-why we dont mention any charges in a chemical compound??
Any chemical compound contains atoms and/or ions. Atoms are neutral (not charged), and any combination of atoms is neutral too. Ions are charged, but in any chemical compound the charges are compensated: total positive charge of all cations in a crystal exactly equals (by absolute value) to the total negative charge of all anions in a same crystal. Hence, the total electric charge of any portion of the chemical compound equals to zero. Since there is no charge, we don't mention it.