Note on Chemical Bonding and Molecular Formula

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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:

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.

  • 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.
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Very Short Questions

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.

0%
  • The numbers of electrons lost gained or sharing by an atom in the formation of a chemical bond is called

    Valency
    Electrovalency
    Ions
    Chemical bond
  • The force that is responsible to hold the atoms in a molecule is called

    Electrovalent bond
    Chemical bond
    Shell force
    Covalent bond
  • The compounds which are formed as a result of electrovalent bonding are called

    Covalent compounds
    Chemical compounds
    Divalent compounds
    Electrovalent compounds
  • In which state are electrovalent compounds found?

    Gas state
    Solid state
    Liquid state
    Viscous form
  • The electrovalent compounds have

    High melting and low boiling point
    Low boiling and high melting point
    Low melting and boiling point
    High boiling and melting point
  • The chemical bond that is formed by the mutual sharing of electrons between two or more non- metal atoms are called

    Ionic bond
    Electrovalent bond
    Covalent bond
    Electronic bond
  • The chemical compounds which are formed by covalent bonding are called

    Covalent compounds
    Valence compounds
    Ionic compounds
    Electrovalent compounds
  • The symbolic representation of a molecule is known as

    Symbol
    Molecular formula
    Short molecule
    Molecule identification
  • In which states are covalent compound formed?

    Gas
    All of the given
    Liquid
    Solid
  • What is the valency of Magnesium?

    3
    2
    1
    5
  • What is the valency of Aluminium?

    0
    2
    1
    3
  • What is the valency of Sulphur?

    0
    3
    1
    2
  • What is the molecular weight of Carbon dioxide?

    33 amu
    56 amu
    20 amu
    44 amu
  • What is the molecular weight of oxygen?

    32 amu
    44amu
    18 amu
    20 amu
  • What is the valency of oxygen in water?

    2
    0
    3
    1
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Bebek Paudel

Draw the molecule of calcium chloride


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