How do you read the periodic table?

Each box has an element’s symbol in the middle. The small number at the bottom is the atomic number (the number of protons), and the number at the top is the relative atomic mass. Rows are periods and columns are groups.

How do I work out the number of neutrons?

Take the atomic number away from the mass number. Sodium has a mass number of 23 and an atomic number of 11, so it has 23 − 11 = 12 neutrons.

Why is chlorine’s relative atomic mass 35.5?

Chlorine has two isotopes, chlorine-35 and chlorine-37. About three quarters of chlorine atoms are chlorine-35, so the average mass is 35.5.

What does the group number tell you?

For groups 1 to 7, the group number is the number of electrons in the outer shell. Elements in the same group react in similar ways. Group 0 (the noble gases) have a full outer shell, so they’re unreactive.

Do I get a periodic table in the GCSE chemistry exam?

Yes. AQA, Edexcel and OCR all give you one with the exam, laid out like this one, so you don’t have to learn the masses.

Revision tools

The periodic table

Laid out like the one you get in the GCSE chemistry exam. Press any element to see its protons, neutrons, electrons and group.

Swipe sideways to see the whole table.

12345670Transition metals58–7190–103

Press an element to see its protons, neutrons, electrons and group.

Alkali metals (group 1)
Group 2 metals
Transition metals
Other metals
Metalloids
Non-metals
Halogens (group 7)
Noble gases (group 0)
Lanthanides
Actinides

How to read it

Top: 23 is the relative atomic mass. For most elements it’s the mass number (protons + neutrons).

Middle: Na is the symbol for sodium.

Bottom: 11 is the atomic number: the number of protons, and of electrons in a neutral atom.

So sodium has 11 protons, 11 electrons and 23 − 11 = 12 neutrons.

Rows are periods: the period number is how many shells of electrons an atom has. Columns are groups: for groups 1 to 7, the group number is how many electrons are in the outer shell, which is why elements in a group react in similar ways.

Revise it

Questions

How do you read the periodic table?: Each box has an element’s symbol in the middle. The small number at the bottom is the atomic number (the number of protons), and the number at the top is the relative atomic mass. Rows are periods and columns are groups.
How do I work out the number of neutrons?: Take the atomic number away from the mass number. Sodium has a mass number of 23 and an atomic number of 11, so it has 23 − 11 = 12 neutrons.
Why is chlorine’s relative atomic mass 35.5?: Chlorine has two isotopes, chlorine-35 and chlorine-37. About three quarters of chlorine atoms are chlorine-35, so the average mass is 35.5.
What does the group number tell you?: For groups 1 to 7, the group number is the number of electrons in the outer shell. Elements in the same group react in similar ways. Group 0 (the noble gases) have a full outer shell, so they’re unreactive.
Do I get a periodic table in the GCSE chemistry exam?: Yes. AQA, Edexcel and OCR all give you one with the exam, laid out like this one, so you don’t have to learn the masses.