chemistry revision

compounds are substances in which elements are chemically combined.

the noble gases are unreactive because their atoms have stable arrangements of electrons. atoms of other elements can achieve stable electronic structures by gaining/losing electrons to form ions or by sharing to form covalent bonds.

compounds made of ions have giant structures that are very regular

ionic bonding holds two oppositley charged ions together in giant structures. strong electromagnetic forces of attraction act in all directions. each ion in the lattice is surrownded by ions with the opposite charge and so is held firmly in place.

a covalent bond is formed when two atoms share a pair of electrons.

the number of covalent bonds an atom forms depends on the number of electrons it needs to achieve a stable electron arrangement.

many covalently bonded substances consist of small molecules but some have giant structures.

the atoms in metallic elements are all the same size.

metals have giant structures of layers of atoms arranged in a regular pattern.