Halogens are more electronegative than carbon. Thus halogen atoms have a greater tendency than carbon atoms to attract electron density. So the nature of C-X bonds between halogen and carbon is polar in nature.
Nature of C-X bonds
Any general halogen is denoted by symbol X. So, C-X bond denotes the bond between carbon and halogen. Halogens are 17th group elements of the modern periodic table. They are short of one electron from completing their nearest noble gas configuration. The 17th group elements, in increasing order of their atomic sizes, are arranged in the modern periodic table as follows:
Carbon is in 14th group and as we know that the electronegativity of elements decreases across a period in the modern periodic table, hence halogens are more electronegative than carbon. This characteristic of halogens as compared to carbon can be attributed to the small size of halogen atoms.
Features of C-X bonds
The various features of a C-X bond are mentioned below.
- Since halogens are more electronegative than carbon, the carbon-halogen bond is polarized. Due to the high electronegativity of halogens, they attract the shared pair of electrons more towards themselves and thus halogens gain a slightly negative charge and carbon gets a slight positive charge.
- Only single bonds are formed between one carbon and one halogen atom as halogens need only 1 electron to complete their nearest noble gas configuration, while carbon needs 4 electrons to complete its nearest noble gas configuration. Hence after the bond formation between C and X, halogen atom completes its octet but carbon still needs 3 more electrons to complete its octet.
- As the size of halogens increases from fluorine to astatine, the C-X bond length increases and bond dissociation strength decreases.
- We know that electronegativity decreases down the group, hence dipole moment which depends on the difference in electronegativity of carbon and halogen also decreases down the group. The only exception in group 17 is that the dipole moment of the C-Cl bond is more than C-F; everything else follows the normal trend.
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