This question is about compounds of carbon - AQA - GCSE Chemistry - Question 2 - 2017 - Paper 1

The central part of the carbon atom is made up of six neutrons that have no electrical charge and six protons which are positively charged. Thus, it can be described as:

• The central part contains six protons, which are positively charged.
• Together with neutrons, they form the nucleus of the atom.
• The nucleus is responsible for the atom's mass.

A hydrocarbon is made up of hydrogen and carbon (atoms) only. These molecules can consist solely of carbon and hydrogen atoms arranged in various structural forms.

The displayed structure of ethane ($C_2H_6$) is:

   H   H
   |   |
H–C–C–H
   |   |
   H   H

The displayed structure of ethene ($C_2H_4$) is:

   H   H
   |   |
H–C=C–H
   |   |
   H   H

Note that ethene has a double bond between the carbon atoms.

As the number of carbon atoms increases in an alkane molecule, the boiling point of the alkane molecule increases. This trend is due to larger alkane molecules exhibiting greater London dispersion forces, which require more energy to overcome.

The boiling points of alkanes are generally higher than the boiling points of alkenes that have the same number of carbon atoms. For instance:

• Hexane ($C_6H_{14}$) boils at 69°C, while hexene ($C_6H_{12}$) boils at 64°C.
• This trend can be attributed to the presence of double bonds in alkenes, which result in weaker intermolecular forces compared to the saturated alkanes.

When liquid paraffin (which contains alkanes) is heated to a high temperature, the alkane molecules undergo cracking. This process breaks down larger alkane molecules into smaller ones, including smaller alkanes and alkenes. This thermal decomposition causes the alkanes to break down into gaseous products, which can lead to the formation of more reactive unsaturated hydrocarbons.