For the sack of attaining the stability, atoms interact with other atoms to form chemical bond. Chemical bond is a region which forms because of interaction of electrons from different atom. The valence shell electrons of atoms participate in the formation of chemical bond. When two atoms approach each other, their valence electrons repel while they are attracted to the protons within atoms. These opposite forces between two atoms are responsible for the bond formation. There are various theories to explain the chemical bonds in different molecules like Kossel-Lewis approach, Valence Shell Electron Pair Repulsion (VSEPR) Theory, Valence Bond (VB) Theory and Molecular Orbital (MO) Theory.
Types of chemical bond
There are various type of chemical bonds depends upon the bonded atoms, their electronic configuration as well as the difference in electronegativity.
- Ionic bond: Formed between ions through complete transfer of electrons
- Covalent bond: Formed between atoms through equal sharing of electrons
- Coordinate bond: Formed between atoms through unequal sharing of electrons
- Metallic bond: Formed between metal ions and electrons.
- Van der wall force: Formed between atoms or molecule.
Out of these all types of bonds ionic and covalent bonds are most common in a large number of molecules.
1. Ionic bond
This type of bond formed by complete transfer of electrons form one atom to another. This complete transfer of electron creates cation (positively charged ion) and anion (Negatively charged ion). Because of opposite charges, these ions attract each other and this electrostatic force of attraction is termed as ionic bond. This type of bonds also termed as electrovalent bond and compound involve in such bonds are called as ionic compounds or electrovalent compounds.
Generally ionic bonds form between highly electropositive and highly electronegative atoms. Like metal (electropositive) and non-metal (electronegative) form ionic bond. For example, Calcium chloride molecule is an ionic compound which form through the formation of ionic bond between calcium ion and two chloride ion.
Ions in ionic compounds arranged in a certain order arrangement known as crystal lattice. Due to this order arrangement and strong electrostatic force of attraction, they show high melting point and boiling point as well as conductor nature.
2. Covalent bond
In place of complete transfer of electron in ionic bond, if there is sharing of electrons between two atoms (generally non-metals) to attain the noble gas configuration than it’s known as covalent bond.
For example, Chlorine atom has 1s2, 2s2, 2p6, 3s2,3p5 electronic configuration with seven elections in its valence shell. Hence for attaining the nearest noble gas configuration that is argon, it required one electron. For attaining the octet in its valence shell; each chlorine atom share its valence electron with other chlorine atom and form a covalent bond in chlorine molecule.
Hence a covalent bond formed due to the overlapping of atomic orbitals. The overlapping of atomic orbitals results the formation of molecular orbitals.
The overlapping of atomic orbitals can be two types.
- Overlapping along the axis results the formation of strong sigma bond.
- Overlapping by the side way form weak pi bonds.
Pi bond is weak due to the distribution of electrons above and below the plane compare to sigma bonds which distributed along one axis only. Hence, pi bond cannot exist alone and they always formed with sigma bond.
Carbon is located in 14th group of periodic table and first member of carbon family. Its atomic number is six with 1s2, 2s2, 2p2 electronic configuration. Hence there are four electrons in its valence shell. For attain the nearest noble gas configuration it required four electrons.
There are two possible ways to get noble gas configuration.
- Either loses four valence shell electron and convert in C4+ ion.
- Or accept four electrons and convert in C4- ion.
Both options are not favorable under normal conditions, hence carbon share its four electrons with other atoms and form four covalent carbon bonds.
- In other words carbon’s covalency is four and that is also called as tetravalency of carbon.
- Due to tetravalency of carbon atom, it can form with same or different atoms and form a large number of compounds.
- These compounds are called as organic compound. In any organic compound the number of carbon atoms can be one to thousands.
- All carbon atoms have a strong tendency to form covalent bond with another carbon atom.
Like this all carbon atoms can form a long chain, this property of carbon atom is known as catenation. On the basis of bonding of carbon atom with other carbon atom, they can four types.
Carbon Carbon Double Bond
When two pairs of electrons are shared between two carbon atoms, it formed carbon-carbon double covalent bond. A double covalent bond is combination of one sigma and one pi bond. The carbon-carbon double covalent bond is shown by two lines joining the bonding carbon atoms and each line represents one pair of shared electrons.
Hence, two valency of carbon is bonded with one carbon atom while rest of two valency are satisfied by same of different atom. Such hydrocarbons which contain carbon-carbon double bond are named as alkene. For example, ethene (H2C=CH2). There is one carbon – carbon double covalent bond and four single covalent bonds between carbon and hydrogen atoms in one ethene molecule.
