Chemistry Atomic Structure 1
Each atom consists of a nucleus containingprotons and neutrons, with electrons arranged around it in energy levels.
Name of particleRelative mass Proton 1 Neutron 1 Electron Very small (1/1836)
The atoms of a particular element will all have the same number of protons. Their atomic number will be the same. However, the atoms of an element can have different numbers of neutrons - so their mass numbers will be different.
The full chemical symbol for an element shows its mass number at the top, and atomic number at the bottom. Here is the full symbol for carbon:
The symbol also tells us that the total number of protons and neutrons in a carbon atom is 12. Note that you can work out the number of neutrons from the mass number and atomic number. In this example, it is 12 – 6 = 6 neutrons.