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The hydrocarbons

Let us first look at a group of organic compounds known as the hydrocarbons . These molecules only contain carbon and hydrogen. The hydrocarbons that we are going to look at are called aliphatic compounds . The aliphatic compounds are divided into acyclic compounds (chain structures) and cyclic compounds (ring structures). The chain structures are further divided into structures that contain only single bonds ( alkanes ), those that contain at least one double bond ( alkenes ) and those that contain at least one triple bond ( alkynes ). Cyclic compounds include structures such as the benzene ring . [link] summarises the classification of the hydrocarbons.

The classification of the aliphatic hydrocarbons

Hydrocarbons that contain only single bonds are called saturated hydrocarbons because each carbon atom is bonded to as many hydrogen atoms as possible. [link] shows a molecule of ethane which is a saturated hydrocarbon.

A saturated hydrocarbon

Hydrocarbons that contain double or triple bonds are called unsaturated hydrocarbons because they don't contain as many hydrogen atoms as possible. [link] shows a molecule of ethene which is an unsaturated hydrocarbon. If you compare the number of carbon and hydrogen atoms in a molecule of ethane and a molecule of ethene, you will see that the number of hydrogen atoms in ethene is less than the number of hydrogen atoms in ethane despite the fact that they both contain two carbon atoms. In order for an unsaturated compound to become saturated, a double bond has to be broken, and another two hydrogen atoms added for each double bond that is replaced by a single bond.

An unsaturated hydrocarbon

Interesting fact

Fat that occurs naturally in living matter such as animals and plants is used as food for human consumption and contains varying proportions of saturated and unsaturated fat. Foods that contain a high proportion of saturated fat are butter, ghee, suet, tallow, lard, coconut oil, cottonseed oil, and palm kernel oil, dairy products (especially cream and cheese), meat, and some prepared foods. Diets high in saturated fat are correlated with an increased incidence of atherosclerosis and coronary heart disease according to a number of studies. Vegetable oils contain unsaturated fats and can be hardened to form margarine by adding hydrogen on to some of the carbon=carbon double bonds using a nickel catalyst. The process is called hydrogenation

We will now go on to look at each of the hydrocarbon groups in more detail. These groups are the alkanes, the alkenes and the alkynes.

The alkanes

The alkanes are hydrocarbons that only contain single covalent bonds between their carbon atoms. This means that they are saturated compounds and are quite unreactive. The simplest alkane has only one carbon atom and is called methane . This molecule is shown in [link] .

The structural (a) and molecular formula (b) for methane

The second alkane in the series has two carbon atoms and is called ethane . This is shown in [link] .

The structural (a) and molecular formula (b) for ethane

The third alkane in the series has three carbon atoms and is called propane ( [link] ).

Questions & Answers

The phenomenon that describes the change in the frequency
Neo Reply
Doppler effect
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mudodzwa Reply
formula of heat reaction
Anelisiwe Reply
final energy-initial energy of substances
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Joy Reply
Ethane is a saturated organic molecule while ethene is unsaturated Ethane has 2 carbon atoms and 6 hydrogen atoms, while ethene has 2 Carbons and 4 hydrogens Ethane has single bond between the 2 Carbon atoms while ethene has double bond
How do you know that the reaction is in acid medium or basic medium
Miss Reply
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Ansiwe Reply
doppler effect is the perceived change in frequency of a sound caused by either the source or the listener
moving relative to each other
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It does this by lowering the activation energy.
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reaction that releases energy
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The first thing you can do is to understand ohm's law and the difference between a series and parallel connection concerning current, resistance and potential difference
Hi Xiluva,not sure if this will be helpful but to understand electricity better I suggest you download Siyavula physical science books there's both a learner book and a teacher's guide I was struggling too they really did help you might be able to do some exercises after reading siyavula material
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temperature surface area concentration addition of a catalyst
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How to calculate e.p
zama Reply
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chemical compound with molecules bonded together in long ,repeating chains
hey guys i need help with the topic of forces and their application
Monica Reply
A force is a pull or push and it can be applied in rocket launchers moving cars & stoping (breaking them).
A force is that Agency which changes the object's state of rest or motion. A push or pull are the effects of force.

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Source:  OpenStax, Siyavula textbooks: grade 12 physical science. OpenStax CNX. Aug 03, 2011 Download for free at http://cnx.org/content/col11244/1.2
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