Topic 1: Atomic Structure

Question 1

Definitions I:
(a) Atomic structure
(b) Shell
(c) Sub-shell

Answer 1

Definitions I:
(a) The arrangement of sub-atomic particles within an atom (p, n, and e⁻).
(b) Energy level holding electrons around the nucleus, defined by principal quantum number (n).
(c) One or more orbitals in the same shell which have the same energy levels.

Question 2

Definitions II:
(a) Isotope
(b) First ionisation energy
(c) Orbital

Answer 2

Definitions II:
(a) Atoms of an element with same proton number but different neutron numbers.
(b) Energy required to remove 1 mole of e⁻ from 1 mole of gaseous atoms of an element to form 1 mole of gaseous ions with a single positive charge.
(c) Volume of space of an atom where an electron is most likely to be found.

Question 3

What are the relative charges and masses of:
(a) Protons and neutrons? [1 Mark]
(b) Electrons? [1 Mark]

Answer 3

(a) Protons: +1, 1 u; neutrons: 0, 1 u (1 mark)
(b) Electrons: -1, 1/1836 u (1 mark)

Question 4

How do protons, neutrons, and electrons move in an electric field? [3 Marks]

Answer 4

Protons to negative plate (1 mark)
Neutrons no deflection (1 mark)
Electrons to positive plate (1 mark)

Question 5

How many protons, neutrons, electrons are in ²⁴Mg²⁺ and what is its electronic configuration? [3 Marks]

Answer 5

Protons: 12, neutrons: 12, electrons: 10 (2 marks)
Configuration: 1s² 2s² 2p⁶ (1 mark)

Question 6

Why does atomic radius decrease across Period 2? [2 Marks]

Answer 6

Nuclear charge increases (1 mark)
Same shielding, smaller radius (1 mark)

Question 7

What are the number of electrons in s, p, d sub-shells and their energy order up to 4s? [2 Marks]

Answer 7

s: 2, p: 6, d: 10 electrons (1 mark)
1s < 2s < 2p < 3s < 3p < 4s (1 mark)

Question 8

What are the shapes of s and p orbitals? [2 Marks]

Answer 8

s: spherical (1 mark)
p: dumbbell (1 mark)

Question 9

What is the equation for:
(a) The first ionisation of Na? [1 Mark]
(b) The second ionisation of Na? [1 Mark]

Answer 9

(a) Na(g) → Na⁺(g) + e⁻ (1 mark)
(b) Na⁺(g) → Na²⁺(g) + e⁻ (1 mark)

Question 10

How do successive ionisations show Ne’s group in the Periodic Table? [2 Marks]

Answer 10

Large jump after 8th ionisation (1 mark)
Group 18, 8 valence electrons (1 mark)

Question 11

Why do ¹⁴N and ¹⁵N have the same chemical properties but different densities? [2 Marks]

Answer 11

Same proton number, electron configuration (1 mark)
More neutrons in ¹⁵N, higher density (1 mark)

Question 12

What is the electrons-in-boxes notation for N (Z=7)? [2 Marks]

Answer 12

1s² ↑↓, 2s² ↑↓, 2p³ ↑ ↑ ↑ (2 marks)