AQA GCSE Chemistry 8462: Atomic Structure and the Periodic Table Notes

Page 1: AQA Scheme of Work Overview and Course Administration

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This document outlines the Scheme of Work for Chemistry – Atomic structure and the periodic table, specifically for the new GCSE Chemistry (8462). The resource has been updated from draft versions to reflect the accredited specification, including learning outcomes and opportunities for developing practical and enquiry skills. It is designed as a flexible medium-term plan for teaching curriculum content and skills assessed in the qualification. It is not exhaustive and suggests optional activities and resources.

Page 2: 4.1.1.1 Atoms, Elements, and Compounds

Specification Reference 4.1.1.1

Key Concepts and Definitions

Atoms: All substances are composed of atoms. An atom is defined as the smallest part of an element that can exist.
Elements: There are approximately $100$ different elements, all of which are displayed in the Periodic Table. Each element is represented by a specific chemical symbol (e.g., ‘O’ represents an atom of oxygen).
Compounds: Formed from elements through chemical reactions. They contain two or more elements chemically combined in fixed proportions. Compounds can be represented by formulae using the symbols of the constituent atoms.
Chemical Reactions: These processes always involve the formation of one or more new substances and frequently involve a detectable change in energy.

Learning Outcomes and Skills

Use names and symbols for the first $20$ elements, Group $1$ , Group $7$ , and other specified elements.
Name compounds from formulae or symbol equations.
Write word equations for reactions.
Develop symbolic communication skills to write balanced symbol equations.

Suggested Activities

Model atoms using physical models or computer simulations.
Research history of element names and symbols.
Practical: Burning magnesium or sodium in oxygen.
Resources: BBC Bitesize (Structure of an atom), Royal Society of Chemistry interactive Periodic Table.

Page 3: 4.1.1.1 (Continued) and 4.1.1.2 Mixtures

Chemical Equations (HT Only) In addition to word and balanced chemical equations, Higher Tier students should be able to write balanced half equations and ionic equations where appropriate.

Specification Reference 4.1.1.2: Mixtures

Definitions and Properties

Mixture: Consists of two or more elements or compounds not chemically combined. The chemical properties of each individual substance in a mixture remain unchanged.
Separation: Mixtures are separated by physical processes. These do not involve chemical reactions, and no new substances are created.

Physical Separation Techniques

Filtration: Separating insoluble solids from liquids.
Crystallisation: Obtaining a soluble solid from a solution (Explain why this occurs).
Simple Distillation: Separating a solvent from a solution.
Fractional Distillation: Separating a mixture of liquids with different boiling points.
Chromatography: Separating substances based on their solubility in a solvent.

Practical Applications

Chromatography using felt-tip pens or sweets.
Distillation of citrus peel.
Crystallisation using salol.
Filtration and evaporation of sea water.
Analysis of mineral waters to show they are not ‘pure’ in scientific terms.

Page 4: 4.1.1.3 The History of the Atomic Model

Evolution of Scientific Models New experimental evidence leads to the revision or replacement of scientific models.

Chronological Development

Pre-electron: Atoms were thought to be indivisible, tiny spheres.
Discovery of the Electron: Led to the Plum-Pudding Model, which described the atom as a ball of positive charge with negative electrons embedded throughout.
Alpha Particle Scattering Experiment: The results led to the replacement of the plum-pudding model with the Nuclear Model.
Niels Bohr Adaptation: Suggested that electrons orbit the nucleus at specific distances. Theoretical calculations for this model aligned with experimental observations.

Learning Outcomes

Describe how and why the atomic model changed over time.
Differentiate between the plum-pudding and nuclear models.
Explain why scattering experiment evidence necessitated change.

Page 5: 4.1.1.3 (Continued) Protons and Neutrons

Discovery of Internal Structure

Protons: Later experiments showed the positive charge of a nucleus could be divided into smaller particles, each possessing the same amount of positive charge. These were named protons.
Neutrons: The experimental work of James Chadwick provided evidence for the existence of neutrons within the nucleus, approximately $20$ years after the nuclear model was established.

Page 6: 4.1.1.4 and 4.1.1.5 Charges and Sizes of Atoms

Specification Reference 4.1.1.4: Relative Electrical Charges

Subatomic Particles and Their Charges

Proton: $+1$
Neutron: $0$
Electron: $-1$

Key Principles

Atomic Neutrality: Atoms have no overall electrical charge because the number of electrons equals the number of protons.
Atomic Number: The number of protons in an atom. All atoms of a given element have the same number of protons. Different elements have different atomic numbers.

Specification Reference 4.1.1.5: Atomic Size and Nuclear Scale

Dimensions

Atomic Radius: Approximately $0.1\,nm$ ( $1 \times 10^{-10}\,m$ ).
Nuclear Radius: Less than $\frac{1}{10\,000}$ of the atomic radius (approximately $1 \times 10^{-14}\,m$ ).

