Definitions - Topic 1 - Atomic Structure and the Periodic Table - AQA Chemistry GCSE

Sep 5, 2026

A study-focused set of AQA Chemistry GCSE Topic 1 definitions covering atomic structure and the periodic table. Key terms explain core particle ideas (atom, nucleus, proton, neutron, electron, ion, isotope, mass number), energy-level concepts (electron shells), and model-based interpretations (nuclear model, plum pudding model). It also defines chemical substance categories (elements, metals, non-metals, noble gases, halogens, alkali metals, transition metals) and common separation methods (chromatography, filtration, crystallisation, fractional distillation, simple distillation) alongside mixture and compound classifications.

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Topic 1: Atomic Structure and the Periodic Table - Definitions

Atomic particles and atomic models

Elements, groups, and ions

Separation techniques and mixtures

Definitions and Concepts for AQA Chemistry GCSE Topic 1-Atomic Structure and the Periodic Table Definitions in bold are for higher tier only Definitions marked by‘*’are for separate sciences only Definitions have been taken, or modified from the AQA Specification for GCSE Chemistry, 8462, Version 1.1 04 October 2019. Alkali metals: The elements in Group 1 of the periodic table. Atom: The smallest part of an element that can exist. All substances are made up of atoms. Atomic nucleus: Positively charged object composed of protons and neutrons at the centre of every atom with one or more electrons orbiting it. Atomic number: The number of protons in the nucleus. Chromatography: A separation technique used to separate a mixture of chemicals by distributing the components between two phases. Compound: A substance made up of two or more types of atoms chemically combined together. Crystallisation: A separation technique used to produce solid crystals from a solution by evaporating the solvent. Displacement: A chemical reaction in which a more reactive element displaces a less reactive element from its compound. Electron: Negatively charged subatomic particle which orbit the nucleus at various energy levels. Very small relative mass (negligible) . Electron shell: Different energy levels in atoms occupied by electrons. Element: A substance made up of only one type of atom. Filtration: A separation technique used to separate solids from liquids. Fractional distillation: A method of separating a mixture of substances according to their different boiling points. Group (periodic table): The columns of the periodic table represent different groups of elements. Elements with similar properties are in the same group. Halogens: The elements in Group 7 of the periodic table. Ion: An atom or molecule with an electric charge due to the loss or gain of electrons. Isotope: Atoms of the same element with the same number of protons but a different number of neutrons. Mass number: The total number of protons and neutrons in the nucleus. Metals: Elements that react to form positive ions. Found to the left and towards the bottom of the periodic table. Mixture: A mixture consists of two or more elements or compounds not chemically combined together. Neutron: Neutral subatomic particle present in the nucleus of the atom. Relative mass of 1. Noble gases: The elements in Group 0 of the periodic table. Non-metals: Elements that react to form negative ions. Found towards the right and top of the periodic table. Nuclear model: The nuclear atomic model stated that the mass was concentrated at the centre of the atom and that the nucleus was charged. Periodic table: Table of elements arranged in order of atomic number and such that elements with similar properties are in the same column (group) . Plum pudding model: Atomic model devised after the discovery of the electron. The model suggests the atom is a ball of positive charge with negative electrons scattered through it. Proton: Positively charged subatomic particle present in the nucleus of the atom. Relative mass of 1. Relative atomic mass: An average value that takes account of the abundance of the isotopes of the element. Simple distillation: A procedure by which two liquids with different boiling points can be separated. Transition metals: The collection of metallic elements in the middle of the periodic table.

FAQs

What is the difference between an atom, an ion, and an isotope?

An atom is the smallest part of an element that can exist. An ion has an electric charge due to loss or gain of electrons. An isotope is an atom of the same element with the same number of protons but a different number of neutrons.

How do the atomic nucleus, atomic number, and mass number relate?

The atomic nucleus is positively charged and composed of protons and neutrons. The atomic number equals the number of protons. The mass number is the total number of protons and neutrons.

Which separation methods are defined for mixtures and solutions?

Chromatography separates components using two phases. Filtration separates solids from liquids. Crystallisation produces solid crystals from a solution by evaporating the solvent. Fractional distillation separates substances by different boiling points, and simple distillation separates two liquids with different boiling points.

Sep 5, 2026

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