Periodic Trend In EIectron Configuration And Ionisation Energy

Question 1

what is the periodic trend in electron configuration across period 2?

Answer 1

2s subshell fills followed by 2p subshell

Question 2

what is the periodic trend in electron configuration across period 3?

Answer 2

3s subshell fills followed by 3p subshell

Question 3

what is the classfication of elements into s, p. d and f blocks?

Answer 3

s on the left, p on the right, d in the middle and f block at the bottom

Question 4

what is the first ionisation energy?

Answer 4

the energy required to remove one mole of electrons from one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions

Question 5

why are elements classified to specific blocks?

Answer 5

the highest energy electron is in that orbital (s,p,d or f)

Question 6

what is the trend in first ionisation energy across period 2(general)?

Answer 6

first ionisation energy increases generally
- greater nuclear charge
- similar shielding
- greater nuclear attraction
- atomic radius decreases

Question 7

what is the trend in first ionisation energy across period 3(general)?

Answer 7

first ionisation energy increases generally
- greater nuclear charge
- similar shielding
- greater nuclear attraction
- atomic radius decreases

Question 8

what is the trend in first ionisation energy down a group?

Answer 8

first ionisation energy decreases down a group
- atomic radius increases
- electron shielding increases
- nuclear attraction weakens
- greater nuclear charge

Question 9

where does the first ionisation energies drop in period 2?

Answer 9

• beryllium to boron
• nitrogen to oxygen

Question 10

why does the first ionisation energy drop from beryllium to boron in period 2?

Answer 10

• B electron is removed from 2p
• Be electron is removed from 2s
• 2p electron in B has higher energy than the 2s electron in Be
• so it is easier to remove 2p electron in B compared to 2s electron in Be

Question 11

why does the first ionisation energy drop from nitrogen to oxygen in period 2?

Answer 11

• in N2 and O2 highest energy electrons are in 2p subshell
• in O2, paired electrons in one of the 2p orbitals repel each other = easier to remove electron from oxygen atom compared to nitrogen atom

Question 12

how can you see if the electron is being removed from a different shell?

Answer 12

a large increase in the ionisation energy

Question 13

why does the first ionisation energy drop from phosphorus to sulfur in period 3?

Answer 13

• in P and S the highest energy electrons are in the 3p subshell
• in S, there are paired electrons in one of the 3p orbitals and these repel each other
• so it is easier to remove an electron from the sulfur atom compared to removing one electron from the phosphorus atom

Question 14

why does the first ionisation energy drop from magnesium to aluminium in period 3?

Answer 14

• Mg electron is removed from 3s
• Al electron is removed from 3p
• 3p electron in Al has higher energy that 3s electron in Mg
• so it is easier to remove 3p electron from Al compared to 3s electron in Mg and requires less energy

Question 15

how do you write the first ionisation energy(e.g. for magnesium)?

Answer 15

Mg(g)–> Mg+(g) + e-

Question 16

how do you write the second ionisation energy(e.g. for magnesium)?

Answer 16

Mg+(g) –> Mg2+(g) + e-

Question 17

why is potassium placed immediately after argon in the periodic table?

Answer 17

potassium has one more proton than argon

Question 18

why do successive ionisation energies increase with ionisation number?

Answer 18

• radius decreases
• attraction between the remaining electrons and nucleus increases