Atoms, Elements and Compounds – Atomic Structure & Periodic Table
Objective
State the relative charges and relative masses of a proton, a neutron and an electron. ⚛️
What are the tiny building blocks?
Think of an atom as a tiny solar system:
- 🌞 The nucleus is the bright sun – it contains protons (positive) and neutrons (neutral).
- 🌑 The electrons are tiny moons that orbit far away, carrying a negative charge.
- ⚖️ The mass of the atom is almost entirely in the nucleus; electrons are almost massless.
Charges – How do they compare?
The elementary charge \$e\$ is the basic unit of electric charge.
- Proton: \$+1\,e\$ (positive)
- Electron: \$-1\,e\$ (negative)
- Neutron: \$0\,e\$ (neutral)
Masses – How big are they?
Mass is measured in atomic mass units (amu).
- Proton: \$1.0073\,\text{amu}\$
- Neutron: \$1.0087\,\text{amu}\$
- Electron: \$0.0005\,\text{amu}\$ (almost nothing!)
The proton and neutron are roughly the same size, but the neutron is slightly heavier. The electron is about 1/1836 the mass of a proton.
Quick Reference Table
| Particle | Charge (\$e\$) | Relative Mass (amu) |
|---|
| Proton | \$+1\$ | 1.0073 |
| Neutron | \$0\$ | 1.0087 |
| Electron | \$-1\$ | 0.0005 |
Exam Tips
- Write the charge of a proton as \$+1\,e\$, electron as \$-1\,e\$, neutron as \$0\,e\$.
- Remember the relative mass of an electron is negligible – it can be omitted when calculating atomic mass.
- Proton and neutron masses are both about 1 amu; the neutron is slightly heavier.
- Use the table to quickly check values during revision.
- Practice converting between charge units and mass units in past exam questions.