Trends of Period 3 Elements: Atomic Radius

Question 1

The atomic radius is the distance between the nucleus and the outermost electron of an atom

The atomic radius is measured by taking two atoms of the same element, measuring the distance between their nuclei and then halving this distance

In metals this is also called the metallic radius and in non-metals, the covalent radius

Question 2

Across period 3 the atomic radius …….

Answer 2

decreases

Question 3

Why does period 3’s atomic radius decrease across period

Answer 3

This is because the number of protons (the nuclear charge) and the number of electrons increases by one every time you go an element to the right

The elements in a period all have the same number of shells (so the shielding effect is the same)

This means that as you go across the period the nucleus attracts the electrons more strongly pulling them closer to the nucleus

Because of this, the atomic radius (and thus the size of the atoms) decreases across the period