Periodicity U1.B

Question 1

Covalent
radius

Answer 1

Decreases along period because:
- nuclear charge increases, pulling electrons closer to nucleus.

Increases down a group because:
- the number of occupied electrons shells increases (screening effect)

Question 2

Ionisation
energy

Answer 2

Increases along period because:
- nuclear charge increases and atomic size decreases so
electrons are held with a greater force.

Ionisation decreases down a group because:
- Outer electrons are increasingly farther away from nuclear attraction
- AND there is a screening effect (or shielding effect) due to electrons on inner shells.

note: some require more energy because it involves the
removal of an electron from an electron shell which is closer
to nuclear AND the electron is less shielded from the
nucleus.

Question 3

Electronegativity

Answer 3

Trends are same as
that of ionisation
energy
(decreasing down and
increasing along)

Question 4

Pure
Covalent
Bonds

Answer 4

Shared pair of outer electrons, electrostatically attracted to positive nuclei of 2 atoms.

Exist between 2 atoms of the
same electronegativity.

No ionic character at all.
E.g. diatomic molecules

Question 5

Trends in ionisation enthalpy

Answer 5

First ionisation enthalpy of an element is the amount required to remove one mole of electrons from one mole of isolated gaseous atoms of the element.
On graph they follow the order of groups, with the noble gases being the highest points (He,Ne,Ar,Kr,Xe)

Question 6

Shielding effect effect

Answer 6

Atomic radius increases

Ionisation energy decreases

Electronegativity decreases