Alkanes
Cards (7)
- Alkanes:
- Alkanes are the main components of natural gas & crude oil
- Mainly used as fuels, exploiting their reaction with oxygen to generate heat.
- Have general formula of CnH2n+2
- Alkanes are saturated hydrocarbons
- Bonding in alkanes:
- Each carbon atom in alkane is joined to 4 other atoms by single covalent bonds. These are a type of covalent bond called a sigma bond
- Sigma bond --> result of the overlap of 2 orbitals, one from each bonding atoms
- Each overlapping orbital contains one electron, so the sigma bond has 2 electrons that are shared between the bonding atoms.
- A sigma bond is positioned on a line directly between bonding atoms.
- Each carbon atom in an alkane has 4 sigma bonds, either C-C or C-H
- Shape of alkanes:
- Each carbon atom is surrounded by 4 electron pairs in 4 sigma bonds
- Repulsion between these electron pairs results in a 3D tetrahedral arrangement around each carbon atom.
- Each bond angle is approximately 109.5 degrees
- Melting and boiling point of alkanes:
- As the number of carbon atoms in the molecules increases, the melting and boiling points increases
- Alkanes have low melting & boiling points due to the weak intermolecular forces of attraction
- straight chain alkanes have higher boiling points than both branched and cyclic alkanes, as they have a greater surface contact area so a greater number and stronger London forces
- As the number of carbon atoms in the molecules increases, they become more viscous (flow less easily)
- This is due to the stronger intermolecular forces of attraction and larger molecules get tangled together easily
- As the number of carbon atoms in the molecules increases, they become less flammable (more difficult to burn)
- The larger alkane molecules contain a higher percentage of carbon and this makes it more difficult to burn
- The larger alkanes also tend to produce a smokier flame due to incomplete combustion of the alkane molecules
- Alkanes are insoluble in water but soluble in organic solvents such as CCl4