5.1.1.4Relative electrical charges of subatomic particles
AQA GCSE Combined Science Foundation (8464), Foundation tier · Chemistry › Atomic structure and the periodic table › A simple model of the atom, symbols, relative atomic mass,
Practise Relative electrical charges of subatomic particles. 6 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
The relative charges of protons, neutrons and electrons, why atoms have no overall charge, and what the atomic number tells you. Questions are usually short: complete a table, use an atomic number, or explain why an atom is neutral.
Key facts
Proton: relative charge +1, in the nucleus
Neutron: relative charge 0, in the nucleus
Electron: relative charge −1, in shells around the nucleus
In an atom: number of electrons = number of protons, so no overall charge
Atomic number = number of protons
Overall charge = protons − electrons
Notes
The three subatomic particles
diagram
Proton: relative charge +1, found in the nucleus.
Neutron: relative charge 0 (neutral), found in the nucleus.
Electron: relative charge −1, found in shells (energy levels) around the nucleus.
The nucleus is positive overall, because it contains positive protons and neutral neutrons.
A lithium atom: 3 protons, 4 neutrons, 3 electrons. It has no overall charge.
Why atoms have no overall charge
In an atom, the number of electrons is equal to the number of protons.
Each +1 charge is cancelled by a −1 charge, so the atom has no overall electrical charge.
If an atom loses or gains electrons, it becomes an ion with an overall charge. The number of protons does not change.
Overall charge = number of protons − number of electrons.
Atomic number
The atomic number of an element is the number of protons in each of its atoms.
All atoms of a particular element have the same number of protons, e.g. every carbon atom has 6.
Atoms of different elements have different numbers of protons, so the atomic number tells you which element an atom is.
Because atoms are neutral, the atomic number also tells you the number of electrons in an atom (but not in an ion).
The periodic table lists the elements in order of atomic number.
How to answer each type of question
Complete a table of charges and positions
2 to 3 marksGrade 3
Charges: proton +1, neutron 0, electron −1 (include the sign).
Positions: protons and neutrons in the nucleus; electrons in shells around the nucleus.
Example. Complete the table.
Particle
Relative charge
Where it is found
Proton
......
in the nucleus
Neutron
0
......
Electron
......
......
Show the model answerHide the model answer
Particle
Relative charge
Where it is found
Proton
+1
in the nucleus
Neutron
0
in the nucleus
Electron
−1
in shells / energy levels around the nucleus
Proton charge +1 (1); neutron in the nucleus (1); electron −1 and in shells around the nucleus (1).
Explain why an atom has no overall charge
2 marksGrade 5
State the number of electrons and say it equals the number of protons.
Say that the positive and negative charges cancel (neutrons have no charge).
Example. An atom of fluorine has 9 protons. Explain why the atom has no overall charge.
Show the model answerHide the model answer
The atom has 9 electrons, the same number as protons (1). The +9 charge of the protons is cancelled by the −9 charge of the electrons, and neutrons have no charge (1).
Use the atomic number
1 mark eachGrade 5
In an atom, atomic number = protons = electrons.
Find the element with that atomic number in the periodic table.
Example. An atom has 19 electrons. (a) Give the atomic number of the element. (b) Use the periodic table to name the element. (c) Explain why every atom of this element has the same atomic number.
Show the model answerHide the model answer
(a) 19 (1) (b) potassium (1) (c) All atoms of an element have the same number of protons (1).
Don’t lose marks
Giving the neutron a charge of −1 or +1. Its relative charge is 0.
Saying atoms are neutral because they have equal numbers of protons and neutrons. It is protons and electrons.
Giving the mass number when the question asks for the atomic number.
Saying ions form by gaining or losing protons. Only electrons are gained or lost.
More tips
Memory tricks
Positive Proton, Neutral Neutron; the electron is the negative one.
Atomic number is the smaller of the two numbers in a nuclear symbol or periodic table box (they are only equal for hydrogen).
Charge on a particle: protons minus electrons.
Exam technique
Give relative charges as +1, 0 and −1, with the sign and without units.
When explaining why an atom is neutral, name both particles and use the words 'equal number'.
Use the periodic table on the data sheet to look up atomic numbers.
What each grade needs
What you need to be able to do, from the first marks up to the top grade.
Grade 3
Recall the charges of subatomic particlesProton +1, neutron 0, electron −1.
Grade 3
State where each particle is foundProtons and neutrons are in the nucleus; electrons are in shells around it.
Grade 4
Define atomic numberThe number of protons in an atom; all atoms of the same element have the same number.
Grade 5
Explain why atoms have no overall chargeThe number of electrons equals the number of protons, so the charges cancel.
Grade 5
Identify an element from its proton numberDifferent elements have different numbers of protons, so the atomic number tells you the element.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
An atom of fluorine has 9 protons. How many electrons does it have?
9
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy6 marks
Atoms contain protons, neutrons and electrons. A proton has a relative charge of +1.
(a) What is the relative charge of a neutron? Tick (✓) one box.[1]
−1
0
+1
+2
(b) What is the relative charge of an electron? Tick (✓) one box.[1]
−1
0
+1
+2
(c) Explain why an atom has no overall electrical charge.[2]
(d) An atom of fluorine has 9 protons. How many electrons does it have?[1]
(e) What name is given to the number of protons in an atom?[1]
Show the answer and mark scheme
(a)Answer: 0
(b)Answer: −1
(c)Answer: The number of electrons equals the number of protons, so the positive and negative charges cancel.
number of electrons = number of protons
so the (positive and negative) charges cancel (out)
(d)Answer: 9
9
(e)Answer: atomic number
atomic number
Question 2Medium5 marks
A magnesium atom has 12 protons. It can lose two electrons to form a magnesium ion.
(a) How many electrons does a magnesium atom have?[1]
(b) Use the relative charges of protons and electrons to calculate the charge on a magnesium ion. Show your working.[2]
(c) An oxide ion has 8 protons and a charge of 2−. How many electrons does an oxide ion have?[1]
(d) Explain why a magnesium ion has almost the same mass as a magnesium atom.[1]