Common mistake: Writing electron configurations that violate Hund's rule

Writing electron configurations that violate Hund's rule — partially fill each orbital before pairing

Common mistake: Forgetting that transition metals lose 4s electrons first when forming ions (e.g. Fe²⁺ has configuration [Ar]3d⁶)

Forgetting that transition metals lose 4s electrons first when forming ions (e.g. Fe²⁺ has configuration [Ar]3d⁶)

Common mistake: Concluding a molecule is polar purely because it has polar bonds

Concluding a molecule is polar purely because it has polar bonds — geometry must be asymmetric too

Common mistake: Confusing electronegativity (tendency to attract electrons in a bond) with electron affinity (energy when an isolated atom gains an electron)

Confusing electronegativity (tendency to attract electrons in a bond) with electron affinity (energy when an isolated atom gains an electron)

VCE Units 1–4 · Chemistry

VCE Chemistry — Atomic Structure and Bonding

Atomic structure and bonding form the foundation of all VCE Chemistry. Understanding how electrons are arranged, how atoms combine and why different substances have different properties is essential for every subsequent topic. Exam questions in this area test both conceptual understanding and the ability to use correct chemical language.

Key Concepts & Formulas

Atomic number = number of protons = number of electrons (in a neutral atom)
Mass number = protons + neutrons; isotopes have the same atomic number but different mass numbers
Electron configuration: fill subshells in order 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶... (Aufbau principle)
Periodic trends: atomic radius decreases across a period (increasing nuclear charge), increases down a group
Electronegativity increases across a period and up a group; fluorine is the most electronegative element
Ionic bonding: electron transfer from metal to non-metal; electrostatic attraction between oppositely charged ions
Covalent bonding: electron sharing between non-metals; can be polar or non-polar
Bond polarity: determined by electronegativity difference — large difference = polar bond
Molecular polarity: depends on both bond polarity AND molecular geometry (VSEPR)
Metallic bonding: delocalised electrons in a lattice of positive metal ions; explains conductivity and malleability

Practice Questions

5 questions

Attempt each question before reading the hint. These are styled to match VCE exam format.

Q1.Write the electron configuration for Fe (atomic number 26) and Fe²⁺.

2 marks

Show hint

Fe²⁺ loses two electrons from the 4s subshell first.

Q2.Explain why NaCl has a high melting point but methane (CH₄) melts at very low temperatures.

3 marks

Q3.Draw the Lewis structure for SO₂ and predict its molecular geometry using VSEPR.

3 marks

Q4.Arrange in order of increasing atomic radius: Na, Mg, Al, K. Justify your answer.

3 marks

Q5.Is a molecule of CHCl₃ polar or non-polar? Explain using bond polarity and geometry.

3 marks

Common Mistakes to Avoid

These are the errors that VCE students most frequently make in Atomic Structure and Bonding — and that examiners are specifically watching for.

Writing electron configurations that violate Hund's rule — partially fill each orbital before pairing
Forgetting that transition metals lose 4s electrons first when forming ions (e.g. Fe²⁺ has configuration [Ar]3d⁶)
Concluding a molecule is polar purely because it has polar bonds — geometry must be asymmetric too
Confusing electronegativity (tendency to attract electrons in a bond) with electron affinity (energy when an isolated atom gains an electron)

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