BONDING IN CARBON – THE COVALENT BOND
`color{green}(★)` Reactivity of elements depends upon their tendency to attain a completely filled outer shell ( noble gas configuration).
`color{green}(★)` Elements forming ionic compounds achieve this by either gaining or losing electrons from the outermost shell.
`color{green}(★)` In the case of carbon, it has four electrons in its outermost shell and needs to gain or lose four electrons to attain noble gas configuration.
`color{green}(★)` If it were to gain or lose electrons –
(i) It could gain four electrons forming `color{red}(C^(4–))` anion. But it would be difficult for the nucleus with six protons to hold on to ten electrons, that is, four extra electrons.
(ii) It could lose four electrons forming `color{red}(C^(4+))` cation. But it would require a large amount of energy to remove four electrons leaving behind a carbon cation with six protons in its nucleus holding on to just two electrons. Carbon overcomes this problem by sharing its valence electrons with other atoms of carbon or with atoms of other elements. The shared electrons `color{red}("‘belong’")` to the outer shells of both the atoms and lead to both atoms attaining the noble gas configuration. Similarly other elements can attain stability by sharing of electrons.
For eg:
`color{green}(★)` The atomic number of hydrogen is 1. Hence hydrogen has one electron in its `color{red}(K)` shell and it requires one more electron to fill the `color{red}(K)` shell. So two hydrogen atoms share their electrons to form a molecule of hydrogen, `color{red}(H_2)`.
The shared pair of electrons is said to constitute a single bond between the two hydrogen atoms. A single bond is also represented by a line between the two atoms.
`color{green}(★)` The atomic number of chlorine is 17.
`color{green}(★)` In the case of oxygen there are six electrons in its `color{red}(L)` shell (the atomic number of oxygen is eight) and it requires two more electrons to complete its octet. So each atom of oxygen shares two electrons with another atom of oxygen to give us the structure shown in Fig. 4.3. The two electrons contributed by each oxygen atom give rise to two shared pairs of electrons. This is said to constitute a double bond between the two atoms.
`color{green}(★)` A molecule of water showing the nature of bonding between one oxygen atom and two hydrogen atoms.
`color{green}(★)` Nitrogen has the atomic number 7. In order to attain an octet, each nitrogen atom in a molecule of nitrogen contributes three electrons giving rise to three shared pairs of electrons. This is said to constitute a triple bond between the two atoms.
`color{green}(★)` The electron dot structure for `color{red}(NH_3)` molecule.
`color{green}(★)` METHANE:
1 A compound of carbon.
2 It is widely used as a fuel and is a major component of bio-gas and Compressed Natural Gas (CNG).
3 It is also one of the simplest compounds formed by carbon.
4 It has a formula `color{red}(CH_4)` .This is because hydrogen has a valency of 1 and Carbon is tetravalent because it has four valence electrons. Now in order to achieve noble gas configuration, carbon shares these electrons with four atoms of hydrogen.
So the bonds which are formed by the sharing of an electron pair between two atoms are known as covalent bonds.
`color{green}("𝐏𝐑𝐎𝐏𝐄𝐑𝐓𝐈𝐄𝐒 𝐎𝐅 𝐂𝐎𝐕𝐀𝐋𝐄𝐍𝐓 𝐁𝐎𝐍𝐃𝐒:")`
`color{green}(★)` Covalently bonded molecules are seen to have strong bonds within the molecule, but intermolecular forces are small.
`color{green}(★)` This gives rise to the low melting and boiling points of these compounds.
`color{green}(★)` Since the electrons are shared between atoms and no charged particles are formed, such covalent compounds are generally poor conductors of electricity.
`color{green}(★)` Elements forming ionic compounds achieve this by either gaining or losing electrons from the outermost shell.
`color{green}(★)` In the case of carbon, it has four electrons in its outermost shell and needs to gain or lose four electrons to attain noble gas configuration.
`color{green}(★)` If it were to gain or lose electrons –
(i) It could gain four electrons forming `color{red}(C^(4–))` anion. But it would be difficult for the nucleus with six protons to hold on to ten electrons, that is, four extra electrons.
(ii) It could lose four electrons forming `color{red}(C^(4+))` cation. But it would require a large amount of energy to remove four electrons leaving behind a carbon cation with six protons in its nucleus holding on to just two electrons. Carbon overcomes this problem by sharing its valence electrons with other atoms of carbon or with atoms of other elements. The shared electrons `color{red}("‘belong’")` to the outer shells of both the atoms and lead to both atoms attaining the noble gas configuration. Similarly other elements can attain stability by sharing of electrons.
For eg:
`color{green}(★)` The atomic number of hydrogen is 1. Hence hydrogen has one electron in its `color{red}(K)` shell and it requires one more electron to fill the `color{red}(K)` shell. So two hydrogen atoms share their electrons to form a molecule of hydrogen, `color{red}(H_2)`.
The shared pair of electrons is said to constitute a single bond between the two hydrogen atoms. A single bond is also represented by a line between the two atoms.
`color{green}(★)` The atomic number of chlorine is 17.
`color{green}(★)` In the case of oxygen there are six electrons in its `color{red}(L)` shell (the atomic number of oxygen is eight) and it requires two more electrons to complete its octet. So each atom of oxygen shares two electrons with another atom of oxygen to give us the structure shown in Fig. 4.3. The two electrons contributed by each oxygen atom give rise to two shared pairs of electrons. This is said to constitute a double bond between the two atoms.
`color{green}(★)` A molecule of water showing the nature of bonding between one oxygen atom and two hydrogen atoms.
`color{green}(★)` Nitrogen has the atomic number 7. In order to attain an octet, each nitrogen atom in a molecule of nitrogen contributes three electrons giving rise to three shared pairs of electrons. This is said to constitute a triple bond between the two atoms.
`color{green}(★)` The electron dot structure for `color{red}(NH_3)` molecule.
`color{green}(★)` METHANE:
1 A compound of carbon.
2 It is widely used as a fuel and is a major component of bio-gas and Compressed Natural Gas (CNG).
3 It is also one of the simplest compounds formed by carbon.
4 It has a formula `color{red}(CH_4)` .This is because hydrogen has a valency of 1 and Carbon is tetravalent because it has four valence electrons. Now in order to achieve noble gas configuration, carbon shares these electrons with four atoms of hydrogen.
So the bonds which are formed by the sharing of an electron pair between two atoms are known as covalent bonds.
`color{green}("𝐏𝐑𝐎𝐏𝐄𝐑𝐓𝐈𝐄𝐒 𝐎𝐅 𝐂𝐎𝐕𝐀𝐋𝐄𝐍𝐓 𝐁𝐎𝐍𝐃𝐒:")`
`color{green}(★)` Covalently bonded molecules are seen to have strong bonds within the molecule, but intermolecular forces are small.
`color{green}(★)` This gives rise to the low melting and boiling points of these compounds.
`color{green}(★)` Since the electrons are shared between atoms and no charged particles are formed, such covalent compounds are generally poor conductors of electricity.
