Chemical Bonding and Molecular Formula

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Overview

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.

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.

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

Molecular Formula

  • Molecular formula of an element
  • Molecular formula of a compound

 

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.

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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:

Symbol Molecular formula
It is an abbreviation of the full name of an element. It is the symbolic representation of a molecule.
It represents one atom of an element. It represents one molecule of an element or compound.
It is written according to the English,Latin or other names of an element.

Example: The symbol of hydrogen is H.

It is written with the help of symbols and valency of elements.

Example: Molecular formula of hydrogen is H2.

Things to remember
  • Molecular formula is defined as the symbolic representation of the molecule of a substance.
  • The chemical bond formed by the transfer of electrons from valence shell of an atom to valence shell of another atom is called electrovalent bond.
  • It includes every relationship which established among the people.
  • There can be more than one community in a society. Community smaller than society.
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  • common interests and common objectives are not necessary for society.
Videos for Chemical Bonding and Molecular Formula
Covalent and Ionic Chemical Bonding - Mr. Causey's Chemistry
Questions and Answers
The force of attraction by which atoms or group of atoms are combined together to form a stable chemical molecule or compound is called chemical bond.
The compounds which are formed as a result of electrovalent bonding are called electrovalent compounds.
The chemical compounds which are formed by covalent bonding are called covalent compounds.
The symbolic representation of molecule is called molecular formula.
The chemical bond formed by the transfer of electrons from the valence shell of one atom to the outermost shell of another atom is called electrovalent bond.
The covalent bond is defined as the chemical bond that is formed by the mutual sharing of electrons between two or more non- metal atoms.
The molecular weight is defined as the sum of atomic weight of all atoms of the molecule.
The molecular weight of oxygen is 32 amu.
The molecular weight of carbon dioxide is 44 amu.
Molecular formula tells about the number of atoms of each element present in one molecule of the compound.

Any four differences between ionic compounds and covalent compounds are given below table,

Ionic compounds Covalent compounds
Ionic compounds are mainly solids. Covalent compounds may be gases, liquids or solids.
They consistof ions. They consist of molecules.
They have high melting point and boiling point. They have generally low melting point and boiling points.
They conduct electricity in solution.
Eg: NaCl, CaSO4
They do not conduct electricity in solution.
Eg: H2O, CH4.

Potassium is a metal and chlorine is a non- metal. Potassium loses one electron and becomes positively charged and chlorine gains one electron and becomes negatively charged. So, potassium chloride is called ionic compound or electrovalent compound.

In the valence shell of an Argon, there are Eight electrons. That means it is stable by octate rule. That's why it neither gains electrons nor loose electron. So it has zero valency.

Any three information obtained from molecular formula are as follows,

  • It represents the percentage of composition of each element present in the given compound.
  • It represents one molecule of the substance
  • It helps to know aboutthe molecular weight of the substance.

Any three characteristics of covalent compound are as follows,

  • They do not conduct electricity.
  • They are insoluble in water but soluble in organic solvents.
  • They do not contain metal in them.
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