You are here: Home > A Level > Inorganic Chemistry (Core) > Periodicity > Atomic radius across period 3
After studying this page, you should be able to:
Element | Symbol | Atomic number | Atomic radius /nm |
---|---|---|---|
Sodium | Na | 11 | 0.191 |
Magnesium | Mg | 12 | 0.160 |
Aluminium | Al | 13 | 0.130 |
Silicon | Si | 14 | 0.118 |
Phosphorus | P | 15 | 0.110 |
Sulfur | S | 16 | 0.102 |
Chlorine | Cl | 17 | 0.099 |
Argon | Ar | 18 | 0.095 |
The graph shows how atomic radius varies across period 3:
When you click on the download symbol, you will be able to download the graph as an image file or pdf file, save its data, annotate it, and print it.
Going across period 3:
You might expect the atomic radius to increase because the number of electrons in each atom increases going across period 3. However, this does not happen: the number of protons also increases and there is relatively little extra shielding from electrons in the same shell.
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