Module 1: Periodicity

Question 1

What is periodicity?

Answer 1

Periodicity is the trend in physical & chemical properties of elements across the periodic table.

Question 2

What is the trend in atomic radius across a period (Na-Ar)?

Answer 2

Atomic radius decreases across a period.

Question 3

Why does atomic radius decrease across a period (Na-Ar)?

Answer 3

• The number of protons increases so the positive charge of the nucleus increases.
• Electrons are pulled closer to the nucleus, decreasing atomic radius.
• The addition of extra elements across the period are added to the outer energy level so don’t provide any extra shielding.

Question 4

What is the trend in melting point across a period (Na-Ar)?

Answer 4

Melting point increases from sodium to silicone, but decreases from silicone to argon.

Question 5

Why does melting point increase from sodium to aluminium?

Answer 5

• Sodium, magnesium & aluminium are metals.
• Melting point increases as the metal-metal bonds become stronger.
• The metal ions having increasing positive charge, an increasing number of delocalised electrons & a decreasing atomic radius.

Question 6

Why is there a large increase in melting point from aluminium to silicone?

Answer 6

• Silicone is macromolecular with a tetrahedral structure.
• A large amount of energy is required to break the covalent bonds between the atoms.
• Therefore, silicone has a high melting point.

Question 7

Why does melting point decrease from silicone to argon.

Answer 7

• Phosphorus, sulfur & chlorine are all molecular substances.
• They have weak Van der Waals forces between the molecules that are easy to overcome & so possess a low melting point.
• Sulfur is the largest molecule so has a higher melting point than phosphorus & chlorine.
• Argon has a very low melting point because it is monatomic (exists as individual atoms) & has very weak Van der Waals forces.

Question 8

What is the trend in first ionisation energy across a period (Na-Ar)?

Answer 8

First ionisation energy increases across the period.

Question 9

Why does first ionisation energy increase across a period (Na-Ar)?

Answer 9

• Increasing number of protons.
• Therefore, increasing attraction between the outer electrons & the nucleus.

Question 10

How is the periodic table arranged?

Answer 10

The periodic table is arranged into periods & groups by proton number.