Covalent bond:
A chemical bond formed by the sharing of one or more electrons, especially pairs of electrons, between atoms. Usually each atom contributes one electron to form a pair of electrons that are shared by both atoms, for gain more stability.
Non metal are readily form
covalent bond with other non metals for gain stability. Covalent bond shows less melting point and
more boiling point ,and there are less soluble in water. Bond energy is also
more ,when compared to other bonds. Energy is releasing from bond formation is more than the energy
require for bond break down so generally covalent bonds are exothermic.
To understand how sharing a pair of electrons can hold atoms
together, let's look at the simplest covalent bond the bond that forms
when two isolated hydrogen atoms come together to form an H2
molecule.
When a pair of isolated hydrogen atoms are brought together,
two new forces of attraction appear because of the attraction
between the electron on one atom and the proton on the other.
At the same time two forces of repulsion also observed ,electrons of one atom and electrons of the other atom ,same thing in positively charged protons of one atom and positively charged protons of other atom .
It might seem that the two new repulsive forces would balance the two new attractive forces. But there are ways in which the forces of repulsion can be minimized. As we have seen, electrons behave as if they were tops spinning on an axis. There are two possible states for the spin of an electron: s = +1/2 and s = -1/2 .at magnetic field. When electrons are paired so that they have opposite spins, the force of repulsion between these electrons is minimized.
The force of repulsion between the protons can be minimized by placing the pair of electrons between the two nuclei. The distance between the electron on one atom and the nucleus of the other is now smaller than the distance between the two nuclei(electrons present in between two nuclei, ). As a result, the force of attraction between each electron and the nucleus of the other atom is larger than the force of repulsion between the two nuclei, as long as the nuclei are not brought too close together.
The net result of pairing the electrons and placing them between the two nuclei is a system that is more stable than a pair of isolated atoms if the nuclei are close enough together to share the pair of electrons, but not so close that repulsion between the nuclei becomes too large.
Depend up on atoms electronegative covalent bond are divided in to two
Depends up on number of electron sharing covalent bond divided into 3 types:
single bond:
two atoms shares one pair of electrons,
single bond is called a sigma bond and it consists of the end-to-end overlap of hybrid orbitals. Single bonds between are longest and weakest.Example
H-O-H,
Double bond:
A double bond is a sigma bond plus a pi bond. A pi bond is the side-to-side overlap of unhybridized p-orbitals. A double bond between the same two elements is shorter and stronger.
O=C=O
Triple bond:
A triple bond is a sigma bond plus two pi bonds. A triple bond between he same two elements is shortest and strongest.
How sharing of electrons bond atoms
H � + � H 
H-H
An isolated hydrogen atom contains one proton and one electron
held together by the force of attraction between oppositely
charged particles. The magnitude of this force is equal to the
product of the charge on the electron (qe)
times the charge on the proton (qp)
divided by the square of the distance between these particles (r2).
H-HAt the same time two forces of repulsion also observed ,electrons of one atom and electrons of the other atom ,same thing in positively charged protons of one atom and positively charged protons of other atom .
It might seem that the two new repulsive forces would balance the two new attractive forces. But there are ways in which the forces of repulsion can be minimized. As we have seen, electrons behave as if they were tops spinning on an axis. There are two possible states for the spin of an electron: s = +1/2 and s = -1/2 .at magnetic field. When electrons are paired so that they have opposite spins, the force of repulsion between these electrons is minimized.
The force of repulsion between the protons can be minimized by placing the pair of electrons between the two nuclei. The distance between the electron on one atom and the nucleus of the other is now smaller than the distance between the two nuclei(electrons present in between two nuclei, ). As a result, the force of attraction between each electron and the nucleus of the other atom is larger than the force of repulsion between the two nuclei, as long as the nuclei are not brought too close together.
The net result of pairing the electrons and placing them between the two nuclei is a system that is more stable than a pair of isolated atoms if the nuclei are close enough together to share the pair of electrons, but not so close that repulsion between the nuclei becomes too large.
Depend up on atoms electronegative covalent bond are divided in to two
Polar and non polar covalent
bonds.
