atoms and elements heading

Foundation and higher tiers

You could be asked to draw or describe the atomic structure of any element up to element 20, calcium in your GCSE exam. Drawing atomic structure diagrams for atoms is very easy once you get the hang of it e.g. Find the element magnesium on the periodic table. The two numbers beside the element symbol are called the atomic number and the **mass number. These two numbers allow you to calculate the number of protons, neutrons and electrons inside the atom.

magnesium symbol

Calculating the number of protons, neutrons and electrons

So for magnesium its atomic number is 12, this means it has 12 protons in its nucleus. In an atom the number of protons always equals the number of electrons, so magnesium has 12 electrons. To calculate the number of neutrons inside the atom we simply take the atomic number from the mass number.....
calcualte number of neutrons Since the mass number is 24 and the atomic number is 12 we simply subtract 12 from 24, to leave 12 neutrons. So an atom of magnesium has 12 protons, 12 electrons and 12 neutrons.

atomic structure diagram for magnesium

Below is one more example just to make sure are confident calculating the numbers of protons, neutrons and electrons inside atoms as well as drawing out atomic structure diagrams.

carbon symbol

So the carbon atom has 6 protons, 6 electrons and 6 neutrons. The protons and neutrons will go inside the nucleus. The 6 electrons will go into the electron shells, 2e in the first shell leaving 4 for the second shell. This gives carbon an electron arrangement of 2,4.

atomic structure diagram for carbon

Calculating the numbers of protons, electrons and neutrons in ions

An ion is a cgarged atom. Atoms have no charge since they contain equal numbers of positively charged protons in their nucleus and negatively charged electrons in the electron shells. However when elements react with each other they transfer electrons. Metal atoms tend to lose electrons and form ions with a positive charge. While non-metals gain electrons and form ions with a negative charge.

Key points

Practice questions

Check your understanding - complete the following practice questions