9701 · 1.1
Particles in the atom and atomic radius
Atoms are built from simple rules involving protons, neutrons, and electrons. These rules determine an element's identity, mass, and size.
Need to know
What you need to know
- Proton (p): Relative mass = 1, Relative charge = +1
- Neutron (n): Relative mass = 1, Relative charge = 0
- Electron (e⁻): Relative mass ≈ 1/1840 (negligible), Relative charge = -1
Explanation
The Atom's Blueprint
- Atoms contain protons and neutrons in the nucleus, electrons in shells.
- Atomic number Z = proton number; mass number A = protons + neutrons.
- Ions form when electrons are gained or lost — charge = protons − electrons.
- Atomic radius decreases across a period (increasing nuclear charge).