A-LEVEL CHEMISTRY: 3.2.1: Periodicity PMT & CR

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 or d Blocks.
This is According to which Orbitals the Highest Energy Electrons are in.

Question 3

As you go Across Period, Atomic Radius…

Answer 3

Decreases.

Question 4

As you go Across a Period, Atomic Radius ___. Why is this?

Answer 4

Decreases. This is Because the Increased Number of Protons Creates More Positive Charge, Increasing the Attraction for Electrons, thus Pulling the Shells Further Inwards.

Remember that Atoms in the Same Period have the Same Number of Shells.

Question 5

As you go Across a Period, there is a General Trend that 1st Ionisation Energy…

Answer 5

Increases.

Question 6

As you go Across a Period, there is a General Trend that 1st Ionisation Energy Increases. Why is this?

Answer 6

This is Due to the Increasing Number of Protons, as the Electrons are being Added to the Same Shell.

Question 7

As you go Across a Period, there is a General Trend that 1st Ionisation Energy Increases. However, there is a Small Drop Between ___ & ___. Why is this?

Answer 7

Mg, Al. This is Because Mg has its Outermost Electrons in the 3s Sub-Shell, whereas Al is Starting to Fill the 3p Sub-Shell.
Hence, Al’s Outermost Electrons are Slightly Easier to Remove than Mg’s, because the 3p Electrons are Higher in Energy.

Magnesium (Mg) has 12 Electrons. The first 10 Electrons fill the 1s, 2s, and 2p Sub-Shells (Lowest Energy Orbitals). After that, the next two Electrons go into the 3s Sub-Shell, which is the next Lowest Energy Level.
Aluminium (Al) has 13 Electrons. Like Mg, the first 12 Electrons Fill the Same Sub-Shells (1s, 2s, 2p, 3s). But the 13th Electron Cannot go into the 3s Sub-Shell, since it’s already Filled. So, it goes into the next Available Sub-Shell, the 3p Sub-Shell.
Because the 3p Sub-Shell is at a Higher Energy Level than the 3s, the Outer Electron in Al is Easier to Lose Compared to the Outer Electron in Mg.

Question 8

There is a Small Drop in 1st Ionisation Energy Between ___ & ___. Why is this?

Answer 8

Phosphorus, Sulfur. This is Because Sulfur’s Outermost Electron (in the 3p Sub-Shell) Pairs Up with Another Electron when Phosphorus Gains an Electron to Form an Ion.
When the Electrons Pair Up, there is a Slight Repulsion Between the 2 Negatively Charged Electrons, which Makes the Second Electron Easier to Remove.