# Molecular Formula

## What is Molecular Formula?

Chemical formulas were first derived by determining the masses of all the elements that combine to create a molecule, leading to the development of two important types of chemistry formulae: molecular formula and empirical formula.

The molecular formula gives the exact number of every single atom present in a molecule, whereas the empirical formula gives the simplest ratio of the number of various atoms present. It is an empirical formula if the formula is simplified. The molecular formula is a multiple of the empirical formula and is often used.

### What is Molecular Formula Meaning?

The molecular formula is a formula generated from molecules that represents the total number of individual atoms in a compound's molecule. A subscript in a molecular formula indicates the number of each type of atom in a molecule of the substance.

Molecular formulas are linked to gram molecular masses, which are simple whole number multiples of the empirical formula mass.

### Relationship Between Empirical and Molecular Formula

The empirical formula is the simplest formula for a compound, defined as the ratio of subscripts of the smallest whole number of elements in the formula. It's also referred to as the most basic formula.

The formula of a substance expressed with the smallest integer subscript is called an empirical formula.

The empirical formula specifies the number of atoms in the compound in a given ratio. The empirical formula of a compound is directly proportional to its % composition.

### What is Meant by Molecular Formula?

Molecular Formula  = n × Empirical Formula

This equation shows the molecular formula definition chemistry.

### Solved Examples

Example 1: Caffeine has the following composition: 49.48% of carbon, 5.19% of hydrogen, 16.48% of oxygen and 28.85% of nitrogen. The molecular weight is 194.19 g/mol. Find out the molecular and empirical formula.

Solution:

Multiply percent composition with the molecular weight,

Carbon – 194.19 x 0.4948 = 96.0852

Hydrogen – 194.19 x 0.0519 = 10.07846

Oxygen –  194.19 x 0.1648 = 32.0025

Nitrogen – 194.19 x 0.2885 = 56.0238

Divide each value by the atomic weight,

Carbon : 96.0852 / 12.011 = 7.9997

Hydrogen : 10.07846 / 1.008 = 9.998

Oxygen : 32.0025 / 15.9994 = 2.000

Nitrogen : 56.0238 / 14.0067 = 3.9997

Round off the values to closest whole number,

8: Carbon

10: Hydrogen

2: Oxygen

4: Nitrogen

Hence, the molecular formula is C8H10N4O2.

As we know 2 is the common factor of 8, 10, 4 and 2.

The empirical formula is C4H5N2O.

Example 2: The empirical formula is BH3 of boron hydride. Calculate the molecular formula given the measured mass is 27.66.

Solution:

Atomic mass  = B + 3(H) = 10.81 + 3(1) = 13.81u

The measured molecular mass for an atom is given as 27.66u.

Molecular formula = n × empirical formula

n = molecular formula/empirical formula = 27.6613.81 = 2

Putting the value of n = 2 in the empirical formula,

Molecular formula = 2(BH3) = B2H6.

### Conclusion

The masses of all the elements combine to form a molecule. The empirical formula gives a ratio of the number of atoms present, but the molecular formula offers the exact number of every single atom present in a molecule. The total number of individual atoms in a compound's molecule is represented by the molecular formula.