Periodicity

Question 1

Explain the Trend of Atomic Radius across a period

Answer 1

Atomic Radius Decreases as you across a period

• More proton rich nucleus as you across a period
• Similar Shielding for all elements in that period

This means that the forces of attraction between the outermost orbital and nucleus increases pulling the orbital in closer

Question 2

Explain the trend of Atomic Radius Down a group

Answer 2

Atomic radius increases as you go down a group
- More shielding due to extra electron shells
This means the nucleus and the outermost orbital are futher apart

Question 3

Explain the Trend in Ionisation Energy across period 3 (include exceptions)

Answer 3

General Increase in ionisation energy

• More proton rich nucleus as you across a period
• Similar Shielding for all elements in that period

This means that the forces of attraction between the outermost orbital and nucleus increases so more energy is required to overcome these forces to remove an electron from the outer shell

Sulphurs ionisation energy is slightly less that of phosphorus,
Outer electrons in 3p orbitals begin to pair
within sulphurs outermost orbital electron-electron repulsion between the two means that less energy is required to remove an electron, then phosphorus’ one outer orbital electron.

The outermost electron in aluminium sits in a higher energy orbital slightly further from the nucleus then the outer electron in magnesium. This results in less energy required to remove the outermost electron from Aluminium

Question 4

Explain the Trend of Metallic Melting points across period 3

Answer 4

General Increase in melting point
Similar Shielding
Metal ions across a period have an increasing positively charged nucleus,increasing the number of delocalised electrons, and decreasing the ionic radius
This produces an increasing force of attraction between the sea of delocalised electrons and the nuclei.
Producing a stronger metallic bond.
(Al is only slightly higher then mg)
(mg is double Na)

Question 5

Explain the trend in Covalent Melting Points in period 3

Answer 5

Silicon has the highest melting point in period 3, it has a giant covalent structure, with 4 bonds per atom, producing many strong covalent bonds and a larger amount of energy is required to overcome these strong covalent bonds.

Phosphorus has the formula P4, It has only a simple molecular structure, that takes less energy to overcome due to only weaker VDW forces between the atoms

Sulphur has the formula S8, It’s melting point is higher the phosphorus due to a larger simple molecular structure producing larger VDW forces between the atoms

Chlorine has the formula Cl2 Lower melting point then S8 & P4 due to a smaller simple molecular structure producing smaller VDW forces

Argon has the formula Ar it has the lowest melting point due to only existing as an individual atom producing much smaller VDW forces.

Question 6

Answer 6

Phosphorus

Large jump in ionisation energy after 5e- has been removed

5 Electrons in Valence Shell

This is when the electron is being removed from the 2nd principle energy level