AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Relative electrical charges of subatomic particles: Students should be able to use the nuclear model to describe atoms.
The nuclear model describes an atom as a small, dense, positively charged nucleus surrounded by electrons in shells or energy levels.
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
The nuclear model describes an atom as a small, dense, positively charged nucleus surrounded by electrons in shells or energy levels. The nucleus contains protons, which are positively charged, and neutrons, which are neutral. Almost all the mass of an atom is in the nucleus, but the nucleus occupies only a tiny fraction of the atom's volume. Electrons are negatively charged and occupy most of the atom's volume. In a neutral atom, the number of electrons equals the number of protons, so the total negative charge balances the total positive charge. The model explains why atoms are neutral overall and why most of an atom is empty space.
What earns the marks
- Describe the atom as having a small, dense, positively charged nucleus at its centre.
- State that the nucleus contains protons and neutrons, with protons positive and neutrons neutral.
- State that electrons are negatively charged and occupy shells or energy levels around the nucleus.
- Explain that in a neutral atom the number of electrons equals the number of protons, so the charges balance.
- Explain that most of the atom's mass is in the nucleus but most of its volume is the space occupied by electrons.
Common mistakes and how to put them right
Saying that electrons orbit the nucleus like planets orbit the Sun in fixed paths.
Put it right: Electrons occupy shells or energy levels, and their exact positions are not fixed paths.
Thinking that the nucleus is large compared with the whole atom.
Put it right: The nucleus is very small and dense, while electrons occupy most of the atom's volume.
Stating that neutrons are positively charged.
Put it right: Neutrons are neutral, protons are positive and electrons are negative.
Exam tips
- Use the words nucleus, protons, neutrons, electrons and shells when describing the nuclear model.
- When explaining why an atom is neutral, refer to equal numbers of protons and electrons rather than saying the charges cancel without explanation.
- If asked to compare the nuclear model with an earlier model, focus on the presence of a central nucleus and the arrangement of electrons.
Try the lesson
The start of the Relative electrical charges of subatomic particles: Students should be able to use the nuclear model to describe atoms. lesson, made from checked teaching notes for this specification point.
Have a go first
In the nuclear model of the atom, which part of the atom contains the protons and neutrons?
Listen
The nuclear model describes an atom as a small, dense, positively charged nucleus surrounded by electrons in shells or energy levels. The nucleus contains protons, which are positively charged, and neutrons, which are neutral. Almost all the mass of an atom is in the nucleus, but the nucleus occupies only a tiny fraction of the atom's volume. Electrons are negatively charged and occupy most of the atom's volume. In a neutral atom, the number of electrons equals the number of protons, so the total negative charge balances the total positive charge. The model explains why atoms are neutral overall and why most of an atom is empty space. A strong answer earns marks for these points. Describe the atom as having a small, dense, positively charged nucleus at its centre. State that the nucleus contains protons and neutrons, with protons positive and neutrons neutral. State that electrons are negatively charged and occupy shells or energy levels around the nucleus. Explain that in a neutral atom the number of electrons equals the number of protons, so the charges balance. A common slip: Saying that electrons orbit the nucleus like planets orbit the Sun in fixed paths. Instead, electrons occupy shells or energy levels, and their exact positions are not fixed paths. Exam tip: Use the words nucleus, protons, neutrons, electrons and shells when describing the nuclear model.
Key words
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Nuclear model of the atom
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Subatomic particle charges
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Mass and volume distribution in atoms
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Neutrality of atoms
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See every definition
- Nuclear model of the atom
- Describes an atom as a small, dense, positively charged nucleus surrounded by electrons in shells or energy levels.
- Subatomic particle charges
- Protons are positively charged, neutrons are neutral and electrons are negatively charged.
- Mass and volume distribution in atoms
- Almost all the mass of an atom is in the nucleus, but the nucleus occupies only a tiny fraction of the atom's volume, while electrons occupy most of the volume.
- Neutrality of atoms
- In a neutral atom, the number of electrons equals the number of protons, so the total negative charge balances the total positive charge.
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