Structure of Alkanes
Applied Science: BTEC Level 3 National Extended Diploma, topic 4.3.5
The Structure of Alkanes
Alkanes are hydrocarbons, so contain only hydrogen and carbon atoms. Alkanes are fully saturated molecules, meaning that they only contain C-H and C-C bonds.
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Sigma (σ) bonds
- The C-H and C-C bonds found in alkanes are known as σ bonds.
- In σ bonds, the electron orbitals overlap directly between the two atomic nuclei.
- σ bonds also allow free rotation of the atoms at either end.
General formula
- For every n carbon atoms, there will be 2n+2 hydrogen atoms in an alkane.
- CnH2n+2 is the general formula for the entire homologous series of alkanes, whether straight-chain or branched.
Carbon atom bond angles
- Every carbon atom in an alkane is bonded to four other atoms (either H or C) via single covalent bonds.
- Electron pair repulsion theory states that regions of negative charge about an atom will repel to be as far apart from each other as is possible in a sphere.
- Four regions of negative charge around each carbon atom in an alkane repel to form a tetrahedral arrangement of bonds, with the angle between the bonds at 109.5o.
Test yourself on Structure of Alkanes
What type of bonds are found in alkanes?
What is the angle between the bonds in a tetrahedral arrangement of bonds?
What is the general formula for all alkanes, whether straight-chain or branched?