Chapter 8 – Compounds of Carbon

Why is Carbon Important?

• Carbon compounds make up over 90% of all chemical compounds.

• They also form the basis of living systems.• The study of carbon compounds is now called

‘Organic Chemistry’.• In its many millions of organic compounds,

carbon is associated with hydrogen and commonly oxygen, sulfur, nitrogen and chlorine.

Week 4, Lesson 1

Why is Carbon Important? Cont…• If 200 atoms were selected from the human body you

would find that 126 atoms were hydrogen, 51 atoms were oxygen, 19 atoms were carbon, 3 atoms were nitrogen and 1 atom of all other elements.

• These proportions are the same when we are born and are maintained throughout life.

• Food that we eat also contain these elements.• Protein, CHO’s and fats all contain carbon, hydrogen and

oxygen.• Proteins are also a source of nitrogen and sulfur and

some contain other elements.• Vitamins and minerals are distributed across a number

of food and introduce traces of other elements that we need in our diets.

How does Carbon form so many Compounds?

• The electronic configuration of carbon is 1s22s22p2. It can form a variety of different compounds because:– Each carbon atom has four valence electrons, all

available for bonding with other atoms– A carbon atom can form strong covalent bonds

with other carbon atoms– Bonds between carbon atoms can be single or

multiple.

Natural Gas

• Is a widely used, clean-burning, efficient and economical fuel. It is vital for out everyday lives.

• Natural gas is used for cooking and heating in homes.

• It is also used in the industry for gas-fired kilns and gas-fired furnaces.

• Some vehicles are powered by compressed natural gas.

Natural Gas cont…• Natural gas is often found with deposits of petroleum.• It is thought that natural gas and petroleum are formed by

the chemical degradation of organic matter from the remains of land and aquatic plants lying in swampy water.

• With a lack of oxygen and, over time, with the build-up of heat and pressure, this material is converted into many different compounds of carbon and hydrogen.

• These compounds, which include molecules of different sizes, are known as hydrocarbons.

• Natural gas is a mixture of many different compounds, mostly small hydrocarbon molecules along with some other chemicals.

Hydrocarbons

• Hydrocarbons can be classified into several series or families.

• The simplest hydrocarbon, CH4, methane is the first in the alkane series.

Alkanes• Compounds which consist of carbon and hydrogen

only.• They only contain single bonds.• Each compound in the alkane series differs by CH2.

• This series is known as a homologous series.• Members of the same homologous series tend to

have very similar chemical properties.• Alkanes have the molecular formula CnH2n+2.

Alkanes cont…

Representing Alkane Molecules

• In structural formulas, the focus is on the location of the atoms relative to one another in the molecule as well as the number and location of chemical bonds.

• Lone pairs are not included in a structural formula.• In each of the alkanes;

– Each carbon atom forms a single bond to four other atoms.

– Each hydrogen atom forms a single bond to one carbon atom

– The four atoms bonded to each carbon atom are arranged in a tetrahedral manner, around the carbon.

Isomers

• When it comes to drawing the structural formula for C4H10, there are two possible arrangements that satisfy these requirements.

Isomers cont…

• You can see in the first structure the four carbon atoms are bonded in a continuous chain. The overall molecule is linear and such are sometimes called straight-chain molecules.

• The second structure has the four carbon atoms bonded in a branched chain.• These two molecules are known as isomers – as the have the same molecular

formula but a different arrangement of the atoms.• Structural isomers have similar chemical properties but differ in some physical

properties such as melting and boiling temperature.

Hydrocarbons

• In the alkanes there are single covalent bonds between the carbons.

• Because of these bonds, alkanes are said to be saturated.

• Because there are only single bonded carbons, each C atom is saturated by hydrogen atoms.

Alkenes

• Ethene is the molecular formula C2H4 and is the first member of the alkenes.

• In alkenes there is one double bond between two carbon atoms.

• Alkenes, like alkanes, differ by CH2, and as such are also known as homologous series.

• They have the general formula of CnH2n.

Alkenes cont…FORMULA NAMEC2H4 Ethene

C3H6 Propene

C4H8 Butene

C5H10 Pentene

C6H12 Hexene

C7H14 Heptene

C8H16 Octene

C9H18 Nonene

C10H20 Decene

Representing Alkene Molecules

• Like the alkane, butene has more than one isomer.• The four carbon atoms and eight hydrogen atoms can be

arranged in more than one way with each carbon atom forming four bonds and each hydrogen atom forming one

• Two of the isomers are straight chained, with the only difference being the position of the double bond.

• The third isomer has a branched chain.• The alkenes are classified as unsaturated hydrocarbons.• The double bond between two of the carbon atoms mean

that alkenes contain less hydrogen that the maximum amount possible.

Butene

Semistructural Formulas• When we want the structural formula to be

summarised without indicating the 3D arrangement of the atoms we use the semistructural formula.

• In a semistructural formula, the carbon atoms and the attached hydrogen atoms, are listed in the order in which they appear in the structural formula.

• Single bonds are not indicated, but any double or triple bonds are shown.

Semistructural Formulas

CH3CH2CH2CH3

CH2=CHCH3

Naming Carbon Compounds

• A naming system was developed in 1960’s to make it easier to name and recognise carbon compounds.

• This naming system was developed by the International Union of Pure and Applied Chemistry (IUPAC).

• This system provides a set of rules by which chemists can derive the systematic name for a given compound.

Week 4, Lesson 2

The Prefixes

Number of Carbon Atoms Prefix1 Meth-2 Eth-3 Prop-4 But-5 Pent-6 Hex-7 Hept-8 Oct-9 Non-10 Dec-

The first part of the name refers to the number of carbons in one molecule (in straight chain hydrocarbons).

Straight Chain Hydrocarbons

• The end of the name is dependent on the type of carbon bonds.

• The name of the the hydrocarbon ends in:– ane: if all carbon-carbon bonds are single bonds– ene: if one of the carbon-carbon bonds is a double

bond– yne: if one of the carbon-carbon bonds is a triple

bond.

Unsaturated Compounds

• To name unsaturated straight chain hydrocarbons:

1. Number the carbon atoms in the chain, starting at the end that will give the first carbon involved in a double bond, the smallest number possible.

2. Distinguish which prefix and ending should be used.3. Name the hydrocarbon with the prefix, then the

number of the carbon that has the double bond, then the ending.

Example…

• But-1-ene

• But-2-ene

Branched Hydrocarbons

• An alkyl group often forms a branch in a branched-chain hydrocarbon.

• An alkyl group is an alkane molecule less one hydrogen atom and is named based on the alkane it is derived from. Eg –CH3 is a methyl group.

Naming Branched Hydrocarbons

• Systematic naming requires us to:– Identify the longest chain of carbon atoms in the

molecule.– Identify the side group that forms the branch in

the chain– Number the carbon atoms from one of the ends

of the longest chain so that the side group is attached to the carbon with the smallest number possible.