<span> Atoms combine as the electrons from each atom are attracted to the nuclei of the atoms. This results in bonds ranging from 100% covalent to bonds with high ionic character. The combination of atoms to form compounds occurs when the compounds being formed are at lower energy than the original atoms.</span>
H2O became a vapor when heated because thats the only one that can go back to its normal state, which is what a physical change is.
Zn(s) + 2 HCl(aq) → ZnCl₂(aq) + H₂(g)
Oxidation means lose of electrons and increase of positive charge so the part which oxidized in this equation is Zn(s) because it converted to Zn²⁺ (i.e. lost two electrons)
