Improved Model: Sub-shells - Atomic Structure (3.2)

Question 1

Explain the trend in ionisation energy down a group

Answer 1

• Atomic radius & shielding increases down a group
• Therefore, less energy is required to remove an electron
• So ionisation energy should decrease down a group

Question 2

What is the trend of ionisation energies of group 1 elements?

Answer 2

Decrease in ionisation energy down group 1

Question 3

Explain how ionisation energy changes down a group in terms of atomic radius

Answer 3

• Atomic radius increases down a group
• Outer electron further from nucleus
• Electrostatic attraction is decreased
• Less energy is required to remove outer electron

Question 4

Explain how ionisation energy changes down a group in terms of shielding

Answer 4

• Shielding increases down a group
• More repulsion between inner & outer electrons
• Less energy required to remove outer electron

Question 5

Explain the trend in ionisation energy across a period

Answer 5

• Atomic radius decreases & shielding stays similar across a period
• Therefore, more energy is required to remove an electron
• So ionisation energy should increase across a period

Question 6

Explain how ionisation energy changes across a period in terms of atomic radius

Answer 6

• Decreases across a period
• Outer electron held more strongly by nucleus
• Requires more energy to remove outer electron from atom

Question 7

Explain how ionisation energy changes across a period in terms of shielding

Answer 7

• Fill same outer energy level across a period

- No noticeable effect

Question 8

Describe the general trend for 1st ionisation enthalpies of period 2 elements

Answer 8

General increases in 1st ionisation enthalpies of period 2 elements except B & O

Question 9

Describe the general trend for 1st ionisation enthalpies of period 3 elements

Answer 9

General increases in 1st ionisation enthalpies of period 3 elements except Al & S

Question 10

Why are there exceptions to the trends in 1st ionisation enthalpies of period 2 & 3 elements?

Answer 10

Their electronic configurations

• B & Al only have 1 electron in the outer energy level/p sub shell, therefore it is easy to remove an electron from these atoms
• O & S have 4 electrons in their p sub levels (if 1 electron lost, it is lost easily as there is one in each orbital so the electron configuration is stable)

Question 11

Name the 4 sub-levels

Answer 11

s, p, d, f

Question 12

Max. no. of electrons in s sub-level

Answer 12

2

Question 13

Max. no. of electrons in p sub-level

Answer 13

6

Question 14

Max. no. of electrons in d sub-level

Answer 14

10

Question 15

Max. no. of electrons in f sub-level

Answer 15

14

Question 16

What does the block (s,p,d,f) in the periodic table tell you about an atoms electronic configuration?

Answer 16

The block of the periodic table tells you in which sub-level an atom has its outermost electron

Question 17

Why does Boron not follow the general upwards trend of ionisation enthalpies of period 2 elements?
Explain the reason for this change from Be -> B

Answer 17

• The outer electron in B is in the 2p sub-level
• In Be it is in the 2s sub-level
• The 2p sub-level is slightly further from the nucleus
• So electrostatic attraction from the nucleus decreases
• The 2p sub-level is slightly shielded by the 2s sub-level so repulsion increases
• Slightly less energy is required to remove the outer electron