Each carbon atom in ethene form sp2 hybridization with the use of one and two p orbital.
Rest of one 2p orbitals on each carbon remains unhybridized and involve in pi bond through the side way overlapping. The sp2 hybrid orbitals are arranged in trigonal planer geometry with 120° bond angle. Sigma bonding electrons are distributed along the axis while pi bonding electrons are distributed above and below the plane of sigma bond.
Carbon Triple Bond
Some Points about Carbon Triple Bond:-
- When carbon –carbon covalent bond involve three pair of electrons or six electrons, its termed as carbon-carbon triple bond.
- Carbon-carbon triple covalent bond represented by three straight lines between bonded atoms.
- For example ethyne molecule has one carbon-carbon triple bond with two carbon-hydrogen bond.
- Each carbon is sp hybridized in triple bond formation.
- Each sp hybridized orbital of carbon atom form sigma bond with another carbon atom and one hydrogen atom.
- While two unhybridized 2p orbitals formed pi bond through side way overlapping.
- The so hybrid orbitals are arranged in linear geometry and with 180o bond angle.
- The bond length of carbon-carbon triple bond is shorter than single and double covalent bonds with 1.09 Å of carbon – hydrogen bond length and 1.2 Ao C-C bond length.
- The bond angle is 180° with linear geometry.
The carbon-carbon bond can be identify by using certain parameters like
- Carbon-carbon bond length
- Carbon-carbon bond angle
- Carbon-carbon bond strength
- Carbon-carbon bond energy
Such carbon atoms bonded with one more carbon atom in organic compound. For example in ethane molecule, both carbon atoms are bonded with one more carbon atom, hence both are example of primary carbon atom.
These carbon atoms bonded with two more carbon atoms in an organic compound. For example, propane
(C3H8) two primary carbon atom which present at terminal and one secondary carbon atom located at center of molecule.
Those carbon atoms which bonded with three more carbon atoms are termed as tertiary carbon atoms. For example, 2-methylpropane contains one tertiary carbon atom.
Quaternary carbon bonded with four more carbon atoms. For example, 2,2-Dimethylpropane contains on carbon atom located at second position in parent chain bonded four methyl groups.
Because of tetravalency of carbon atom, it can form four bonds with same or different atoms or groups. A carbon can form three types of bonds.
- Carbon-Carbon Single covalent bond: Sigma bond
- Carbon-Carbon double covalent bond: One sigma bond + one pi bond
- Carbon-Carbon triple covalent bond: One sigma bond + two pi bond
Carbon-Carbon single bond
If the tetravalency of carbon atom is satisfied by four atoms, it results the formation of carbon-carbon single bond.
For example, In Methane (CH4) each carbon atom forms four sigma covalent bonds with four hydrogen atoms. All carbon-carbon single covalent bond formed by axial overlapping of sp3 hybridized orbitals of carbon atom. Four sp3 hybridized orbitals of carbon atom are arranged in tetrahedral manner with 109°28’ bond angle. Each hybridized orbital overlap with 1s orbital of hydrogen atom to form single covalent bond.
The equilibrium distance between the nuclei of two bonded carbon atoms in a molecule is called as bond length.
As the number of pi bond increases in carbon-carbon covalent bond, the bond length decreases. This is because of the presence of pi bond carbon atoms come closer to each other and bond length decreases.
Carbon-Carbon Bond Angle
The angle between the hybrid orbitals of central atom of a molecule which contains bonding electron pairs. The bond angle can be experimentally determined by spectroscopic methods and expressed in degree. Bond angle depends on the type of hybridization of carbon atom.
Bond angle helps in determination of shape of molecule. For example, the bond angle in methane is 109°28’.
Carbon-Carbon Bond Strength
The bond strength is measurement of the covalent bond between two carbon atoms. In other words, bond strength is directly linked with bond order and the degree to which each atom linked to another atom contributes to the valency of this other atom.
More the bond order more will be the bond strength. Bond order in the number of bonds between two bonded atoms. Bond strength can be estimated by using bond energy or bond dissociation energy.
The amount of energy involved in bond formation or bond cleavage is known as bond energy.
Carbon-Carbon Bond Energy
In other words, bond energy is an indirect measure of bond strength. As the bond strength increases due to the presence of pi bond, the bond energy also increases. As more energy required cleaving a strong bond compare to weak bond.
The bond energy of different covalent bonds in between carbon atoms is as follows.
Hence, as the number of bond increases, bond energy increases.
Hence, the increasing order of bond energy is Single < Double < Triple covalent bond
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