Carbon and its Compounds PDF

bonds with other elements such as halogens, oxygen, nitrogen and sulphur. In a hydrocarbon chain, one or more hydrogens can be replaced by these elements, such that the valency of carbon remains satisfied. In such compounds, the eleme...

bonds with other elements such as halogens, oxygen, nitrogen and sulphur. In a hydrocarbon chain, one or more hydrogens can be replaced by these elements, such that the valency of carbon remains satisfied. In such compounds, the element replacing hydrogen is referred to as a heteroatom. These heteroatoms are also present in some groups as given in Table 4.3. Table 4.3 Some functional groups in carbon compounds These heteroatoms and the group containing Hetero Class of Formula of these confer specific atom compounds functional group properties to the compound, regardless of the length and nature Cl/Br Halo- (Chloro/bromo) —Cl, —Br of the carbon chain and alkane (substitutes for hence are called hydrogen atom) functional groups. Some Oxygen 1. Alcohol —OH important functional groups are given in the Table 4.3. Free valency or 2. Aldehyde valencies of the group are shown by the single line. The functional group is attached to the carbon 3. Ketone chain through this valency by replacing one 4. Carboxylic acid hydrogen atom or atoms. 4.2.4 Homologous Series You have seen that carbon atoms can be linked together to form chains of varying lengths. These chains can be branched also. In addition, hydrogen atom or other atoms on these carbon chains can be replaced by any of the functional groups that we saw above. The presence of a functional group such as alcohol decides the properties of the carbon compound, regardless of the length of the carbon chain. For example, the chemical properties of CH3OH, C2H5OH, C3H7OH and C4H9OH are all very similar. Hence, such a series of compounds in which the same functional group substitutes for hydrogen in a carbon chain is called a homologous series. Let us look at the homologous series that we saw earlier in Table 4.2. If we look at the formulae of successive compounds, say – CH4 and C2H6 — these differ by a –CH2- unit C2H6 and C3H8 — these differ by a –CH2- unit What is the difference between the next pair – propane and butane (C4H10)? Can you find out the difference in molecular masses between these pairs (the atomic mass of carbon is 12 u and the atomic mass of hydrogen is 1 u)? Similarly, take the homologous series for alkenes. The first member of the series is ethene which we have already come across in Section 4.2.1. What is the formula for ethene? The succeeding members have the formula C3H6, C4H8 and C5H10. Do these also differ by a –CH2– 66 Science 2024-25