Chemical Bonding and Molecular Formula

Chemical Bonding

Chemical bonding is the force of attraction that binds atoms or group of atoms to form a stable chemical molecule or compound. For example, hydrochloric acid (HCL) is formed of one molecule of hydrogen and one molecule of chlorine. The chlorine and hydrogen are found combined together due chemical bond. There are various type of chemical bonding. Here we study about two types of bonding which are given below,

Electrovalent bond

The chemical bond formed by the transfer of electrons from valence shell of an atom to the valence shell of another atom is called electrovalent bond and the valency is known as electrovalency.

Electrovalent bond is formed in between two atoms in which one atom belongs to metal and another is non-metal. The metal atom loses its valence electron and gains positive ions or cation. On the other hand, non-metal atom gains an electron from metal to form stable negative ion or anion. Compounds like magnesium chloride, calcium oxide, sodium oxide, magnesium oxide and potassium chloride are formed by the electrovalent bonding.

Characteristics of electrovalent compounds

• They have high boiling point and melting point.
• Found in solid state
• Conduct electricity in molten or aqueous solution.
• Contains metal in their molecule.

Covalent bond

The covalent bond is formed by the sharing of a pair of electrons between two atoms each contributing an equal number of electrons to the electron pair. A covalent bond is represented by line (-) between the bonded atoms. When one pair of electron is shared, a single covalent bond is formed. Similarly, when two and three pairs of electrons are shared, they form double and triple bond respectively. Compounds like methane, ammonia, water and oxygen are formed by the covalent bonding.

Characteristics of covalent bond

• They have low melting point and boiling point.
• Do not conduct electricity.
• Water insoluble but soluble in organic solvents.
• Found in all three state i.e. solid, liquid and gaseous state.
• Do not contain metal.

Molecular Formula

A molecule is not a single atom but it is formed by the combination of two or more atoms of the same or different types in fixed proportion by their weight. Molecular formula is defined as the symbolic representation of the molecule of a substance. By observing the molecular formula, we can determine the no. of atoms involved in the formation of the molecule.

Molecular formula of an element: The molecular formula of an element is defined as the symbolic representation which shows the actual number of atoms in one molecule of the element.

Molecular formula of a compound: The molecular formula of a compound is defined as the symbolic representation which shows the actual number of an atom of different elements present in one molecule of the compound.

Information obtained from molecular formula

• It represents the composition of each element present in the given compound.
• It gives information about the total number of atoms of different elements involved in the formation of the molecule.
• It shows the combining capacity of its constituent elements with hydrogen i.e. valency.
• We can calculate molecular weight of the substance by observing its molecular formula.
• It represents one molecule of the substance.

Writing molecular formula:

To write the molecular formula of a molecule, we should follow the following steps given below,

Step 1: At first we should know the symbol and valences of elements and radicals present in a molecule.
Step 2: Write the name of the compounds
Step 3: Determine the basic and acidic charges
Step 4: Valency of one radical is transferred to another radical and is written on the right hand side at the bottom corner. If necessary, L.C.M. of the valencies is taken to get a simple whole number.
Step 4: When a compound radical is involved in molecular formula, the radical is enclosed in a bracket and the valency number is written on the right side of the bracket at the bottom of the formula.

For example; Calcium sulphate

1. Calcium Sulphate (compounds)
2. Ca SO₄ (symbol of basic and acidic radicals)
3. Ca² SO₄² (valency at right upper corners of the symbols)
4. Ca₂ (SO₄)₂ (valency are exchanged and compound radical is enclosed in bracket)
5. CaSO₄→ (L.C.M. is taken to get molecular formula of calcium sulphate)

Differences between symbol and molecular formula: