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Carbon compounds make up over 90% of all chemical compounds and form the basis of living systems. This lesson explores why carbon is important and how it forms a wide variety of compounds. It also discusses the role of natural gas and hydrocarbons in our everyday lives.
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Week 4, Lesson 1 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.
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.
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.
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.
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 whichthey appear in the structural formula. • Single bonds are not indicated, but any double or triple bonds are shown.
Semistructural Formulas CH3CH2CH2CH3 CH2=CHCH3
Week 4, Lesson 2 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.
The Prefixes 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: • 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. • Distinguish which prefix and ending should be used. • 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.
