Maybe this example could help you to understand this problem.
https://image.slidesharecdn.com/121howmanyatoms-091201144624-phpapp02/95/12-1-how-many-atoms-17-728....
Accept a pair of nonbonding electrons,a Lewis acid is an electron-pair acceptor. A Lewis<span> base is any </span>substance, such as the OH-<span> ion, that </span>can<span> donate a pair of nonbonding electrons. </span>A Lewis<span> base is therefore an electron-pair donor.</span>
Binary compounds consist of only two distinct elements, regardless of whether the compound is ionic or molecular. Water is a binary compound, as are calcium chloride, ammonia, and potassium iodide.
<span>An ionic binary compound consists of cations of one element and anions of another. KI is an ionic binary compound, composed of K cations and I anions. </span>
<span>A molecular binary compound does not consist of discrete ions, but of molecules. H2O is molecular, as is NH3.</span>
A balanced equation must have the same number of atoms on the both sides of equation.
