Periodicity

Question 1

What is periodicity?
(2 marks)

Answer 1

Pattern in the change in the properties in a row of elements repeated in the next row

Question 2

Why does Aluminium deviate from the trend in the 3rd period?

Answer 2

• It has an outer electron in the 3p orbital rather than the 3s orbital.
  -3p has a slightly higher energy than the 3s orbital
• Electron is found to be further away from the nucleus
• Additional shielding provided by the 3s electrons

Question 3

Atomic Radius

Answer 3

Decreases across a period
Number of protons increases/ greater nuclear charge
Electrons pulled closer to the nucleus making atomic radius smaller
Extra electrons elements gain across a period are added to the same energy level so across period elements experience the same/similar shielding.

Question 4

P4, S8, Cl2, Ar

Answer 4

• Simple Molecular substances
• Van der Waals are weak and easily overcome: low melting point
• More atoms in molecule = stronger Van Der Waals forces
• S8 = biggest molecule: higher melting point than P4 and Cl2
• Ar has a very low melting point because it exists as individual/monatomic: Van der Waals

Question 5

Sodium, Magnesium, Aluminium

Answer 5

• Melting point increases across a period because the metal-metal bonds get stronger
• Metal ions have increasing positive charge
• Increasing number of delocalised electrons
• decreasing ionic radius

Question 5

Melting points across period 3

Answer 5

• Increase from sodium to silicon(because metals + giant covalent)
• Decrease from silicon to argon(because simple molecular)

Question 6

Silicon

Answer 6

• Macromolecular
• Tetrahedral structure
• Strong covalent bonds linking all its carbons together
• lots of energy required to break bonds: silicon has a high melting point