The Structure of the Atom
Build confidence in The Structure of the Atom for GCSE Chemistry with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Atoms have a tiny central nucleus of protons and neutrons surrounded by electrons in shells, with a radius of about 1 × 10⁻¹⁰ m.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
Atoms have a radius of about 0.1 nanometres, which is 1 × 10⁻¹⁰ metres. The nucleus is far smaller, with a radius of less than 1/10000 of that of the atom.
The nucleus contains protons and neutrons and holds almost all of the atom's mass. Electrons are arranged in energy levels, or shells, around the nucleus at different distances.
Protons have a relative charge of +1 and a relative mass of 1. Neutrons have no charge and a relative mass of 1. Electrons have a relative charge of −1 and a negligible mass. Because atoms have equal numbers of protons and electrons, they have no overall charge.
Revision notes
Size and structure
An atom has a radius of about 0.1 nm, or 1 × 10⁻¹⁰ m.
The nucleus is less than 1/10000 of the radius of the atom, but contains almost all of its mass. Electrons occupy energy levels at different distances from the nucleus.
The subatomic particles
Proton: relative charge +1, relative mass 1, found in the nucleus.
Neutron: relative charge 0, relative mass 1, found in the nucleus. Electron: relative charge −1, negligible mass, in shells around the nucleus.
Why atoms are neutral
The number of protons in an atom equals the number of electrons.
Because the +1 charge of each proton is balanced by the −1 charge of each electron, atoms have no overall electrical charge.
Key points
- An atom has a radius of about 0.1 nm.
- The nucleus is less than 1/10000 of the atom's radius.
- The nucleus contains protons and neutrons.
- Almost all the mass is in the nucleus.
- Electrons occupy energy levels around the nucleus.
- Atoms are neutral because protons equal electrons.
Worked examples
Example 1
Give the relative charge and relative mass of a proton, a neutron and an electron. [3 marks]
Model answer
Proton: charge +1, mass 1 (1 mark). Neutron: charge 0, mass 1 (1 mark). Electron: charge −1, negligible mass (1 mark).
Example 2
Explain why an atom has no overall electrical charge. [2 marks]
Model answer
An atom contains equal numbers of protons and electrons (1 mark), and the positive charge of each proton is balanced by the negative charge of each electron (1 mark).
Example 3
Explain why almost all the mass of an atom is in its nucleus. [2 marks]
Model answer
The nucleus contains the protons and neutrons, which each have a relative mass of 1 (1 mark), whereas the mass of an electron is negligible in comparison (1 mark).
Common mistakes
Saying electrons have a mass of 1.
Their mass is negligible compared with protons and neutrons.
Giving the nucleus a negative charge.
It is positive, because it contains protons and neutrons only.
Confusing the size of the atom and the nucleus.
The nucleus is less than 1/10000 of the atom's radius.
Saying atoms are neutral because they have no charged particles.
They do have charged particles; the charges balance exactly.
Exam tips
- Learn the three particles as a table of charge and mass.
- Explain neutrality through balanced numbers of protons and electrons.
- Give the atomic radius in standard form when asked.
- Say negligible rather than zero for electron mass.
Key terms
- Nucleus
- The central part of an atom containing protons and neutrons.
- Proton
- A positively charged particle in the nucleus.
- Neutron
- An uncharged particle in the nucleus.
- Energy level
- A shell in which electrons are arranged around the nucleus.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.