4.1 BONDING IN CARBON – THE COVALENT BOND · Part 2

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. Not just carbon, but many other elements form molecules by sharing electrons in this manner. The shared electrons ‘belong’ to the outermost shells of both the atoms and lead to both atoms attaining the noble gas configuration. Before going on to compounds of carbon, let us look at some simple molecules formed by the sharing of valence electrons. The simplest molecule formed in this manner is that of hydrogen. As you have learnt earlier, the atomic number of hydrogen is . 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, H . This allows each hydrogen atom to attain the Table . Melting points and boiling points of some compounds of carbon Compound Melting Boiling point (K) point (K) Acetic acid (CH COOH) Chloroform (CHCl ) Ethanol (CH CH OH) Methane (CH ) Figure . Figure . Figure . Figure . Figure . Triple bond between two nitrogen atoms Figure . Figure . Figure . Figure . Figure . Double bond between two oxygen atoms electronic configuration of the nearest noble gas, helium, which has two electrons in its K shell. We can depict this using dots or crosses to represent valence electrons (Fig. . ). 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, as shown in Fig. . . The atomic number of chlorine is . What would be its electronic configuration and its valency? Chlorine forms a diatomic molecule, Cl . Can you draw the electron dot structure for this molecule? Note that only the valence shell electrons need to be depicted. In the case of