- Melting points and boiling points of some compounds of carbon
- Allotropes of carbon
BONDING IN CARBON:-
Covalent bond is a chemical bonding process in which pairs of electrons are shared between two atoms. The force of attraction or repulsion between two atoms, when they share electron pair or bonding pairs, is called as Covalent Bonding. Carbon, having four electrons in its outer shell has given it the ability to form innumerable molecules and bonds. This is why carbon has so many elements and allotropes.
Most carbon compounds are poor conductors of electricity, these compounds have low melting and boiling points as compared to ionic compounds.
We can conclude that the forces of attraction between the molecules are not very strong. Since these compounds are largely non-conductors of electricity, we can conclude that the bonding in these compounds does not give rise to any ions.
electronic configuration of carbon: The atomic number of carbon is 6
Number of electrons in the K shell of carbon = 2
Number of electrons in the L shell of carbon = 4
The distribution of electrons in carbon can be written as = 2,4 ,
so carbon have 4 electrons in its valence shell (outer most shell ) .
Elements forming ionic compounds achieve this by either gaining or losing electrons from the outermost shell. 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. If it were to gain or lose electrons –
(i) It could gain four electrons forming C4– 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 C4+ 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. Now these shared atoms of the last shell, belong to both the atoms, hence forming a bond between these atoms. Now both atoms have a complete outer shell with eight atoms and have both attained noble gas configuration. This sharing of atoms, instead of gaining or losing is called covalent bonding.
The simplest molecule formed in this manner is that of hydrogen. the atomic number of hydrogen is 1. Hence hydrogen has one electron in its K shell and it requires one more electron to fill the K shell. So two hydrogen atoms share their electrons to form a molecule of hydrogen.
The shared pair of electrons is said to constitute a single covalent bond between the two hydrogen atoms. A single covalent bond is also represented by a line between the two atoms.
[H-H] Single bond between Hydrogen Atoms.
The atomic number of chlorine is 17.
Electronic configuration:- [ 2 - 8 - 7 ]
An atom of oxygen has six electrons in its 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.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.
O=O Double bond between Oxygen Atoms.
Formation of water molecule:
when hydrogen gas, H2(g), is burned in the presence of gaseous oxygen, O2(g), a new substance, liquid water, H2O(l) forms.
The covalent bonds within the H2 molecules and O2 molecules break,
and new covalent bonds form between oxygen atoms and hydrogen atoms.
What would happen in the case of a diatomic molecule of nitrogen? Nitrogen has the atomic number 7. What would be its electronic configuration and its combining capacity? 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. The electron dot structure of N2 and its triple bond can be depicted as
N≡N TRIPLE BOND BETWEEN NITROGEN ATOMS.
Allotropes of carbon
The element carbon occurs in different forms in nature with widely varying physical properties. Both diamond and graphite are formed by carbon atoms, the difference lies in the manner in which the carbon atoms are bonded to one another. In diamond, each carbon atom is bonded to four other carbon atoms forming a rigid three-dimensional structure. In graphite, each carbon atom is bonded to three other carbon atoms in the same plane giving a hexagonal array. One of these bonds is a double-bond, and thus the valency of carbon is satisfied. Graphite structure is formed by the hexagonal arrays being placed in layers one above the other.
These two different structures result in diamond and graphite having very different physical properties even though their chemical properties are the same. Diamond is the hardest substance known while graphite is smooth and slippery. Graphite is also a very good conductor of electricity.