Notes

In nature, atoms are not separate particles, but bond together to become more stable. The product of two atoms bonded together is a molecule.
The outer electrons (valence electrons) of atoms determine the reactivity of an atom. The periodic table shows trends in chemical properties that can be explained by the trends in the number of valence electrons.
Lewis structures are visual models showing the valence electrons of an atom.
The octet rule can be used to predict how an element will gain, lose, or share electrons in order to achieve a more stable state.

Atoms form bonds with other atoms using the valence electrons in their outer energy levels. An atom can form bonds in different ways: it can lose electrons, gain electrons, or share electrons with another atom.

Atoms very rarely exist as individual particles. Most substances you can think of are made up of combinations of atoms that are held together by chemical bonds. These bonds form because most atoms are more stable when they are bonded to other atoms. During the formation of a chemical bond, valence electrons rearrange themselves into a more stable configuration.

Most chemical bonds can be described as either ionic bonds or covalent bond.

An ionic bond is the attraction of a positively charged ion to a negatively charged ion. Because of this opposite attraction, ionic bonds are very strong. When atoms combine in an ionic bond, an ionic compound is formed.