Ions: charged atoms or molecules, e.g. salt solution with sodium and chlorine ions.
Ionic Bond: The bond between atoms in which electrons are donated by one element to another. For example salt: NaCl.
Covalent Bond: The bond formed between atoms in which electrons are shared. For example molecular oxygen: O2, water: H2O.
Metallic Bonds: Similar to covalent bonds except that the electrons are shared among all the atoms in a sample of metal. This bonding gives metals their unique physical and electrical properties.
Isomers: Chemicals with the same elemental composition but different bonding structures
Hydrogen bond: The weaker bonding due to the attraction of a positive hydrogen atom in a chemical with a negative "pole" of another molecule.
Atomic weight: the relative weight of the atom of an element (relative to C=12).
Atomic number: The number of protons in the nucleus of the atoms of the elements.
Isotope. Atoms of the same element (same atomic number) but with different atomic weights, so that they have different numbers of neutrons, are different isotopes of the same element.
Mole: Avogadro's number of particles. It is defined so that a mole of atoms of an element weighs in grams the numerical value of its atomic weight.
Fact: A mole of C weighs 12 grams,...etc.
Practice stoichiometry problems!