Hydrocarbons and Functional Groups
NCERT Class 10 • Science • Chapter "Carbon and Its Compounds"
Hydrocarbons and Functional Groups
A hydrocarbon contains only carbon and hydrogen. When all carbon to carbon bonds are single the compound is saturated; when a double or triple bond is present it is unsaturated, and this single distinction governs most of its chemistry.
Saturated and Unsaturated Compounds
- Alkanes have only single bonds and are saturated; methane, ethane, propane and butane are the first four.
- Alkenes contain a carbon to carbon double bond and alkynes a triple bond, so both are unsaturated.
- Unsaturated compounds are more reactive than saturated ones and readily undergo addition reactions.
- Saturated hydrocarbons burn with a clean blue flame while unsaturated ones burn with a sooty yellow flame.
- Addition reaction adds hydrogen across a double bond in the presence of a catalyst such as nickel, which is how vegetable oil is hardened into vanaspati.
- Substitution reaction replaces a hydrogen atom of an alkane, typically with a halogen in sunlight.
- A homologous series is a family of compounds with the same functional group where each member differs from the next by a fixed unit.
Functional Groups, Ethanol and Ethanoic Acid
- A functional group is the atom or group of atoms that decides the chemical properties of a compound.
- The main groups are alcohol, aldehyde, ketone, carboxylic acid and halogen.
- Members of a homologous series have similar chemical properties and a gradual change in physical properties.
- Ethanol is the alcohol present in alcoholic drinks; it is a liquid at room temperature and is used as a solvent and in medicines.
- Ethanol reacts with sodium to release hydrogen and, on heating with concentrated sulphuric acid, gives ethene.
- Ethanoic acid, the acid in vinegar, freezes in cold climates and is therefore called glacial acetic acid.
- Ethanoic acid reacts with an alcohol in the presence of an acid catalyst to give a sweet smelling ester, a reaction called esterification.
| Compound Type | Bond Present | Reactivity |
|---|---|---|
| Alkane | Only single bonds | Least reactive, substitution |
| Alkene | One double bond | More reactive, addition |
| Alkyne | One triple bond | Most reactive of the three |
Functional group — the atom or group of atoms in a carbon compound that determines its chemical properties.
Exam me kaise aata hai
- Hardening of vegetable oil is an example of — addition reaction
- Ethanoic acid is commonly known as — vinegar acid
- Pure ethanoic acid is called — glacial acetic acid
- A sweet smelling compound from acid and alcohol is an — ester
UPSC/State PSC ke liye
- Unsaturated compounds are more reactive because a double or triple bond can open up and accept more atoms, which a single bond cannot.
- A homologous series matters because knowing one member's chemistry lets you predict the whole family's, which is why organic chemistry is learnt by group rather than by compound.
Yahan confuse hote hain
✗ Saturated compounds are more reactive | Unsaturated compounds are more reactive | ✓
✗ Alkenes have a triple bond | Alkenes have a double bond; alkynes have a triple bond | ✓
✗ A sooty flame means a saturated hydrocarbon | A sooty flame indicates an unsaturated hydrocarbon | ✓
Ek nazar me
- Hydrocarbons are saturated with single bonds or unsaturated with double or triple bonds.
- Unsaturated compounds undergo addition; alkanes undergo substitution.
- A functional group decides the chemical properties of a compound.
- Ethanol and ethanoic acid are the two most important carbon compounds in the syllabus.