Straight chains, Branched chains, and Rings of Carbon atoms

1. Carbon can form charcoal when it is heated in the absence of air.
2. It is a unique element that exists in various forms, such as coal and ash, which are pure carbon.
3. The density of carbon varies based on its form and origin.
4. Some forms of carbon are pure, while others, like coal, are mixtures of carbon and hydrogen.
5. Carbon exists in multiple allotropic forms, each having distinct physical and chemical properties.
6. Allotropes are variations of the same element with different characteristics.
7. The colour of carbon is typically soft and appears as a dull grey or black.
8. These properties contribute to carbon's versatility and widespread occurrence in nature.

A straight-chain hydrocarbon consists of carbon atoms joined in a continuous chain without branching. These belong to the alkane family, which contains only single bonds (C–C).

These hydrocarbons are saturated (alkanes) because they contain only single bonds between carbon atoms.

1. Carbon has an atomic number of 6 and an atomic mass of 12.011 g/mol⁻¹.
2. Its electronegativity is 2.5, and its density at 20°C is 2.2 g.cm⁻³.
3. The melting and boiling points are 3652°C and 4827°C, respectively.
4. The Van der Waals radius is 0.091 nm, and the ionic radius is 0.015 nm (+4) or 0.26 nm (-4).
5. Its electronic configuration is He 2s² 2p².
6. The ionisation energies are 1086.1 kJ.mol⁻¹ (first), 2351.9 kJ.mol⁻¹ (second), and 4618.8 kJ.mol⁻¹ (third).
7. Carbon participates in allotropic transformations, such as the conversion between graphite and diamond under high pressure and temperature.
8. Carbon is non-metallic and generally unreactive at room temperature but reacts with oxygen at high temperatures to form carbon dioxide (CO₂) or carbon monoxide (CO).

When a carbon chain has side branches, it forms a branched hydrocarbon. These branches are called alkyl groups, and their presence leads to structural isomerism (same molecular formula, different structure).

Example: Butane (C₄H₁₀) – Two Isomers

This phenomenon is called structural isomerism because the same molecular formula represents different compounds with distinct physical and chemical properties.

Cyclic hydrocarbons have carbon atoms arranged in a closed-ring structure. They can be:

• Saturated (Cycloalkanes): Only single bonds between carbon atoms.
• Unsaturated (Cycloalkenes & Cycloalkynes): contain double or triple bonds within the ring.

Cyclic Hydrocarbon	Molecular Formula	Structural Formula
Cyclopropane	C₃H₆
Cyclobutane	C₄H₈
Cyclopentane	C₅H₁₀
Cyclohexane	C₆H₁₂
Cyclohexene	C₆H₁₀
Benzene (Aromatic Hydrocarbon)	C₆H₆

Benzene and similar compounds are called aromatic hydrocarbons due to their stability and resonance structure.

The compounds having this characteristic unit in their structure are called aromatic compounds.

• Carbon compounds can have straight, branched, or ring chains of carbon atoms.
• Isomers have the same formula but different structures (e.g., butane).
• Crude oil is a mix of hydrocarbons; fuels like LPG and petrol are separated by fractional distillation.
• Saturated hydrocarbons have single bonds, while unsaturated ones have double or triple bonds.
• Aromatic compounds, such as benzene, have rings with alternating double bonds.