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eA SS Ish SCIENCELICHEMIStTRap ss, , 4.6. FUNCTION ee StRYGS), Sa AL GROUPS — wit; YOU BE MY FRIEND ?, we have disc, isla vory Méhdiy Gee only hydrocarbons, i.€., Compounds of carbon and hydrogen only. By, Cathy, nitORGh. cut ao e eae because it also forms bonds with other elements such as halogens, Siysen, nan oR : ca care These elements may replace one or more hydrogens of a hydrocarbon, a e 1 pais f, compounds are formed. In these a of carbon remains satisfied. As a result of this replacement, new, , chain is referred ere compounds, the element replacing hydrogens of the parent hyd, , ; S, ; ve spec. t, iS - t a, , , , A functional group may be defined as an atom or a group of atoms present in a molecule, _ which largely determines its chemical properties, “cies, To explain the meaning of a functional group, let us consider ethane (C,Hg) and ethanol or ethy|, , alcohol (C,H,OH) as ¢xamples. Here, ethanol is obtained by replacin, : ; g one hydrogen atom of ethane b, hydroxyl group as shown below : ey a, , H H H H, | | re ED ee gre aga ee Me a, f° 6 eray H—C—C— OH |< Functional, t i i +OH [beeen group, H H Hon, Ethane Ethanol, , Both ethane and ethanol have different physical and chemical properties. For example,, 1. Ethane is a gas while ethanol is a liquid at room temperature., , 2. Ethanol is an antiseptic and a hypnotic (induces sleep) but ethane does not have these properties,, , 3. Ethanol reacts with sodium to form sodium ethoxide with the evolution of hydrogen gas but, ethane does not give this reaction., , From the above discussion, we conclude that the Properties of ethanol are quite different from those of, ethane because during its formation, one of the hydrogen atoms of ethane is replaced by the hydroxyl, (— OH) group. Thus, we see that the properties of ethanol depend upon the hydroxyl group. Thus, hydroxyl, (— OH) group is the functional group of ethanol., , Some important functional groups are given in Table 4.3. The free valency or valencies of the functional, group is/are shown by single line/s. The functional group is attached to the carbon chain: through this/these, free valency/valencies by replacing one or more hydrogen atoms., , , , Ses, , TABLE 4.3, Some Common Functional :, , Name of the functional group, , Chloro, Bromo, Hydroxyl, , , , , m | Formula of the functional group, , , , , , Aldehydic, , , , Ketonic, , , , , , Carboxy]