Question

What are the general formulas for alkane, alkene, alkyne, alkyl, aldehyde, ketone and cycloalkane?

Answer 1

Hint : Hydrocarbons differ by the difference in the bonding between carbon-carbon atoms and by different functional groups added to them. Alkanes have a single bond, alkenes have a double bond and alkynes have a triple bond between the carbon atoms. Aldehydes have a single bond with the carbonyl group whereas ketones have two carbon atoms attached to the carbonyl group. Cycloalkanes are the cyclic hydrocarbons.

Complete Step By Step Answer:
The simplest organic compounds containing only the elements carbon and hydrogen are called hydrocarbons. There are different types of hydrocarbons that differ in the length of the chains, structure, functional group and most importantly carbon-carbon bonding.
We distinguished following types of the hydrocarbon on the basis of bonding between the carbon atoms and functional group-
1. Alkanes.
Alkanes are the saturated hydrocarbon which contains only single covalent bonds between carbon atoms. Each of the carbon atoms is $s{p}^3$ hybridized and bonded to four other atoms. The general formula for alkane is $C_n{H}_{2n+2}$ , where n is any integer equal to or greater than 1.The simplest alkane is methane having one carbon atom and molecular formula $C{H}_4$ ,
2. Alkene.
Alkenes are the unsaturated hydrocarbons that have at least one carbon and carbon double bond. The doubly bonded carbon atoms are $s{p}^2$ hybridized. The general formula for alkene is $C_n{H}_{2n}$ , where n is any integer greater than 1.The simplest alkene is ethene containing two carbons and having molecular formula $C_2{H}_4$ .
3. Alkyne.
Alkynes are the unsaturated hydrocarbons that have at least one carbon and carbon triple bond. The triply bonded carbon atoms are $sp$ hybridized. The general formula for alkyne is $C_n{H}_{2n-2}$ , where n is any integer greater than 1.The simplest alkyne, ethyne has two carbon atoms and having molecular formula $C_2{H}_2$ .
4. Alkyl.
An alkyl group is formed by removing one hydrogen from alkane which makes the general formula of alkyl as $C_n{H}_{2n+1}$ .By removing one hydrogen from alkane changes the name of the group from –ane to –yl. For example after removing one hydrogen from methane it becomes a methyl group.
5. Aldehyde.
Aldehydes are the group in which the carbonyl group is single-bonded to a hydrogen atom. A carbonyl is a carbon that is double bonded to an oxygen atom. The general formula for aldehyde group is $C_n{H}_{2n+1}CHO$ or $C_n{H}_{2n}O$ .The simplest aldehyde is Formaldehyde $HCHO$ .
6. Ketone.
Ketone is the group in which two carbon atoms or groups are attached to the carbonyl carbon atom. The general formula for the ketone is $C_n{H}_{2n}O$ .The simplest ketone is acetone having formula $C{H}_{3}C(O)C{H}_3$ .
7. Cycloalkane.
Cycloalkanes are the cyclic hydrocarbons, it means that carbon molecules in it are arranged in the form of a ring. Cycloalkanes are saturated; it means that carbon compound forming rings are all singly bonded. The general formula for cycloalkanes are $C_n{H}_{2n}$ .

Note :
Remember the name of different kinds of hydrocarbons and how they are different in terms of bonding and attached functional group. If you remember this it will be easy to understand the general formula. If you also remember the simplest compound of different hydrocarbons you yourself can deduce the general formula by observing the pattern.