AQA GCSE Mass number and Atomic Number

AQA GCSE Mass number and Atomic Number

Mass Number and Atomic Number

The periodic table lists the elements, each element has a symbol with two numbers. One number is above the symbol and the other number is below the symbol.

Chemical element symbol showing both the mass number and the atomic number, using lithium as an example

The mass number is the total number of protons and neutrons

The atomic number is the number of protons in an atom of the element. All atoms of the same element have the same number of protons.

Number of Neutrons = Mass number – Atomic number.

Overall charge of an atom

Atoms have no overall electrical charge.

Each proton has a +1 charge and each electron a -1 charge.

Structure of the atom

 

In a neutral atom the number of electrons in an atom is equal to the number of protons in the nucleus

Practice Questions

1. Using a periodic table, write down the mass number and atomic number of Fluorine. 

If you do not have access to a periodic table, you can use the AQA one here

2. How many neutrons are in an atom of Phosphorous-31?

3. Explain why Aluminium atoms are electrically neutral

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