Periodic Table and Trends

Question 1

Atomic radius

Answer 1

• distance from the centre of the nucleus to the outermost electron orbital in an atom
• determined by how strongly these negative outermost electrons are attracted to the positive nucleus

Question 2

Effective Nuclear Charge

Answer 2

• the net positive charge experienced by an electron from the nucleus

Question 3

Trends down a group

Answer 3

Atomic radius increases down a group:

• the outermost electron/s are in a higher energy level, further from the nucleus
• the nucleus is also more positively charged, but the extra shielding from more inner electrons cancels this out –> the effective nuclear charge is the same

Question 4

Trends across a period

Answer 4

Atomic radius decreases across a period:
- electrons are in the same energy level with the same shielding, but as you move along the period, there are more electrons experiencing the same shielding, effective nuclear charge increases

Question 5

Ionic Radius trends

Answer 5

1. Cations are smaller than their parent atoms –> outer electrons have been removed
2. Anions are larger than their parent atoms –> addition of outer electrons
3. Ionic radius increases down a group
4. Ionic radius decrease from groups 1,2 and 13-14
5. Ionic radius decreases from groups 13-17

Question 6

First Ionisation energy

Answer 6

• energy required to remove one electron from one mole of the atom
• the greater the effective nuclear charge, the higher the first Ionisation energy

Question 7

Trend down a group

Answer 7

First Ionisation energies decrease down a group:

• outermost electrons are in a higher energy level, further from the nucleus
• ENC stays the same

Question 8

Trend across a period

Answer 8

First Ionisation energies increase across a period:

- electrons are in the same energy level but the nuclear charge increases, ENC increases also

Question 9

Electronegativity

Answer 9

• the ability of an atom to attract electrons

- determined by ENC but electron configuration needs to be considered

Question 10

Trend down a group

Answer 10

EN decreases down a group:

• outermost electrons are in a higher energy level, further from nucleus
• the nucleus gets more positive but with the same shielding –> ENC is the same

Question 11

Trend across a period

Answer 11

EN increases across a period:

- electrons in the same energy lvel with the same shielding but the NC increases –> ENC increases