How are atoms and molecules related?

Molecules are groups of atoms that have chemically bonded together.

A chemical bond is where one atom sticks to another.

Atoms are themselves groups of particles. They have protons and neutrons in a heavy solid mass in the middle known as the nucleus, with electrons orbiting the outside. Protons are positive and neutrons have no charge - neutrons are practically lumps of rock on the subatomic scale - so the nucleus is overall positive, while the orbiting electrons are negative.

Atoms have the same number of protons and electrons. Electrons are organised into shells or energy levels, which only have certain capacities - when one is full, you have to start putting electrons on the next shell out. Atoms would like their outer or valence shell to be full, because that means they are stable - they don't react any more.

When atoms bonds, they share or give away electrons to other atoms to fill their outer shells. Covalent is when they share, which binds two atoms together, because without the other, neither would have a satisfied outer shell. Covalently bonded atoms are look blood brothers.

Ionic bonds are more like blood donors. These occur only between metal and non-metal atoms. The metal gives away its extra electrons to the non-metal, which means the metal becomes more positive (as it loses a negative thing, and ##-- = +##) and the non-metal becomes negative. Like North and South on magnets, the positive and negative ions stick together. An ion is an atom which has a different number of electrons to protons, and so has a positive or negative electrical charge.

Exclusively between metals you can have a third type of bonding - metallic. This is where the metals give up their extra electrons which float around freely - thus allowing metals to conduct heat and electricity, which is energy that passes through, carried by free electrons. Because electrons are negative and the metal nuclei are positive, they are attracted to each other, and metals stick together around this sea of electrons.

Through these types of bonding, atoms can stick together to form molecules.