Chapter # 05 [Chemical Bonding]

 

UNIT# 05

CHEMICAL BONDING

Chemicals react with each other to get neutral. It is also a point to remember that only those elements react or tends to react with other elements which need to complete their valence shell. For the completion of the valence shell, atom undergoes in chemical reaction. In this way, a series of reactions occurs this was also explained by Isaac Newton that “Everybody in this universe attracts other body”

 

Q#	Questions	Year
Q# 01	What is chemical bond?	[2016][2015][2014] [2012][2007][2005]
Q# 02	Describe four characteristics of covalent compounds.	[2015] [2012] [2009]
Q# 03	Describe the formation of ionic bond.	[2013][2011][2007] [2005]
Q# 04	Describe the characteristics properties of ionic compounds.	[2017][2012]
Q# 05	Differentiate between ionic bond and covalent bond.	[2016][2011]
Q# 06	Differentiate between Covalent bond and coordinate covalent bond.	[2016][2013][2012] [2008][2006]
Q# 07	Define dispersion of forces.	[2009][2006]
Q# 08	Write note on Metallic bond.	[2016][2006]
Q# 09	Write note on Hydrogen bond.	[2016][2009]
Q# 10	What is an ion? Write the electronic configuration of sodium ion and chloride ion. What is an Ionic compound? Write chemical formula of sodium chloride.
Q# 11	What is coordinate covalent bond? How is coordinate covalent bond formed between NH3 and H+ ion?	[2011][2009] [2007]
Q# 12	Define Polar bond.	[2018]
Q# 13	Define ionic bond.	[2015][2006][2005]
Q# 14	Define non polar covalent bond.	[2012]
Q# 15	Define Vander wall’s forces.	[2006]
Q# 16	Define Dipole dipole forces.	[2006]
Q# 17	Define Covalent bond.	[2015] [2012]
Q# 18	Define coordinate covalent bond.	[2015]

 

Q. What is chemical bond? Name types of chemical bond.

CHEMICAL BOND AND ITS TYPES

CHEMICAL BOND

The force which holds the atoms together in a molecule is called chemical bond.

 

TYPES OF CHEMICAL BOND

Following are the types of chemical bond

1.      Ionic bond

2.      Covalent bond

 

Q. What is ionic bond? Explain the formation of ionic bond by giving example of formation of NaCl.

IONIC BOND

The bond formed by the complete transfer of electrons from one atom to another is called ionic bond.

OR

The attraction that binds the oppositely charged ions together is termed as ionic bond.

 

EXPLANATION

The attraction which attracts the Na ­⁺ and Cl^- atoms together is called ionic bond and the compound (NaCl) is called ionic compound.

 

In (NaCl) formation, the Na (sodium) which contains 1 electron in outermost shell  loses its electron and become Na⁺ atom while the Cl atom; having 7 electrons in outermost shell, need one electron to fulfil its orbit, accepts one electron from sodium atom and become Cl^-.

The reaction can be illustrated as:

Na       →        Na + e^-

Cl + e^-             →        Cl

Na⁺   +  Cl^‑     →        NaCl

Q. What are the characteristics of ionic compounds?

CHARACTERISTICS OF IONIC COMPOUNDS

1.      They are crystalline solid at room temperature.

2.      They have high melting point and boiling point.

3.      They do not conduct electricity.

4.      They are soluble in water.

5.      They are nonvolatile.

 

 

Q. What is covalent bond? Describe the formation of MgO.

COVALENT BOND

The bond which forms by the complete transfer of electrons is called covalent compound.

OR

The shared pair of electrons which links the atom in a molecule is known as covalent bond.

 

EXPLANATION

Let us consider the example of bond formation of methane. Carbon which requires 4e^- to complete its valence shell makes association with 4 Hydrogen atoms.

C + 4H            →        CH₄

 

FORMATION OF MgO

In MgO bond formation, Mg has two electrons in valence shell while oxygen requires two electrons to complete its octet. To accomplish the complete valence shell Mg loses its two electrons which received by oxygen. In this way, both atoms (Mg and O) acquire 8e^- in valence shell.

Mg                  →        Mg⁺² + 2e^-

O + 2e^-           →        O^-2

Mg⁺² + O^-2     →        MgO

 

Q. Describe types of covalent bond.

TYPES OF COVALENT BOND

Following are the types of covalent bond.

        I.            Single covalent bond

     II.            Double covalent bond

   III.            Triple covalent bond

 

SINGLE COVALENT BOND

In single covalent bond the only single pair of electrons is shared by the bonded atoms, in which each atom has to share one electron.

It represents by single short line (-).

FOR EXAMPLE

·        HCl [H-Cl]

·        H₂ [H-H]

·        F₂ [F-F]

·        Cl₂ [Cl-Cl]

·        Br₂ [Br-Br]

 

DOUBLE COVALENT BOND

In double covalent bond, only two pairs of electron are shared by the bonded atoms, in which each atom has to share two unpaired electrons.

