Particles in the atom
| English | Chinese | Pinyin |
|---|---|---|
| atom | 原子 | yuán zi |
| nucleus | 原子核 | yuán zǐ hé |
| proton | 质子 | zhì zi |
| neutron | 中子 | zhōng zi |
| electron | 电子 | diàn zi |
| shell | 壳层 | ké céng |
| proton number | 质子数 | zhì zi shù |
| nucleon number | 核子数 | hé zǐ shù |
| ion | 离子 | lí zi |
Inside the atom 原子
- Everything is made of atoms — and an atom is mostly empty space.
- At the centre is a tiny, heavy nucleus 原子核 of protons 质子 and neutrons 中子.
- Electrons 电子 move around it in shells 壳层.
A proton has a relative charge of +1 and a neutron has no charge.
Electrons carry −1; protons +1; neutrons 0.
The three particles
| Particle | Relative charge | Relative mass |
|---|---|---|
| proton | +1 | 1 |
| neutron | 0 | 1 |
| electron | −1 | ~1/1836 (≈ 0) |
- The nucleus is tiny but holds almost all the mass.
- The electrons take up almost all the space but have almost no mass.
An atom: a tiny nucleus of protons and neutrons, with electrons in shells
Explore the atom
Tap each part. A tiny dense nucleus of protons and neutrons holds the mass; light electrons orbit it in shells.
Which particle has a relative charge of 0 and a relative mass of 1?
A neutron is neutral (charge 0) with relative mass 1; the proton is +1 mass 1; the electron is −1 and almost massless.
Match each particle to its relative charge and mass.
Protons and neutrons (mass 1 each) sit in the nucleus; the much lighter electrons orbit it.
Counting particles
- proton number 质子数 $Z$ = number of protons (also the atomic number).
- nucleon number 核子数 $A$ = protons + neutrons (also the mass number).
- So neutrons $= A - Z$. In a neutral atom, electrons $= Z$.
- An ion 离子 has gained/lost electrons: e.g. $^{27}_{13}\text{Al}^{3+}$ has 13 protons, 14 neutrons, and $13-3 = 10$ electrons.
Each element emits light at characteristic wavelengths: its emission spectrum
The number of neutrons in an atom is:
A counts protons + neutrons and Z counts protons, so neutrons = A − Z.
How many electrons does the ion ²⁷₁₃Al³⁺ have?
A neutral Al atom has 13 electrons; the 3+ ion has lost 3, leaving 13 − 3 = 10.
Beams in an electric field
- Fire proton, neutron and electron beams between charged plates:
- the proton bends gently towards the − plate.
- the electron bends the other way (to +) and far more — it is much lighter.
- the neutron goes straight through (no charge).
Proton, electron and neutron beams in an electric field
In an electric field, which beam is deflected the most?
The same force gives a bigger deflection to a smaller mass, so the light electron bends most; the neutron goes straight.
You've got it
- proton (+1, mass 1), neutron (0, mass 1), electron (−1, ≈ 0)
- $Z$ = protons; $A$ = protons + neutrons; neutrons $= A - Z$; neutral atom electrons $= Z$
- an ion has lost/gained electrons (e.g. $\text{Al}^{3+}$ has 3 fewer electrons)
- in a field: electron deflects most, proton the other way, neutron straight