All things around us are made of atoms. The clothes we wear, the buildings we live in, the air around us, even our own bodies. Atoms are the microscopic building blocks of every solid, liquid or gas. If all the atoms in a substance are the same type – it is called an element. This means it cannot be broken down into any “ingredients”. Oxygen (chemical symbol O) is a pure element. Oxygen is oxygen – it is not made up of anything else. If a substance contains more than one element, it is either a compound or a mixture. We will discuss these later, for now let’s stick to elements.
We said before that elements have no “ingredients” – but actually they do. Even a tiny atom is built of smaller building blocks. All atoms are built of 3 basic things : Protons, Neutrons, and Electrons.
The simplest atom is Hydrogen. A hydrogen atom is built of one proton and one electron. The proton sits in the centre of the atom and forms the nucleus of hydrogen. The electron spins around the nucleus – a bit like a moon orbiting a planet. Hydrogen, as you can see in the diagram below, does not have any neutrons. Larger atoms have many protons and neutrons in their nucleus, and have many orbiting electrons.
So why doesn’t the electron just spin off ? Why does it stay orbiting the nucleus?
The answer is that the electron is attracted to the nucleus because of its ‘charge’. Electrons have a negative charge and protons have a positive charge (neutrons do not have a charge). Opposite charges attract each other.
Need help to understand charge attraction? This is why clothing taken from the drying machine ‘clings’. A static charge is formed when the clothing rubs together in the machine, and this builds up a negative charge. The negative clothing is then attracted to more positively charged things around it.
The force caused by the spinning, which should cause the electron to spin off away from the nucleus, is balanced by the charge force attracting the electron towards the nucleus. So it doesn’t fly off OR cling to the nucleus, it spins around being pulled equally in both directions.
Although the proton has a positive charge, and the electron has a negative charge, the atom itself has no charge – it is neutral. All atoms have the same number of negative orbiting electrons as they have positive protons in their nucleus (each ‘+’ is cancelled out by a ‘-‘). If you have trouble grasping this – just do the maths. Every proton is +1, every electron is -1, and the total of all protons and electrons has to be zero.