Edexcel A Level Chemistry Topic 1: Atomic Structure and the Periodic Table Exam Questions

About Edexcel A Level Chemistry Topic 1: Atomic Structure and the Periodic Table

Topic 1 of Edexcel A Level Chemistry builds the model of the atom used throughout the course. You need to describe protons, neutrons and electrons, use mass spectra to calculate relative atomic mass and find relative molecular mass, and write electronic configurations using s, p and d orbitals. Successive and first ionisation energies are used as evidence for shells and subshells, and the topic finishes with periodicity: trends in atomic radius, ionisation energy and melting temperature across Periods 2 and 3. It is assessed in Paper 1 (Advanced Inorganic and Physical Chemistry) and Paper 3. Examiners commonly test ionisation energy explanations, mass spectrum calculations and configurations of ions.

What you need to know

• Atoms and isotopes Isotopes have the same number of protons but different numbers of neutrons. Relative atomic mass is the weighted mean mass of an atom of an element relative to 1/12 of the mass of an atom of carbon-12.
• Mass spectrometry A mass spectrum shows m/z against abundance. Calculate Ar from isotope masses and abundances, and use the molecular ion peak to find the relative molecular mass of a compound.
• Orbitals and configurations s orbitals are spherical and p orbitals dumbbell shaped, each holding two electrons of opposite spin. Configurations for elements up to Z = 36 follow 1s 2s 2p 3s 3p 4s 3d 4p, with Cr and Cu as exceptions.
• Ionisation energy First ionisation energy is the energy needed to remove one electron from each atom in one mole of gaseous atoms. It is affected by nuclear charge, distance from the nucleus and shielding.
• Evidence for shells and subshells Large jumps in successive ionisation energies show a new inner shell. Dips in first ionisation energy at Group 3 (electron in p subshell) and Group 6 (paired p electrons repel) show subshells.
• Periodicity Elements are classified as s, p or d block. Across Period 3, melting temperature rises to silicon (giant covalent) then falls for simple molecular elements, and atomic radius decreases as nuclear charge increases.

Common mistakes in Topic 1: Atomic Structure and the Periodic Table

• Missing (g) state symbols in ionisation energy equations.
• Calculating Ar without dividing by the total abundance when abundances do not add up to 100.
• Writing Cu as [Ar]3d9 4s2; the correct configuration is [Ar]3d10 4s1.
• Explaining the Group 6 dip using distance from the nucleus instead of repulsion between paired electrons in the same p orbital.
• Saying shielding increases across a period; electrons are added to the same shell so shielding stays roughly constant.

Try three Topic 1: Atomic Structure and the Periodic Table exam-style questions