Subatomic Particles | Chemistry

📖 In-Depth Theory

The Three Subatomic Particles

Every atom contains three types of subatomic particle:

PROTON:

Found in the NUCLEUS.

Relative charge: +1.

Relative mass: 1.

NEUTRON:

Found in the NUCLEUS.

Relative charge: 0 (neutral).

Relative mass: 1.

ELECTRON:

Found in SHELLS (energy levels) around the nucleus.

Relative charge: −1.

Relative mass: approximately 1/1836 — effectively 0 in relative terms.

Atoms are electrically NEUTRAL because the number of protons = number of electrons (positive and negative charges cancel).

The NUCLEUS contains protons and neutrons — almost all of the atom's mass is concentrated here.

Electrons contribute negligible mass.

Ions — When Atoms Gain or Lose Electrons

An ION is a charged particle formed when an atom gains or loses electrons.

ATOM LOSES ELECTRONS → positive ion (cation)

Example: Na → Na⁺ + e⁻ (sodium loses 1 electron → +1 charge)

Example: Mg → Mg²⁺ + 2e⁻ (magnesium loses 2 electrons → +2 charge)

ATOM GAINS ELECTRONS → negative ion (anion)

Example: Cl + e⁻ → Cl⁻ (chlorine gains 1 electron → −1 charge)

Example: O + 2e⁻ → O²⁻ (oxygen gains 2 electrons → −2 charge)

The charge on an ion tells you how many electrons were gained or lost.

The NUMBER OF PROTONS never changes in a chemical reaction — only electron numbers change.

Size and Scale of Atoms

Atoms are incredibly small — they cannot be seen with a light microscope.

A typical atomic radius ≈ 1 × 10⁻¹⁰ m (0.1 nanometres).

A human hair is about 1 million atoms wide.

A grain of sand contains approximately 10¹⁸ atoms.

The NUCLEUS is even smaller — about 10,000 times smaller than the whole atom:

Nuclear radius ≈ 1 × 10⁻¹⁴ m

This means the atom is almost entirely EMPTY SPACE — the nucleus is tiny compared to the overall size of the atom, with electrons in the vast space around it.

This is consistent with what Rutherford found — most alpha particles passing straight through gold foil without hitting anything.

⚠️ Common Mistake

The number of PROTONS never changes in a chemical reaction — only electrons are gained or lost to form ions. Also: electrons have negligible mass — almost all atomic mass is in the nucleus (protons + neutrons both have relative mass 1). The atom is MOSTLY EMPTY SPACE — the nucleus is 10,000 times smaller than the atom.

📌 Key Note

Proton: +1, mass 1, nucleus. Neutron: 0, mass 1, nucleus. Electron: −1, mass ~0, shells. Neutral atom: protons = electrons. Atom loses electrons → positive ion. Atom gains electrons → negative ion. Atom mostly empty space — nucleus is tiny.

🎯 Matching Activity — Match the Subatomic Particle

Match each particle to its charge, mass and location. — drag the symbols on the right to match the component names on the left.

Proton

Drop here

Neutron

Drop here

Electron

Drop here

Na⁺ ion

Drop here

Cl⁻ ion

Drop here

Relative charge +1, mass 1 — in the nucleus

Sodium atom that has LOST one electron — 11 protons, 10 electrons

Relative charge 0, mass 1 — in the nucleus

Chlorine atom that has GAINED one electron — 17 protons, 18 electrons

Relative charge −1, mass ~0 — in shells around the nucleus

🎯 Test Yourself

Question 1 of 2

1. A magnesium atom (Mg, atomic number 12) forms a Mg²⁺ ion. How many electrons does the ion have?

2. Why does an atom have no overall electrical charge?

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🧪 Subatomic Particles

The Three Subatomic Particles

Ions — When Atoms Gain or Lose Electrons

Size and Scale of Atoms

Mr. Badmus AI