Question

discuss how atoms unite and change into molecules

Answer 1

A molecule is simply a unit comprised of atoms bonded together. Converting between the two isn't a traditional conversion except in certain cases, such as Hydrogen gas (H2) or Oxygen gas (O2), where the molecule is made entirely of the same atom. In cases like this, the subscript tells you that, for example, Oxygen gas (a molecule) is made of 2 Oxygen atoms. Converting from one to the other is as simple as multiplying by 2.