In-depth Notes on Hydrocarbons and Their Properties

Carbon is unique due to its ability to form more compounds than any other element, attributed to:
- Four valence electrons that allow formation of covalent bonds with four different atoms.
- Formation of strong covalent bonds with other carbon atoms.
- Ability to create single, double, or triple covalent bonds.
Carbon can bond with itself to form varied molecules that differ in length, shape, properties, and applications.
Compounds made only of carbon and hydrogen are called hydrocarbons.

The naming conventions for hydrocarbons are provided by IUPAC and take into account the number of carbon atoms in the compound.
Stem names indicate the number of carbon atoms:
- Meth- (1), Eth- (2), Prop- (3), But- (4), Pent- (5), Hex- (6), Hept- (7), Oct- (8), Non- (9), Dec- (10).
Alkanes, represented as saturated hydrocarbons, have only single bonds between carbons. The general formula for alkanes is $CnH{2n+2}$ .
The systemic naming for alkanes includes the suffix -ane (e.g., pentane for 5 carbons).
- Example: If an alkane has 12 carbon atoms, the hydrogen count is calculated as: $2n + 2 = 2(12) + 2 = 26$ , resulting in $C{12}H{26}$ .
Alkanes can be represented through different formulas:
- Molecular formula (e.g., $C2H6$ for ethane)
- Structural formula (shows arrangement and bonds)
- Semi-structural formula (condensed version of structural formula)

Alkanes with 4 or more carbons can have different structures (isomers). For instance:
- Butane can exist as both normal and branched structures (2-methylpropane).
Structural isomers share the same molecular formula but differ in structure, leading to different chemical and physical properties.
Naming involves identifying the longest carbon chain, numbering from one end to minimize the numbering for side chains, and using prefixes (di-, tri-) as needed.
- Example: 2-methylpentane indicates a methyl group on the 2nd carbon.

Physical properties include solubility, melting points, and boiling points determined by intermolecular forces. Alkanes are non-polar and insoluble in water.
As carbon chain length increases, boiling and melting points rise due to stronger dispersion forces between molecules.
For alkanes:
- Example: Methane $C1H4$ - gas, boiling point -164°C
- Ethane $C2H6$ - gas, boiling point -87°C
- Propane $C3H8$ - gas, boiling point -42°C

Complete combustion occurs with sufficient oxygen, producing $CO2$ and $H2O$ , releasing energy (e.g., burning methane).
- Complete combustion of methane: CH4(g) + 2O2(g)
 ightarrow CO2(g) + 2H2O(l).
Incomplete combustion occurs with limited oxygen, producing carbon monoxide or soot along with water, and releases less energy.
- Includes states like Bunsen flames with closed air holes leading to yellow flames.

Alkenes are unsaturated hydrocarbons containing at least one carbon-carbon double bond, with the general formula $CnH{2n}$ .
The simplest alkene is ethene (ethylen, $C2H4$ ), and with each subsequent member in the series (e.g., propene, butene), the alkene will have an increased number of carbon atoms.
Alkenes are more reactive than alkanes due to the double bond and can undergo addition reactions, where the double bond is broken and atoms from reactants are added.
Physical properties are similar to alkanes as they are non-polar and increase in boiling point with chain length.
- Example: Ethene - BP of -78.4°C and Propene - BP of -47.7°C
Addition Reactions: Alkenes can react with bromine water, resulting in a color change indicating unsaturation.
- Example of reaction with bromine: C2H4 + Br2 ightarrow C2H4Br2.

Example: Naming an alkene with a double bond on carbon number 2 with a side chain on carbon 4 results in 4-methylpent-2-ene.