Atomic Structure

Question 1

What are the 2 factors affecting the ionisation energy?

Answer 1

• nuclear charge
• shielding effect

Question 2

Explain the trend in ionisation energy across the period

Answer 2

-As number of protons increases, nuclear charge increases.

-As successive electrons are added to the same outermost electron shell, the shielding
effect is approximately the same

-Effective nuclear charge increases.

-Forces of attraction between the nucleus and the outermost electron increases.

-More energy is needed to remove the outermost electron.

-Thus first IE generally increases across a period

Question 3

Explain the trend in ionisation energy down the group.

Answer 3

• As number of protons increases, nuclear charge increases
• As number of principal quantum shell increases, shielding effect increases significantly.

-the outermost electron is further away from the nucleus

• attraction between the nucleus and the outermost electron decreases.

-less energy is needed to remove the outermost electron

• the first IE decreases down a group.

Question 4

Explain for the decrease in IE between elements with ns^2 and ns^2np^1 configurations

Answer 4

-write down the electronic configuration of both elements
- less energy is needed to remove the 2p electron from a higher energy 2p subshell.

Question 5

Explain the decrease in IE between group 15 and 16 elements

Answer 5

• group 15 elements have an electronic configuration of ns² np_x¹ np_y1 np_z¹
• group 16 elememts have an electronic configuration of ns² np_x² np_y1 np_z¹
• less energy is required to remove the paried np_x electron as it experiences inter electronic repulsion.

Question 6

Explain the IE between periods.

(take example to be Na and Ne)

Answer 6

• As Na has one more proton than Ne, nuclear charge increases
• As Na has one more principal quantum shell than Ne, shielding effect increases significantly.
• The outermost electron is further away from the nucleus in Na.
• Attraction between the nucleus and the outermost electron decreases in Na
• Less energy is required to remove the 3s electron in Na.
• The first IE decreases significantly from Ne to Na

Question 7

Why do anions have a larger radii than their respective atoms?

Answer 7

• There are more electrons than protons in the anion
• The net attractive force on the valence lectrons by the nucleus decreases

Question 8

How does id-id attraction come about?

Answer 8

-In an atom or molecule, the elctrons are constantly moving.
- At any moment, there can be an asymmertrical electron desnsity around a molecule.
- this results in an instantaneous dipole formed.
- this instantaneous dipole will induce another dipole on its neighbouring molecule.
- the electrostatic attraction between these fluctuating dipoles are known as id-id attraction.

Question 9

How does pd-pd attraction arise?

Answer 9

• Polar molecules have a permamenent net dipole.
• The oppositely charged ends of the dipoles attract each other.
• This attraction is known as the pd-pd attraction.