1.1 particles in the atom and atomic radius

1 describe the structure of an atom

Mostly empty space surrounding a very small, dense nucleus that contains protons and neutrons.

Electrons are found in shells in the empty space around the nucleus

2. Identify and describe protons, neutrons and electrons in terms of their relative charges and relative masses

3. Define atomic number

Number of protons

3. Define mass number

Number of protons and neutrons

4 Describe the distribution of mass and charge within an atom

Mass of electrons are neglible compared with masses of protons and neutrons. Therefore almost all mass is concentrated in nucleus

In an electrically neutral atom, there must be same numbers of protons and electrons.

5. Describe the behaviour of beams of protons, neutrons and electrons present moving at the same velocity in an electrically neutral atom field.

Protons are deflected on a curving path towards the negative plate

Electrons are deflected on a curving path away from the negative plate towards the positive plate

Neutrons have no charge so continue in straight line

Explain the variations in atomic radius across a period

Atomic radius decreases across a period due to an increase in protons in the nucleus

Therefore an increase in nuclear charge which attracts outer electrons more strongly.

Explain the variations in ionic radius across a period

Decreases for positive ions but increases for negative ions

Positive ions have a decreasing ionic radius as although ions have same electron configuration, number of protons has increases so nuclear attraction increases.

Negative ions have an increasing ionic radius as ions have gained electrons meaning that there are more electrons that protons. Therefore, nuclear attraction decreases

Explain the variations in atomic radius down a group

Increases as there is an increases number of shells

Electrons in inner shells repel the electrons in the outermost shells, shielding them from the positive nuclear charge

Explain the variations in ionic radius down the group

Increases going down the group due to increased shielding