Empirical formula and molecular formula are the two ways of writing chemical formula. Empirical formula is generally used for ionic and covalent compounds. Molecular formula is generally used for covalent compounds. Ionic compounds are those which are formed by giving and receiving of electrons of two different elements such as sodium chloride or NaCl. Covalent compounds are formed by sharing of electrons such as CH4.

Empirical formula represents the smallest ratio with actual ratio by atoms. Cation or positively charges ions and anion or negatively charges ions plays an important role in the construction of empirical formula. After fulfilling the valence requirements of cations and anions of each atom, empirical formula can be determined. Carbon atoms come first in carbon compounds such as CHCl3 or chloroform.

Molecular formula represents the real number of atoms available in one molecule of that compound. Sometimes, molecular and empirical formula found to be same such as in H2o, NH3 and CH4. Molecular formula determines the molecular weight and structure of a molecule. But it is not true for organic compounds because only a part of molecule takes part in the chemical reaction. For organic compounds, structural formula have used. Structural formula made up of the real number of atoms present in the compound and the number of chemical bonds between them. It also involves length of chemical bonds and angle between them. Lewis dot form, bond-line, stick bond notation, valence orbital notation, and projection form are some of the illustration of structural formulae.

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