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Chemical Formula of Common Compounds

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An atom is the smallest unit of an element capable of participating in a chemical reaction. A molecule is an electrically neutral group of two or more atoms. The composition of a molecule of a substance is represented by a chemical formula in terms of the symbols representing the elements contained in the molecule. The chemical formulae, the formation of elements and the formation of compounds are defined below.

What is a Chemical Formula?

A chemical formula is a representation of a substance’s molecular composition in terms of the symbols representing the components that make up the molecule. A molecular formula is another name for a chemical formula. 

An element’s or a compound’s chemical formula can be used. A chemical formula is a technique of presenting information on the chemical proportions of atoms that make up a chemical compound or molecule using chemical element symbols, numbers, and other symbols like parentheses, dashes, brackets, and commas.

Formulae of Elements

The chemical formula of an element is a description of the molecule’s composition, with the symbol indicating the element and the subscript indicating the number of atoms in one molecule. 

Since one molecule of hydrogen contains two hydrogen atoms, the formula for hydrogen is H2. One molecule of hydrogen element includes two hydrogen atoms, according to the formula H2. Also, 2H denotes two separate hydrogen atoms, H2 denotes one hydrogen molecule, and 2H2 denotes two hydrogen molecules. 

Similarly, oxygen’s molecular formula is O2, nitrogen’s molecular formula is N2, and chlorine’s molecular formula is Cl2. Since inert gases like helium, none, and argon are monoatomic, they have the same symbols. There are no unique equations for the metals; they are all represented by their symbols.

The following table lists the molecular formulas for some of the most common elements:

















Formulae of Compounds

The chemical formula of a compound represents the elements present in the substance’s molecule in terms of their symbols. In other words, the formula of a compound tells us “the kind of atoms” present in one molecule of the compound, as well as the number of atoms of various elements present. 

A compound’s chemical formula is a description of its composition in which the chemical symbols indicate which elements are present and the subscripts indicate how many atoms of each element are present in one molecule. A compound’s chemical formula is a symbolic representation of the compound’s chemical composition. A chemical formula gives information about the elements that make up a compound’s molecules, as well as the ratio in which these elements’ atoms combine to form those molecules. 

Chemical formulae provide insight and distinction into a compound’s chemical composition. They also show the proportions in which the various constituents combine to generate the desired combination. While representing a compound in a chemical equation, its chemical formula is important. Ions, free radicals, and other chemical species can all be represented using chemical formulas. Most elements have only their chemical symbol as their formula. In balanced chemical equations, a chemical formula is used to represent an element or compound.

The chemical formulas and elements found in several common molecular compounds are listed below.



Elements present

Carbon dioxide


C and O



H and O

Sulphur dioxide


S and O



N and H

Hydrogen chloride


H and Cl



C and H



C, H, and O

Hydrogen sulphide


H and S

The formula of Water

Water is a compound with two hydrogen atoms and one oxygen atom in each molecule. As a result, the water formula is H2O. The symbol H in the formula H2O stands for two hydrogen atoms, not a molecule of hydrogen, while O stands for one oxygen atom. 2H2O, for example, indicates two water molecules. The 2 multiplies the entire H2O formula rather than just the first element. That is, 2H2O is made up of four hydrogen atoms and two oxygen atoms.

Importance of formulae of compounds

  • The compound’s name is represented by a formula.
  • The names of all the elements in the molecule are given in formulae.
  • The number of atoms of each element contained in a molecule is given by formulae.
  • One molecule of a compound is represented by a formula.
  • Formulae denote a definite mass of a substance.

Solved Question

Question 1: What is the difference between O2 and 2O?


O2 indicates that one molecule of oxygen element contains 2 atoms of oxygen and 2O indicates two separate atoms of oxygen.

Question 2: What is the importance of the formula H2O of water?


The formula tells us that water has two elements, hydrogen, and oxygen. It also tells us that one molecule of water comprises of two hydrogen atoms and one oxygen atom.

Question 3: In nature, what forms does oxygen gas take?


In a free atmosphere, oxygen exists in a diatomic form, i.e, O2

Question 4: In the formula HNO3, what do the symbols, H, N, and O3 mean?


The above compound is HNO3. According to the chemical formula of HNO3, H denotes one atom of hydrogen, N denotes one atom of nitrogen and O3 denotes three atoms of oxygen.

Question 5: In nature, what form do noble gases take?


The configuration of noble gases is stable, thus they do not need to combine with other atoms. As a result, noble gases such as He, Li, and others exist in nature as single atoms.

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Last Updated : 29 Oct, 2021
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