What is a cation, and how is it formed?

A cation is a positive ion, formed when an atom loses one or more electrons.

What is an anion, and how is it formed?

An anion is a negative ion, formed when an atom gains one or more electrons.

In a dot and cross diagram, why are two different marks used for the electrons?

The dots and crosses show which atom each electron came from, even though all electrons are in fact identical.

What does a dot and cross diagram of sodium chloride show happening to the electrons?

It shows the single outer electron of sodium transferred into the outer shell of chlorine, forming Na⁺ and Cl⁻.

Why are square brackets and a charge drawn around each particle in a dot and cross diagram of an ionic compound?

They show that the particle is an ion and give the size and sign of its charge.

Edexcel GCSE Chemistry 1CH0

Key Concepts in Chemistry

Topic overview Formulae, word equations and balanced equations Hazard symbols and assessing risk The changing model of the atom Protons, neutrons and electrons The nucleus, mass number and atomic mass Elements and isotopes Calculating particle numbers and relative atomic mass Mendeleev's periodic table How the modern periodic table is arranged Electronic configuration and the periodic table How ionic bonds form Ions in ionic compounds Formulae of ionic compounds Naming compounds and the ionic lattice Covalent bonds and molecules Dot and cross diagrams for simple molecules Classifying substances and the properties of ionic compounds Properties of simple molecular substances, and forms of carbon Graphite and diamond Fullerenes and graphene Polymers and models of bonding The properties of metals Relative formula mass and percentage composition Empirical and molecular formulae Conservation of mass in closed and open systems Reacting masses from balanced equations Concentration in grams per cubic decimetre

States of Matter and Mixtures

Topic overview The three states of matter and changes of state Energy changes during changes of state, and predicting state Pure substances and melting point data Choosing a separation technique Separating a mixture in practice Paper chromatography and interpreting a chromatogram Investigating inks by distillation and chromatography Making water potable

Chemical Changes

Topic overview Acids, alkalis and the pH scale Indicators: litmus, methyl orange and phenolphthalein Investigating pH change when neutralising an acid Bases and alkalis Reactions of acids, and testing for hydrogen and carbon dioxide Neutralisation and its ionic equation Preparing soluble salts from insoluble and soluble reactants Preparing pure, dry copper sulfate crystals Carrying out an acid-alkali titration Solubility rules Predicting precipitates and preparing an insoluble salt Electrolytes and what electrolysis is Movement of ions and predicting the products of molten electrolysis Electrolysis with inert electrodes Electrolysis of copper sulfate solution Investigating the electrolysis of copper sulfate

Extracting Metals and Equilibria

Topic overview Investigating the reactivity of metals The reactivity series Ores, oxidation and reduction Choosing a method to extract a metal Corrosion resistance and recycling metals Life cycle assessment Reversible reactions and dynamic equilibrium The Haber process and its conditions

Transition Metals, Quantitative Chemistry and Industrial Processes

Topic overview Transition metals and their properties Corrosion and electroplating Preventing rusting Alloys and alloy steels How the uses of metals relate to their properties Carrying out an accurate titration Percentage yield Atom economy The Haber process Fertilisers and ammonium salts Preparing ammonium sulfate in the lab and in industry Chemical cells and fuel cells Evaluating fuel cells

Groups in the Periodic Table

Topic overview The groups of the periodic table, and the alkali metals Reactions of the alkali metals with water The pattern in alkali metal reactivity and why it happens Physical properties of the halogens The test for chlorine, and halogens reacting with metals Hydrogen halides, and explaining halogen reactivity Displacement reactions of the halogens Group 0: the noble gases

Rates of Reaction and Energy Changes

Topic overview Investigating the rate of a reaction Measuring rate and interpreting rate graphs Collision theory and factors affecting rate Catalysts and enzymes Exothermic and endothermic changes Bond breaking, bond making and the overall energy change Activation energy and reaction profiles

Fuels and Earth Science

Topic overview Hydrocarbons and crude oil Fractional distillation and the fractions Properties of the fractions and homologous series Complete and incomplete combustion Carbon monoxide and soot Pollutants and acid rain Hydrogen and fossil fuels compared Cracking and why it is necessary The Earth's early atmosphere How the oceans formed and how oxygen appeared The test for oxygen and the greenhouse gases Today's atmosphere and evidence for climate change

Chemical Analysis, Organic Chemistry and Materials

Key Concepts in Chemistry

How ionic bonds form

2 things to know
Papers 1 and 2

Overview

Electron transfer between a metal and a non-metal, cations and anions, what dot and cross diagrams show, what an ion is and why a chloride ion is negative.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Explain how an ionic bond forms and how the two kinds of ion involved are made.

Process

How is an ionic bond formed?

Questions from this subtopic

Each one with the model answer underneath.

1
How is an ionic bond formed?
Model answer
Electrons are transferred from a metal atom to a non-metal atom, and the oppositely charged ions produced attract one another.
2
What is a cation, and how is it formed?
Model answer
A cation is a positive ion, formed when an atom loses one or more electrons.
3
What is an anion, and how is it formed?
Model answer
An anion is a negative ion, formed when an atom gains one or more electrons.
4
In a dot and cross diagram, why are two different marks used for the electrons?
Model answer
The dots and crosses show which atom each electron came from, even though all electrons are in fact identical.
5
What does a dot and cross diagram of sodium chloride show happening to the electrons?
Model answer
It shows the single outer electron of sodium transferred into the outer shell of chlorine, forming Na⁺ and Cl⁻.
6
Why are square brackets and a charge drawn around each particle in a dot and cross diagram of an ionic compound?
Model answer
They show that the particle is an ion and give the size and sign of its charge.

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Key Concepts in Chemistry

States of Matter and Mixtures

Chemical Changes

Extracting Metals and Equilibria

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A holds the acid.

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AChlorine is a pale green gas at room temperature.

BBromine is a red-brown liquid at room temperature.

CIodine is a dark grey solid at room temperature.

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An atom is about 0.1 nm across.

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