It represents by two short lines (=)

FOR EXAMPLE

·        CO₂ [O=C=O]

·        O₂ [O=O]

·        C₂H₄ [H₂C=CH₂]

 

TRIPLE COVALENT BOND

In triple covalent bond, three pairs of electrons are shared by the bonded atoms and each atom has to share three unpaired electrons.

It represents by (Ξ)

FOR EXAMPLE

·        N₂ [NΞN]

·        CN

·        C₂H₂ [HC Ξ CH]

 

Q. Give the characteristics of covalent compounds.

CHARACTERISITCS OF COVALENT COMPOUND

1.      They are insulators.

2.      They are insoluble in polar solvents like water but soluble in non-polar solvents like benzene.

3.      They have low melting and boiling point.

4.      Compounds have weak inter molecular forces.

5.      They are volatile.

6.      They are non-electrolytes.

 

Q. Describe polar and non-polar covalent bond.

POLAR COVALENT BOND

When the difference in electro negativities of bonded atoms is up to 1.7 than the bond is called Polar Covalent Bond.

OR
covalent bond forms by the mutual and unequal sharing of electron between different atoms of nonmetals which have different electro negativities is called Polar covalent bond.

FOR EXAMPLE

HCl, NH₃

 

NON-POLAR COVALENT BOND

If the difference in electro negativities of the bonded atoms is zero than the bond is called Non-polar covalent bond.

OR

The bond which is formed by the mutual and equal sharing of electron between the same atoms of nonmetals is called non polar covalent bond.

FOR EXAMPLE
H₂, N₂

 

Q. Distinguish between Ionic bond and covalent bond.

 

S#	Ionic bond	Covalent bond
1	It is formed by the transfer of electron from one atom to another	It is formed by the sharing of electrons
2	Electrostatic	Non electrostatic
3	Ionic substances are formed by the ionic bond	Molecules are formed by the covalent bond
4	Ionic bind has non directional character	Covalent bond has Directional character
5	It is always polar	It may be polar or non-polar
6	No multiplicity is observed	Bond may be single, double or triple bond

 

Q. Distinguish between Covalent bond and coordinate covalent bond.

S#	Covalent Bond	Coordinate covalent bond
1	It is formed by the mutual sharing of electrons	It is formed  by the one sided sharing of electron pair
2	It may formed between similar or dissimilar atom	It forms between two unlike atoms
3	It may be polar or non-polar	It is always polar
4	Compound are usually insoluble in water	Compounds are sparingly soluble in water

 

Q. Define Coordinate covalent bond. Describe the formation of ammonium chloride and water.

CO-ORDINATE COVALENT BOND

The bond which is formed by the one sided sharing of lone pair of electron is called coordinate covalent bond.

 

In this type of bonding, both electrons forming a bond are supplied by one atom only.

Donor the atom which supplies the pair of electron for bond formation is known as Donor.

Acceptor the atom which receives the pair of electron for bond formation is known as Acceptor.

Coordinate covalent bond denotes by arrow (⟶).

 

EXAMPLE OF AMMONIUM CHLORIDE

In the formation of ammonium chloride by the union of ammonia (NH₃) and hydrogen chloride (HCl) molecule, the nitrogen (N) atom of ammonia acts as the donor of the electron pair and hydrogen ions (H⁺) of hydrogen chloride accept it and form NH₄Cl

 

REACTION

NH₃ + HCl    →         NH₄Cl 

 

EXAMPLE OF WATER

Let us consider another example of coordinate covalent bond which is H₂O. Oxygen atom in water molecule has a lone pair of e^-, so the hydrogen atom forms an acid by combing with it and results in the formation of oxonium ion or hydronium ion (H₃O⁺).

H₂O + H⁺        ⟶       H₃O⁺

 

Q. Write note on Metallic bond.

METALLIC BONDING

The combination of electrostatic attraction between the electrons and the positive nuclei of atoms is called metallic bond.

 

PROPERTIES

1.      They are good conductor of heat.

2.      They are malleable.

3.      They are ductile in nature.

 

Q. Write note on Hydrogen bond.

HYDROGEN BONDING

Hydrogen bonding is the force of attraction between two polar molecules containing a hydrogen atom covalently bonded to an atom of F, O or N.

Best example is water.

It has strong type of dipole-dipole attraction.

Hydrogen bond is denoted by dotted lines (. . .)

FOR EXAMPLE

·        HF

·        HCl

·        H₂O

Q. Write note on Vander Waals forces.

VAN-DER WAALS FORCES

Van der Waals forces' is a common term which is used to define the attraction of intermolecular forces between molecules. There are two different kinds of Van der Waals forces

·        Weak London Dispersion Forces and

·        Stronger dipole-dipole forces.

 

WEAK LONDON DISPERSION FORCES

The London dispersion forces are one of the weakest intermolecular forces. These are the temporary attractive forces which results when the electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles. These forces are occasionally called an induced dipole-induced dipole attraction.

 

STRONG DIPOLE-DIPOLE FORCES

Dipole-dipole forces are the attractive forces between the positive and the negative end of another polar molecule. Dipole-dipole forces have strengths that range from 5 KJ to 20 KJ per mol