Trends in the periodic table

Question 1

Atomic Radius - across a period

Answer 1

Number of protons increases going across the periodic table (but the number of electron shells remains the same). Hence, the electrostatic force of attraction between the negative outer electrons and the positive nucleus increases. Hence, the atomic radius decreases.

Question 2

Atomic radius - down a group

Answer 2

Number of electron shells increases, this results in a greater distance between the centre of the nucleus and the outermost electron. Hence, atomic radius increases moving down a group.

Question 3

Ionisation Energy - across a period

Answer 3

Number of protons increases but the number of electron shells remains the same. Hence, there is an increased electrostatic force of attraction between the positively charged nucleus and the negative valence electron (I.e. core charge/effective nuclear charge increases), and the atomic radius decreases. Thus, more energy is required to remove the valence electron (i.e. ionisation energy increases across a period.

Question 4

Ionisation Energy - down a group

Answer 4

Number of electron shells increases, this results in a larger atomic radius and, valence electrons experiencing a greater shielding effect (repulsion) from inner shell electrons. This decreases the electrostatic force of attraction between the positive nucleus and the negative valence electron. Hence, less energy is required to remove a valence electron. Thus, ionisation energy decreases moving down a group.

Question 5

Electronegativity - across a period

Answer 5

Number of protons increases, but the number of electron shells remains the same. The electrostatic force of attraction between the positive nucleus and the negative bonding pair of electrons from a neighbouring atom increases. Hence there is a greater ability to attract a bonding pair of electrons. Thus, the electronegativity increases moving across a period.

Question 6

Electronegativity - down a group

Answer 6

Number of electron shells increases, this results in a larger atomic radius. This decreases the electrostatic force of attraction between the positive nucleus and negative bonding pair of electrons from a neighbouring atom. Hence, it is harder to attract a bonding pair of electrons. Thus, electronegativity decreases moving down a group.