction. The force of attraction falls of sharply with increasing distance so atomic radius has a large effect

Question 6

how does nuclear charge affect ionisation energy

Answer 6

The more protons there are in the nucleus of an atom, the greater the attraction between the nucleus the outer electrons.

Question 7

how does electron shielding affect ionisation energy

Answer 7

Electrons are negatively charged and so inner-shell electrons repel outer-shell electrons. This repulsion, called the shielding effect, reduces the attraction between the nucleus and the outer electrons.

Question 8

describe the trend in ionisation energy down a group

Answer 8

Increased nuclear charge BUT more shells and so a larger atomic radius and greater shielding.
This leads to smaller ionisation energies as the attraction for the nucleus is less. (there is a smaller effective nuclear charge)

Question 9

describe the trend in ionisation energy across a period

Answer 9

As you go across a period the shielding is unchanged (the same number of shells) BUT the nuclear charge increases.
Therefore ionisation energy increases as there is a greater attraction for the nucleus. (effective nuclear charge increases)

Question 10

Explain why not all elements follow the trend for across a period for example Be→B and Mg→Al

Answer 10

The ionisation energy drops slightly at this point
Ionisation energy decreases as an electron is removed from the 2p subshell in B rather than the 2s subshell in Be. 2p is higher in energy than 2s.

Question 11

Explain why not all elements follow the trend across a period for example N→O

Answer 11

The 4th electron in the 2p subshell in oxygen becomes paired with the 1st electron in the 2p subshell, now together the paired electrons repel, making it easier to remove the electron resulting in a lower ionisation energy.

Question 12

what element has the highest first ionisation energy

Answer 12

Helium