Electronegative: how strongly an atom will attract electrons to itself when bonded to another element. In periodic table electronegativity increase from left to right ,non metals ,atoms which are close to Florine atom and atoms with less atomic radius( in periodic table atomic radii decrease from left to right) also show more electronegativity.
The difference between two atoms electronegativity is less than 1.65 , covalent bond . if difference more than 1.65 that is ionic bond
Electronegative: how strongly an atom will attract electrons to itself when bonded to another element. In periodic table electronegativity increase from left to right ,non metals ,atoms which are close to Florine atom and atoms with less atomic radius( in periodic table atomic radii decrease from left to right) also show more electronegativity.
The difference between two atoms electronegativity is less than 1.65 , covalent bond . if difference more than 1.65 that is ionic bond
Polar covalent bond: Formation of a covalent bond between two atoms which belong to
different element is known as a polar covalent bond. The
bonding pair of electrons will lie more towards the atoms which have
higher electronegative . As the said electron pair do not lie exactly midway
between the two atoms. The atom having higher affinity for electrons
gets a slightly negative charge and the atom with lesser affinity for
electrons develops a slightly positive charge. Such molecules are called
‘polar molecules’.
For example: H-Cl,H-O-H
Hydrogen chloride (HCl) molecule forms polar covalent bond. The bonding of hydrogen and chlorine atoms lies more towards Cl atom (because Cl is more electronegative) in the shared pair of electrons. Therefore, Cl atom acquires a slight negative charge, and H atom a slight positive charge.
Non-polar covalent bond
During the Formation of a covalent bond between two atoms which belong to the same electronegative elements, the pair which is shared will lie in the middle of the two atoms. This means the atoms involved in sharing will share the electrons equally. Hence molecule obtained will be electrically symmetrical. Electrically symmetrical means center of the positive charge coincides with the center of the negative charge. This type of covalent bond formed is known as a non-polar covalent bond.
For example: The bonds in the molecules H2, O2, Cl2 etc., are non-polar covalent bonds.
H• + x H ———> H x H
: Ö: +: Ö: ———–> : Ö: Ö:
For example: H-Cl,H-O-H
Hydrogen chloride (HCl) molecule forms polar covalent bond. The bonding of hydrogen and chlorine atoms lies more towards Cl atom (because Cl is more electronegative) in the shared pair of electrons. Therefore, Cl atom acquires a slight negative charge, and H atom a slight positive charge.
Non-polar covalent bond
During the Formation of a covalent bond between two atoms which belong to the same electronegative elements, the pair which is shared will lie in the middle of the two atoms. This means the atoms involved in sharing will share the electrons equally. Hence molecule obtained will be electrically symmetrical. Electrically symmetrical means center of the positive charge coincides with the center of the negative charge. This type of covalent bond formed is known as a non-polar covalent bond.
For example: The bonds in the molecules H2, O2, Cl2 etc., are non-polar covalent bonds.
H• + x H ———> H x H
: Ö: +: Ö: ———–> : Ö: Ö:
Depends up on number of electron sharing covalent bond divided into 3 types:
single bond:
two atoms shares one pair of electrons,
single bond is called a sigma bond and it consists of the end-to-end overlap of hybrid orbitals. Single bonds between are longest and weakest.Example
H-O-H,
Double bond:
A double bond is a sigma bond plus a pi bond. A pi bond is the side-to-side overlap of unhybridized p-orbitals. A double bond between the same two elements is shorter and stronger.
O=C=O
Triple bond:
A triple bond is a sigma bond plus two pi bonds. A triple bond between he same two elements is shortest and strongest.
Covalent structures: They are three types of covalent structures are present , individual molecules, molecular structures, and macromolecular structure.
individual molecules: strong bond between atoms but negligible bond between molecules.All gases are come to this type of covalent structures. all gases come to this structure for example, HCl, SO2, CO2, and CH4.
Molecular structures: there are weak forces of attraction. Such covalent substances are low-boiling-temperature liquids and low melting points
Macromolecular structure :Macromolecular structures have large numbers of atoms linked in chains or sheets example Graphite ,in 3-dimensional structures (such as diamond and quarts) . These substances have high melting and boiling points, are frequently brittle, and tend to have high electrical resistivity .l Eements that have high electronegativity and the ability to form three or four electron pair bonds, often form such large macromolecular structures.
