A hydrogen atom has one proton. A helium atom has two protons.
The mass of a helium atom is about four times the mass of a hydrogen atom.
Rutherford's nuclear model could not explain this.
Which later discovery explained it?
The nucleus also contains neutral particles with a similar mass to a proton.
The protons in a helium atom have twice the mass of the protons in a hydrogen atom.
Helium atoms contain four electrons, and each one has a similar mass to a proton.
The nucleus also contains electrons, which add to the mass of the atom.
101 exam-style questions on OCR GCSE Chemistry 1.2 Atomic structure, covering 1.2.1 Development of the atomic model, 1.2.2 The nuclear model and the size of atoms, and 1.2.3 Subatomic particles in atoms and ions. Each one has a worked solution and a mark scheme showing where the marks go.