Chemistry - Paper 1

Who invented the fist atomic model?

John Dalton

What is Dalton’s model about?

Atoms were believed to be tiny spheres that could not be divded

Who discovered the Plum Pudding Model?

JJ Thomson

What did Thomson discover?

He discovered the electron and proposed that atoms were balls of positive charge with embedded negative electrons.

Who discovered the nuclear model?

Ernest Rutherford

What did Rutherford discover?

He conducted the alpha scattering experiment and found that the mass of the atom was concentrated at its centre in a positively charged nucleus.

• most particles pass through so the atom is mostly empty space

• a small number of alpha particles being deflected suggested that there is a concentration of positive charge in the atom

• the very small number of alpha particles coming straight back suggested that the positive charge and mass are concentrated in a tiny nucleus

What did Bohr discover?

Electrons orbit the nucleus in shells and in fixed energy levels and distances

Who discovered protons?

Rutherford

Who discovered the neutrons?

James Chadwick

Who invented the modern periodic table?

Dmitri Mendeleev

Explain the reactivity of group 1 and 7

In Group 1, atomic size increases as you go down, so atoms have more electron shells. This means the outer electron is further from the nucleus, and the electrostatic attraction is weaker, making it easier to lose that electron — so reactivity increases.

In Group 7, atomic size also increases, meaning more shielding and a weaker attraction between the nucleus and an incoming electron. This makes it harder to gain an electron, so reactivity decreases down the group.