How is the number of neutrons in an atom worked out?

By subtracting the atomic number from the mass number.

Atoms of the same element that have the same number of protons but different numbers of neutrons.

A particle with an overall electrical charge, formed when an atom or group of atoms loses or gains electrons.

In the standard notation for an atom, where are the mass number and the atomic number written?

Both are written to the left of the element symbol, with the mass number above and the atomic number below.

OCR GCSE Combined Science Chemistry J250

Chemical Reactions

Topic overview Writing formulae of elements and compounds Balanced equations, and deducing formulae from ions Ionic equations, and state symbols The mole and the Avogadro constant Conservation of mass, and changes of mass in open systems Stoichiometry, and calculating reacting masses Exothermic and endothermic reactions, and reaction profiles Activation energy, and bond energy calculations Oxidation and reduction, by oxygen and by electrons Acids, alkalis and neutralisation The ionic equation for neutralisation, and reactions of acids Dilute and concentrated, weak and strong The pH scale, and hydrogen ion concentration pH as a factor of ten, and measuring pH Products at the electrodes, and molten ionic compounds Electrolysis of aqueous solutions Inert and non-inert electrodes

Elements, Compounds and Mixtures

Topic overview Purity, and melting point data Relative formula mass and empirical formulae Formulations, and separating mixtures Paper and thin layer chromatography Interpreting chromatograms and Rf values Choosing a purification method Metals and non-metals in the Periodic Table Electron arrangement and position in the Periodic Table Ionic, covalent and metallic bonding compared Dot and cross diagrams, and the limits of models Reactions, electron arrangement and Mendeleev's table Carbon's four bonds, and the variety of organic compounds Diamond, graphite, fullerenes and graphene Bond strength, intermolecular forces and predicting state Bulk properties of ionic, molecular and giant structures

Global Challenges

Topic overview Extracting metals by reduction and by electrolysis Biological methods of metal extraction Life cycle assessment Recycling, and the decisions behind it Fractional distillation of crude oil The fractions, and crude oil as a feedstock Dependence on hydrocarbons, and cracking The Earth's early atmosphere, and how oxygen developed The greenhouse effect, and evidence for climate change Effects of carbon dioxide and methane, and air pollutants Producing potable water

Monitoring and Controlling Chemical Reactions

Topic overview Mass of solute, concentration and dilution calculations Measuring the rate of a reaction, and rate graphs Factors affecting rate, and collision theory Surface area and rate Catalysts and how they work Reversible reactions and dynamic equilibrium Changing the conditions of an equilibrium Activation energy, and enzymes as catalysts

Particles

Topic overview The particle model and changes of state Limitations of the particle model How the atomic model changed, and the structure of the atom The size of atoms, and the subatomic particles Calculating protons, neutrons and electrons

Predicting and Identifying Reactions

Topic overview Groups 1, 7 and 0, and why they behave as they do Predicting reactivity from the Periodic Table Reactivity of metals with water and acids Tests for oxygen, hydrogen, carbon dioxide and chlorine

Particles

Calculating protons, neutrons and electrons

3 things to know
Paper 9 (Chemistry)

Overview

What atomic number and mass number are, working out the number of neutrons, what isotopes and ions are, where the two numbers are written beside a symbol, and counting the protons, neutrons and electrons in an atom and in chloride and magnesium ions.

What you need to know

Answer each one before you reveal it.

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Key term

What is the atomic number of an element?

Key term

What is the mass number of an atom?

Key term

What are isotopes?

Questions from this subtopic

Each one with the model answer underneath.

1
What is the atomic number of an element?
Model answer
The number of protons in the nucleus of one of its atoms.
2
What is the mass number of an atom?
Model answer
The total number of protons and neutrons in its nucleus.
3
How is the number of neutrons in an atom worked out?
Model answer
By subtracting the atomic number from the mass number.
4
What are isotopes?
Model answer
Atoms of the same element that have the same number of protons but different numbers of neutrons.
5
What is an ion?
Model answer
A particle with an overall electrical charge, formed when an atom or group of atoms loses or gains electrons.
6
In the standard notation for an atom, where are the mass number and the atomic number written?
Model answer
Both are written to the left of the element symbol, with the mass number above and the atomic number below.

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Chemical Reactions

Elements, Compounds and Mixtures

Global Challenges

Monitoring and Controlling Chemical Reactions

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AMetals are on the left and in the centre, and non-metals are on the right-hand side.

BKI, because potassium loses one electron and iodine gains one.

CCaCl₂, because a calcium atom loses two electrons and each chlorine atom gains one.

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Sodium ions give a bright yellow flame colour.

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Calculating protons, neutrons and electrons

Overview

What you need to know

What is the atomic number of an element?

What is the mass number of an atom?

What are isotopes?

Questions from this subtopic

What is the atomic number of an element?

What is the mass number of an atom?

How is the number of neutrons in an atom worked out?

What are isotopes?

What is an ion?

In the standard notation for an atom, where are the mass number and the atomic number written?

Other ways to work this

What is inside Levo

See a huge jump in your memorisation

Cram a whole paper in one sitting

Blank Blitz consolidates the facts

Build It trains answer structure

Test It catches misconceptions

Brain Breaks between sessions

Every question in Particles, on a schedule.