Atomic Structure

Question 1

Explain why atomic radius increases down the group

Answer 1

The number of electronic shells increases, which leads to an increase in screening effect, and each successive element has its valence electrons in a shell with a higher principal quantum number.
Hence, valence electrons are increasingly further away from the nucleus, despite the increase in nuclear charge.

Question 2

Explain why first ionisation energy decreases down the group

Answer 2

1. As the number of electron shells increases, there is an increase in screening effect, and each successive element has its valence electrons located in a shell with higher principal quantum number.
2. Hence, valence electrons are increasingly further away from the nucleus and are less strongly attracted to the nucleus, despite the increase in nuclear charge.
3. Smaller amount of energy is required to remove the valence electrons.

Question 3

Why does atomic radius decrease across the period

Answer 3

1. Electrons are added to the same valence shell across the period, hence screening effect remains relatively constant
2. Increase in nuclear charge outweighs the negligible increase in screening effect
3. Thus effective nuclear charge increases across the period.
4. There are stronger electrostatic forces of attraction between the nucleus and its valence electrons, so valence electrons are progressively pulled closer to the nucleus

Question 4

Why does first ionisation energy increase across the period

Answer 4

1. As electrons are added to the same valence shell across the period, screening effect remains approximately constant.
2. Increase in nuclear charge outweighs negligible increase in screening effect
3. Effective nuclear charge increases across the period
4. There are stronger electrostatic forces of attraction between the nucleus and the valence electrons, thus more energy is required to remove the valence electron.

Question 5

Angle of deflection of a particle is directly proportional to

Answer 5

Its charge-to-mass ratio

Question 6

Isotopes

Answer 6

Atoms of the same element with the same number of protons but a different number of neutrons.

Question 7

Orbital

Answer 7

A region of space around the nucleus where there is a 90% probability of locating the electron in this region.