Relative electrical charges of subatomic particles — AQA GCSE Combined Science
Test yourself on Relative electrical charges of subatomic particles with AQA GCSE practice questions.
7 days Premium · Then free forever · No card, no charge
Relative electrical charges of subatomic particles explained
Atoms contain three subatomic particles whose electrical charges are compared using relative values rather than coulombs.
Read the full explanation
A proton carries a relative charge of 1⁺, an electron carries a relative charge of 1⁻, and a neutron carries no charge, written as 0. These values are relative because they compare each particle's charge with the magnitude of a proton's charge, so the numbers stay simple. For example, a nucleus containing 11 protons has a total positive charge of 11⁺, while 11 electrons surrounding it give a total negative charge of 11⁻. Because the charges are equal in magnitude and opposite in sign, they cancel. Knowing these relative charges lets you work out the overall charge of any atom or ion from its particle counts, and it underpins later work on ionic bonding and electrolysis.
In an atom, the number of electrons is equal to the number of protons in the nucleus. Atoms have no overall electrical charge.
Every atom of an element has a fixed number of protons in its nucleus, called the atomic number, and a neutral atom has exactly the same number of electrons arranged around the nucleus. Because each proton has a relative charge of 1⁺ and each electron has a relative charge of 1⁻, equal numbers of the two particles produce equal but opposite total charges. These cancel completely, so the atom has no overall electrical charge. For example, a carbon atom has 6 protons and therefore 6 electrons: the total positive charge is 6⁺ and the total negative charge is 6⁻, giving an overall charge of 0. If the numbers become unequal, as happens when electrons are gained or lost, the particle becomes a charged ion instead.
The number of protons in an atom of an element is its atomic number. All atoms of a particular element have the same number of protons. Atoms of different elements have different numbers of protons.
The atomic number (proton number) is the defining property of an element. It equals the number of protons in the nucleus of one atom. Every atom of a given element has the same proton count, so the atomic number is constant for that element. Atoms of different elements have different proton counts, so their atomic numbers differ. For example, every hydrogen atom has 1 proton, so its atomic number is 1; every carbon atom has 6 protons, so its atomic number is 6. In a neutral atom, the number of electrons equals the number of protons, so atomic number also tells you the electron count. The proton count never changes in chemical reactions; it only changes in nuclear processes.
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. 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.
Your focus
- Recall the relative electrical charge of a proton, a neutron and an electron.
- Explain why the charges are described as relative rather than absolute.
- Determine the overall electrical charge of a particle from its numbers of protons and electrons.
Show all 12 objectives
- Describe the relationship between the number of protons and the number of electrons in an atom.
- Explain why an atom has no overall electrical charge.
- Deduce the number of electrons in a neutral atom from its atomic number.
- Define atomic number as the number of protons in an atom.
- Explain why all atoms of an element have the same atomic number and why different elements have different atomic numbers.
- Use atomic number to identify an element and to deduce the number of electrons in a neutral atom.
- Describe the structure of an atom using the nuclear model, including the nucleus, protons, neutrons and electrons.
- Explain how the charges of protons, neutrons and electrons account for the overall neutrality of an atom.
- Compare the mass and volume distribution of the nucleus and the electron shells in an atom.
Relative electrical charges of subatomic particles exam tips
Marking Points
- State that a proton has a relative electrical charge of 1⁺.
- State that an electron has a relative electrical charge of 1⁻.
- State that a neutron has a relative electrical charge of 0, meaning it is neutral.
- Explain that the values are relative to the magnitude of the charge on a proton, so they are not measured in coulombs.
- Use the relative charges to calculate the overall charge of a particle from its numbers of protons and electrons, for example 12 protons and 10 electrons gives an overall charge of 2⁺.
- State that in an atom the number of electrons equals the number of protons.
- Link the equal numbers to the equal magnitudes of the proton and electron charges, 1⁺ and 1⁻.
- Explain that the positive and negative charges cancel, so the overall charge of an atom is zero.
- Use the atomic number to deduce the number of electrons in a neutral atom, for example atomic number 17 means 17 electrons.
- Recognise that unequal numbers of protons and electrons produce an ion with an overall charge, such as 11 protons with 10 electrons giving 1⁺.
- State that the atomic number is the number of protons in an atom.
- Explain that all atoms of the same element have the same number of protons, so the atomic number is fixed for that element.
- Explain that atoms of different elements have different numbers of protons, so their atomic numbers are different.
- Use a specific element as an example, such as hydrogen with 1 proton or carbon with 6 protons, to show the link between proton number and atomic number.
- Recognise that in a neutral atom the number of electrons equals the number of protons, so atomic number also gives the electron count.
- 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.
Examiner Tips
- 💡Learn the three values as a matched set: proton 1⁺, neutron 0, electron 1⁻.
- 💡When a question gives particle numbers, subtract the number of electrons from the number of protons to find the overall charge.
- 💡Check the sign as well as the size of any charge you write, because a missing or reversed sign loses the mark even when the number is right.
- 💡Use the atomic number as the starting point: it gives the proton count, and for an atom the electron count is the same.
- 💡Show the cancellation explicitly, for example 8⁺ and 8⁻ give an overall charge of 0, to make your reasoning clear.
- 💡If a question asks why an atom is neutral, refer to equal numbers of protons and electrons rather than simply stating that it has no charge.
- 💡Read the question carefully to check whether it asks for the atomic number, the mass number or the number of neutrons, and use the correct definition.
- 💡When given a symbol such as ¹²C or ¹⁶O, use the lower number as the atomic number and the upper number as the mass number.
- 💡Link the proton count to the element identity in your answer, for example by stating that 6 protons means the atom is carbon.
- 💡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.
Common Mistakes
- Writing the neutron's charge as 1⁰ or leaving it blank: the correct value is 0, because a neutron is electrically neutral.
- Giving the electron a positive charge: the electron is negative, so its relative charge is 1⁻, while the proton is 1⁺.
- Treating the relative charge values as coulomb measurements: they are comparisons with the proton's charge magnitude, so no unit is attached.
- Assuming the number of neutrons must also equal the number of protons: neutrons vary between isotopes and do not affect the overall charge.
- Saying atoms have no charged particles at all: atoms contain charged protons and electrons, but their charges cancel.
- Forgetting that the rule applies to atoms only, so a particle with unequal proton and electron counts is an ion and does carry an overall charge.
- Confusing atomic number with mass number. Correction: atomic number counts protons only, while mass number counts protons plus neutrons.
- Thinking that atoms of the same element can have different numbers of protons. Correction: all atoms of an element have the same proton count; differing neutron numbers produce isotopes, not different elements.
- Assuming the atomic number equals the number of neutrons. Correction: the atomic number is the proton count; the neutron number is found by subtracting the atomic number from the mass number.
- Saying that electrons orbit the nucleus like planets orbit the Sun in fixed paths. Correction: 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. Correction: the nucleus is very small and dense, while electrons occupy most of the atom's volume.
- Stating that neutrons are positively charged. Correction: neutrons are neutral, protons are positive and electrons are negative.