Page 7: 4.1.1.5 (Continued) Mass and Isotopes

Atomic Mass Distribution Standard atomic mass is concentrated almost entirely in the nucleus.

Relative Masses

Proton: $1$
Neutron: $1$
Electron: Very small (negligible).

Definitions

Mass Number: The total sum of protons and neutrons in an atom.
Isotopes: Atoms of the same element with the same number of protons but different numbers of neutrons.

Atomic Representation Example $^{23}_{11}Na$

Mass Num ( $23$ ): Sum of protons and neutrons.
Atomic Num ( $11$ ): Number of protons.

Page 8: 4.1.1.6 Relative Atomic Mass and 4.1.1.7 Electronic Structure

Specification Reference 4.1.1.6: Relative Atomic Mass ( $A_r$ ) $A_r$ is an average value that accounts for the abundance of the isotopes of an element.

Specification Reference 4.1.1.7: Electronic Structure

Arrangement Rules

Electrons occupy the lowest available energy levels (innermost shells) first.
Maximum capacities: $2$ in the first shell, $8$ in the second, and $8$ in the third (for the first $20$ elements).
Representation: Can be shown as numbers (e.g., sodium as $2, 8, 1$ ) or as dot-and-cross diagrams.

Page 9: 4.1.2 The Periodic Table

Specification Reference 4.1.2.1: Arrangement

Elements are arranged by atomic (proton) number.
Elements with similar properties are placed in vertical columns called Groups.
The table is ‘periodic’ because similar properties recur at regular intervals.
Elements in the same group share the same number of electrons in their outer shell, resulting in similar chemical properties.

Page 10: 4.1.2.2 History of the Periodic Table

Evolution of Classification

Early Tables: Scientists initially arranged elements by atomic weight. These were incomplete and often placed elements in groups with dissimilar properties.
Mendeleev’s Contribution: He overcame earlier issues by leaving gaps for undiscovered elements. He occasionally swapped the order of elements (deviating from strict atomic weight) to ensure elements with similar properties stayed together.
Validation: Discovery of elements that matched Mendeleev’s predictions supported his model. Knowledge of isotopes eventually explained why atomic weight orders were not always accurate.

Page 11: 4.1.2.3 and 4.1.2.4 Metals, Non-metals, and Group 0

Specification Reference 4.1.2.3: Metals and Non-metals

Metals: Elements that react to form positive ions. Most elements are metals, located on the left and bottom of the table.
Non-metals: Elements that do not form positive ions. Located on the top and right of the table.

Specification Reference 4.1.2.4: Group 0 (Noble Gases)

Properties: Unreactive (inert) elements that do not easily form molecules.
Electronic Structure: Stable arrangement with $8$ electrons in the outer shell (except Helium, which has $2$ ).
Boiling Point Trend: Boiling points increase as you go down the group (with increasing relative atomic mass).

Page 12: 4.1.2.4 (Continued) and 4.1.2.5 Group 1 (Alkali Metals)

Group 0 Summary Properties depend on the stable outer shell configuration.

Specification Reference 4.1.2.5: Group 1

Properties: Known as Alkali Metals. They possess a single electron in the outer shell.
Reactions: React with oxygen, chlorine, and water.
Reactivity Trend: Reactivity increases as you go down the group.

Page 13: 4.1.2.6 Group 7 (Halogens)

Group 7 Characteristics

Structure: Non-metals consisting of molecules made of pairs of atoms ( $X_2$ ).
Trends Down the Group:
- Increase in relative molecular mass.
- Increase in melting point and boiling point.
- Decrease in reactivity.
Displacement Reactions: A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt (e.g., using $KCl$ , $KBr$ , or $KI$ ).

Page 15: 4.1.3 Properties of the Transition Metals

Specification Reference 4.1.3.1: Comparison with Group 1 Transition elements are metals with properties that differ significantly from Group $1$ alkali metals.

Physical Differences:

Higher melting points.
Higher densities.
Greater strength and hardness.

Chemical Differences:

Lower reactivity with oxygen, water, and halogens.
Exemplar elements: Chromium ( $Cr$ ), Manganese ( $Mn$ ), Iron ( $Fe$ ), Cobalt ( $Co$ ), Nickel ( $Ni$ ), and Copper ( $Cu$ ).

Specification Reference 4.1.3.2: Secondary Properties

Ions: Transition metals often form ions with different charges.
Appearance: They form coloured compounds.
Utility: They are frequently used as catalysts.

Core Mathematical Skills for Topic 4.1

1b: Recognizing and using expressions in standard form.
5b: Visualizing and representing $2D$ and $3D$ forms, including the two-dimensional representation of $3D$ objects.