1B Periodicity

Question 1

Define:
First ionisation energy of an element.

Answer 1

The energy required to remove one mole of gaseous electrons from one mole of gaseous atoms.

Question 2

Define:
Electronegativity

Answer 2

The measure of the attraction an atom has for bonding electrons.

Question 3

Trend - across a period:
Electronegativity
Explain.

Answer 3

Electronegativity INCREASES across a group.
As the nuclear charge INCREASES.

Question 4

Trend - down a group:
Electronegativity
Explain.

Answer 4

Electronegativity DECREASES down a group.
As there is an INCREASE in the shielding effect due to an INCREASED number of FULL inner electron shells, reducing the effective nuclear charge attracting the outer electrons to the nucleus.

Question 5

Trend - down a group:
First ionisation energy.
Explain.

Answer 5

Decrease in first ionisation energies down a group because:
- outer electrons are further away from nucleus.
- there is increased screening effect due to more inner electron shells, reducing the effective nuclear charge attracting outer electrons.

Question 6

Trend - across a period:
First ionisation energy.
Explain.

Answer 6

Increase in first ionisation energies across a period because:
- outer electrons are closer to the nucleus.
- there is increased nuclear charge (no increased shielding effect, as no increase in number of inner electron shells).

Question 7

Trend - across a period:
covalent radius (atomic size).
Explain.

Answer 7

Decrease in covalent radius across a period because:
- the nuclear charge increases (with no additional inner electron shells added to shield the nuclear charge).

Question 8

Trend - down a group:
Covalent radius (atomic size).
Explain.

Answer 8

Increase in atomic radius down a group because:
- additional inner electron shells added as you move down the group (so the outer electrons are further from the nucleus).
- there is increased screening effect due to more inner electron shells, reducing the effective nuclear charge attracting outer electrons.

Question 9

Melting points increase as you go down Group 7 because….

Answer 9

….there are more electrons in the diatomic molecules creating more temporary dipoles. = stronger LDF forces of attraction.
=more energy to separate molecules.
=higher mpts!

Question 10

What happens to the nuclear charge as you go across a Period?

Answer 10

Nuclear charge increases.

Question 11

Define the term “covalent radius”.

Answer 11

It is half the distance between the centres (nuclei) of 2 bonded atoms.

Question 12

Is the first ionisation energy an exothermic or endothermic process?

Answer 12

Energy is always required to remove electrons. The process is ENDOTHERMIC.

Question 13

Why is the second ionisation energy of an element always greater
than the first ionisation energy?

Answer 13

In the second ionisation energy negative electrons are being
removed from positive ions rather than neutral atoms.
= the positive ion has a greater attraction for the electrons.
= more energy is needed to remove the second mole of electrons.

Question 14

Name the most electronegative atom.

Answer 14

Fluorine (4.0)

Question 15

Name the least electronegative atom.

Answer 15

Caesium.