3.2.1.1
Atoms are made of protons, neutrons and electrons
Atomic Structure & Nuclear Stability — AQA A-Level Physics
- All matter is made from atoms.
- Protons and neutrons sit in the nucleus. Electrons orbit the nucleus.
- A stable atom is electrically neutral — equal numbers of protons and electrons.
Properties in SI units
- Proton: chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). $= +1.60 \times 10^{-19}$ C, mass $= 1.67(3) \times 10^{-27}$ kg.
- Neutron: chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). $= 0$, mass $= 1.67(5) \times 10^{-27}$ kg.
- Electron: chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). $= -1.60 \times 10^{-19}$ C, mass $= 9.11 \times 10^{-31}$ kg.
Relative properties
- Proton: relative charge $= +1$, relative mass $= 1$.
- Neutron: relative charge $= 0$, relative mass $= 1$.
- Electron: relative charge $= -1$, relative mass $\approx 1/2000$ (negligible).
Examiner Tips and Tricks
- Don't mix up 'atom' and 'nucleus'.
- The atom includes the nucleus and the electrons.
- The nucleus is just the protons and neutrons in the middle.