Periodicity and I.E

Question 1

definition of ionisation energy

Answer 1

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

Question 2

second ionisation energy

Answer 2

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

Question 3

what do first i.e equations form?

Answer 3

all first i.e equations always form one mole, no matter what group it’s in, always forming +1 ions

Question 4

what happens to the ionisation energy every time you pull off an electron?

Answer 4

every time you pull off an electron, results in more protons compared to electrons so they’re held closer to the nucleus so there’s a greater pull hence more ionisation energy needed to pull off electrons as they’re closer so i.e will be greater

Question 5

trend for first i.e. as u go down the group

Answer 5

as you go down the group the first I.E decreases

Question 6

why does the I.E. decrease down the group?

Answer 6

as we go down the group, atomic radius increases, as well as increased shielding. this results in the nuclear attraction to the outer electron decreasing. so as we go down the group, less energy is required to remove the outer e- hence first i.e. decreasing as we go down the group

Question 7

trend across a period of i.e.

Answer 7

periodicity of ionisation energy increases

Question 8

across a period, why does the atomic radius decrease instead of increase?

Answer 8

because as you go across a period, you add an electron as protons increase so nuclear attraction increases as electrons pulled in more (nuclear charge increases) / attracts electrons more strongly hence decreasing the radius

Question 9

describe the trend across a period of the I.E.

Answer 9

atomic radius decreases, but electron shielding stays the same. however the nuclear attraction increases as a result, so energy required to remove outer e- increases, resulting in the first i.e. increasing as you go across a period

Question 10

why is there always a dip in I.E. between elements of group 2 and 3
eg B in grp 3 and Be in grp 2?

Answer 10

• boron’s outer e- is in 2p and beryllium’s is in 2s
• 2p is higher in energy than 2s
• less energy is required to remove the 2p electron
• meaning there’s a lower i.e. in group 3

Question 11

why is there a dip in I.E. of elements in group 5 and group 6?
eg O in grp 6 and N in grp 5

Answer 11

though both in 2p:
- oxygen has paired electrons in one of its 2p orbitals
- because paired electrons repel, less energy is required to remove the paired e-
- hence oxygen has a lower 1st I.E. compared to nitrogen