Hydrocarbons

A hydrocarbon is a type of organic chemical compound made up only of carbon (C) and hydrogen (H) atoms. The carbon atoms form the structure of the compound, while hydrogen atoms are attached to them in various arrangements.

• Hydrocarbons are the main components of petroleum and natural gas. Carbon, with an electronic configuration of 2,4, requires four additional electrons to complete its octet and become stable like the inert gas neon (2,8).
• Instead of gaining or losing electrons, carbon shares its electrons through covalent bonding. This allows a carbon atom to form four covalent bonds, either with other carbon atoms or with atoms of other elements.
• For example, when a carbon atom bonds with four hydrogen atoms by sharing electrons, it forms a methane molecule (CH₄), which is the simplest hydrocarbon.
• They are widely used as fuels and lubricants and serve as raw materials for producing plastics, fibres, rubbers, solvents, explosives, and many industrial chemicals.

Saturated hydrocarbons are hydrocarbons in which all carbon atoms are bonded to other atoms through single covalent bonds (C–C). Each carbon atom forms four single bonds, fully occupying its bonding capacity. They are the simplest and least polar organic compounds found in nature. Examples of saturated hydrocarbons include the alkane and cycloalkane families.

General formula: CₙH₂ₙ₊₂

For example:

Line structure / structural formula of ethane

\[\begin{array}{cc}
\ce{\phantom{}H\phantom{..}H}\\
\phantom{}|\phantom{...}|\\
\ce{H-C-C-H}\\
\phantom{}|\phantom{...}|\\
\ce{\phantom{}H\phantom{..}H}\\
\end{array}\]

Electron-dot structure of ethane

\[\begin{array}{cc}
\phantom{}\ce{H}\phantom{....}\ce{H}\phantom{}\\
\phantom{}\ce{H}\phantom{..}\ce{\text{}^\bullet_\bullet}\phantom{..}\ce{\overset{\bullet\phantom{.}\bullet}{\underset{\bullet\phantom{.}\bullet}{C}}}\phantom{..}\ce{\text{}^\bullet_\bullet}\phantom{..}\ce{\overset{\bullet\phantom{.}\bullet}{\underset{\bullet\phantom{.}\bullet}{C}}}\phantom{..}\ce{\text{}^\bullet_\bullet}\phantom{..}\ce{H}\phantom{}\\
\phantom{}\ce{H}\phantom{....}\ce{H}\phantom{}\\
\end{array}\]

Unsaturated hydrocarbons are hydrocarbons that contain one or more double or triple bonds between carbon atoms. More reactive than saturated hydrocarbons. Furthermore, their reactivity increases with the number of multiple bonds present in the main carbon chain.

Two types:

1. Alkenes – Have at least one double bond (C=C).

General Formula: CnH2n

2. Alkynes – Have at least one triple bond (C≡C).

General Formula: CnH(2n-2)

For example:

Line structure/ structural formula

\[\begin{array}{cc}
\ce{\phantom{}H\phantom{..}H}\\
\phantom{}|\phantom{...}|\\
\ce{C=C}\\
\phantom{}|\phantom{...}|\\
\ce{\phantom{}H\phantom{..}H}\\
\end{array}\]

Electron-dot structures of ethene

\[\begin{array}{cc}
\phantom{...}\ce{H}\phantom{......}\ce{H}\phantom{.}\\
\phantom{..}\ce{\overset{\bullet\phantom{.}\bullet}{\underset{\bullet\phantom{.}\bullet}{C}}}\phantom{..}\ce{\text{}^\bullet_\bullet}\phantom{}\ce{\text{}^\bullet_\bullet}\phantom{..}\ce{\overset{\bullet\phantom{.}\bullet}{\underset{\bullet\phantom{.}\bullet}{C}}}\\
\phantom{...}\ce{H}\phantom{......}\ce{H}\phantom{.}\\
\end{array}\]

Ethyne (CH≡CH)

\[\begin{array}{cc}
\ce{H-C ≡ C-H}\\
\end{array}\]

Propene (CH₃-CH=CH₂)

\[\begin{array}{cc}
\ce{\phantom{....}H\phantom{..}H\phantom{..}H}\\
\phantom{....}|\phantom{...}|\phantom{...}|\\
\ce{H-C-C=C}\\
\phantom{....}|\phantom{......}|\\
\ce{\phantom{....}H\phantom{.....}H}
\end{array}\]

Propyne (CH≡C-CH₃)

\[\begin{array}{cc}
\ce{\phantom{.......}H}\\
\phantom{..........}|\phantom{...}\\
\ce{H-C≡C-C-H}\\
\phantom{.......}|\\
\ce{\phantom{.......}H}
\end{array}\]