Atoms & Elements Basics

Think of atoms like tiny LEGO blocks that make up everything in the universe. Atoms are the smallest units of elements (pure substances with specific properties), and they're made up of three main subatomic particles that work together perfectly.

Protons have a +1 charge and live in the nucleus (centre) of the atom. Neutrons are neutral (0 charge) and also hang out in the nucleus. Electrons have a -1 charge and zip around the nucleus in electron shells. Here's the clever bit: protons and neutrons each have a mass of 1, whilst electrons are so light they're practically weightless $1/2000$.

The atomic number tells you how many protons an element has, and this number never changes for that element. Carbon always has 6 protons, for example. Since atoms are neutral overall, the number of electrons equals the number of protons.

Quick Tip: The atomic mass number tells you the total of protons + neutrons. So if carbon has atomic mass 12 and 6 protons, it must have 6 neutrons!

Valency is an element's combining power - basically how it bonds with other elements. Elements in the same group (column) on the periodic table have the same valency because they behave similarly. Non-metals gain electrons to fill their outer shells and become negative ions, whilst metals lose electrons and become positive ions.