A-LEVEL CHEMISTRY: 3.2.1: Periodicity (ChemRevise & PMT)

Question 1

What is ‘Periodicity’?

Answer 1

Periodicity is the Repeating Pattern of Chemical or Physical Properties, Going Across the Periods.

Question 2

Elements are Classified as…
What is this According to?

Answer 2

s, p, d, f Blocks.
According to which Orbital the Highest Energy Electrons are in.

Question 3

As you go Across Period, Atomic Radius…

Answer 3

Decreases.

Question 4

What is the General Trend for Atomic Radius across a Period? Explain it. (4)

Answer 4

Decreases.

Because:
-Nuclear Charge increases (more Protons)

-same number of Electron Shells across a Period, so similar Shielding

-Increased Nuclear Attraction pulls Outermost Electrons closer to the Nucleus

Question 5

What is the General Trend for First Ionisation Energy across a Period?

Answer 5

Increases.

Question 6

What is the General Trend for First Ionisation Energy across a Period? Explain it. (5)

Answer 6

Increases.

Because:
-Nuclear Charge Increases (more Protons)

-Outermost Electrons experience stronger Nuclear Attraction

-Shielding remains similar

-so more Energy is required to remove Valent Electrons.

Question 7

What are the two exceptions to the General Trend in First Ionisation Energy across Period 3? (2)
Explain them. (6)

Answer 7

• Al lower than Mg
  Because:
  -Al valent electron is in p-orbital (higher energy)

-Further away from the Nucleus

-so requires less Energy to remove from the Atom

• S lower than P
  Because:
  -S Valent Electrons are paired in p-orbital

-so they naturally Repel each other

-so less Energy is needed to remove from the Atom

Question 8

Explain the first exception in the trend for First Ionisation Energy across a Period. (4)

Answer 8

-between Group 2 & 3, eg Al lower than Mg

Because:
-Al valent electron is in p-orbital (higher energy)

-Further away from the Nucleus

-so requires less Energy to remove from the Atom

Question 9

explain the second exception in the trend for First Ionisation Energy across Period 3. (4)

Answer 9

-S lower than P

Because:
-S Valent Electrons are paired in p-orbital

-so they naturally Repel each other

-so less Energy is needed to remove from the Atom

Question 10

As you go Across a Period, First Ionisation Energy…

Answer 10

GENERALLY Increases

Question 11

Explain the Trend in Melting & Boiling Points across Period 3 (4)

Answer 11

-Metals (Groups 1-3) (Na, Mg, Al): MP & BP Increase. Stronger Metallic Bonds, as Charge & number of Delocalised Electrons Increase

-Silicon, Si (Group 4): Highest MP & BP, Giant Covalent Structure

-Simple Molecular Structures (Groups 5-7)(P, S, Cl) : MP & BP Decrease, due to weak Van der Waals Forces. CLUSTERS.

-Noble Gases (Group 8)(Argon, Ar): Lowest MP & BP. Monatomic, weak Van der Waals Forces