[Unit 1.5] | More On Electron Arrangement

Question 1

How many electrons are there in an orbital?

Answer 1

2: a pair with opposite spins.

Question 2

How many orbitals/electrons are in each sub-shell?

Answer 2

• S: 1 orbital, 2 electrons
• P: 3 orbitals, 6 electrons
• D: 5 orbitals, 10 electron
• F: 7 orbitals, 14 electrons
• Formula: 2n-1 orbitals

Question 3

Which subshells are present in each shell?

Answer 3

• 1: s
• 2: s, p
• 3: s, p, d
• 4: s, p, d, f

Question 4

What must happen within a subshell before electrons can be paired in orbitals?

Answer 4

Each orbital must have 1 electron before pairs can form. This is to minimise electron repulsion.

Question 5

What does the Aufbau principle state?

Answer 5

Electrons fill lower energy orbitals (ones closer to the nucleus) first.

Question 6

Why does the 4s orbital fill before the 3d orbital and why does it also empty before 3d?

Answer 6

• It fills first because it is closer to the nucleus and is therefore lower energy.
• However, when it fills it becomes higher energy than 3d.