Atoms are built from three subatomic particles
Definition
Subatomic particle
A particle smaller than an atom that forms part of its structure, such as a proton, neutron or electron.
- Every atom is made of three subatomic particles: protons, neutrons and electrons.
- Protons and neutrons are found together in the central nucleus.
- Electrons move around the nucleus in energy levels (shells).
- Each particle carries a relative electrical charge, measured against the charge on a proton.
- A proton has a relative charge of +1+1+1.
- A neutron has a relative charge of 000, so it is neutral.
- An electron has a relative charge of −1-1−1, equal and opposite to a proton.
Key Idea
- Charges are relative: the proton is set to +1+1+1 and every other charge is compared with it.
- The proton and electron carry equal but opposite charges.
Equal protons and electrons make an atom neutral
Definition
Relative electrical charge
The electrical charge of a particle compared with the charge of a proton, which is assigned a value of +1.
- In any neutral atom, the number of protons equals the number of electrons.
- The total positive charge from the protons is cancelled by the total negative charge from the electrons.
- This is why an atom has no overall charge.
- For example, a sodium atom has 11 protons and 11 electrons, so its charges cancel exactly.
- If an atom loses or gains electrons, the numbers no longer match and it becomes a charged ion.
- Do not confuse a neutron with a neutral atom: a neutron is one uncharged particle, while a neutral atom is uncharged because its protons and electrons balance.
Self review
- What is the relative charge of a proton, a neutron and an electron?
- Answer: +1+1+1, 000 and −1-1−1.
- Where in the atom are protons and neutrons found?
- Answer: together in the nucleus.
- Why does a neutral atom have no overall charge?
- Answer: it has equal numbers of protons and electrons, so the charges cancel.
- A sodium atom has 11 protons. How many electrons does it have?
- Answer: 11 electrons.
