HHyyddrrooccaarrbboonnssChapter 8:

What is carbon chemistry?

• Compounds containing Carbon make up 90% of all chemicals and form the basis of living things

• Organic chemistry is the study of Carbon compounds

How does Carbon form so many compounds?

The electronic configuration of carbon is 1s22s22p2.

It can form a wide variety of 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.

Hydrocarbons• Compounds made up

of Hydrogen and Carbon are known as Hydrocarbons

• Hydrocarbons can be classified into several series or families

• The first series is known as the “alkanes”

Alkanes• Are a family that consist of

carbon and hydrogen only• They contain only single

bonds• CnH2n+2

• Compounds that differ only by –CH2- belong to the same homologous series

• Compounds of the same homologous series share the similar chemical properties

Representing AlkanesWe use structural formulas to

represent hydrocarbons

You will notice that each carbon atom: • forms a single covalent bond to four

other atoms• each hydrogen atom forms a single

covalent bond to one carbon atom• the four atoms bonded to each

carbon atom are arranged in a tetrahedral manner around the carbon.

Structural IsomersWhen we come to draw a structural formula for C4H10, however, there are two

possible arrangements that satisfy the bonding requirements of each of the four carbon atoms and ten hydrogen atoms

These two compounds are structural isomers. That means that they have the same molecular formula (C4H10) but a different

arrangement of their atoms.

Structural isomers have similar chemical properties but differ in some physical properties such as melting and boiling temp.

Structural Isomers

As molecules become larger, the number of possible arrangements of atoms increases rapidly.

Saturated HydrocarbonsThe alkanes are known as saturated hydrocarbons. Because there are only single bonds between carbon atoms, they are

‘saturated’ with hydrogen atoms.

Carbon and hydrogen can also form families of compounds in which there are double or triple bonds between carbon atoms. These compounds are unsaturated as they do not contain the maximum number of H atoms.

Naming AlkanesAlkanes use the prefix relevant to the number of Carbons, and ends in “ane”.

Four things you may be asked for:1.Name the compound2.Write the molecular formula3.Draw the Structural formula4.Write the condensed structural formula (semi-structural)

AlkenesThe alkenes form a new homologous series. Their members differ by -CH2- and

contain a single double bond between two carbon atoms and share similar chemical properties.

CnH2n

Alkenes are unsaturated as they contain less than the maximum amount of Hydrogens possible. They are named using the same prefix and end in “ene”.

Isomers exist in Alkenes as well. Isomers can be branched, straight chain or even a different position of the double bond.

Your Turn:1. Complete the Handout

• Name the alkanes• Draw the Structural formula• Write the semi-structural (condensed) formula• Write the molecular formula

2. Chapter 8 Review Questions• Q 2, 3, 4, 5, 6

3. Complete the second handout of challenge questionsDon’t forget – SACT due next Wednesday!!

Check the blog and keep up to date!!

Naming Organic CompoundsIUPAC (International Union of Pure and Applied

Chemisty) created a common set of naming rulesRules:1.Determine the longest chain of carbon atoms2.Determine which end is nearest to a branch, double bond or triple bond3.Number the carbon atoms from the end chosen4.Name any branches first with the ending –yl, then the longest chain, then any single or double bond5.When two or more branches occur on the same carbon atom, the number of the carbon atom is indicated for each branch6.When two or more identical branches occur on different carbon atoms, the prefixes di, tri and tetra are used

Avoid the common errors:•Not identifying the longest chain•Not listing the side branches in alphabetical answer•Omitting the prefixes di, tri and tetra

Naming Organic CompoundsThere are a set of rules used to name carbon compounds to distinguish between different

isomers

In the systematic naming of straight-chain hydrocarbons, the first part of the name refers to the number of carbon atoms in one molecule

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

Example - Naming straight chain alkenes

To name straight-chain alkenes, first number the carbon atoms in the chain, starting at the end that will give the first carbon atom involved in the double bond the smallest number possible.

The numbering of the chain starts at this end and the isomer is named according to the first carbon atom involved in the double bond.

But-1-eneBut-2-ene

Branched HydrocarbonsAn alkyl group most often forms a branch in a branched-

chain hydrocarbon.An alkyl group is an alkane molecule less one hydrogen

atom and is named after the alkane from which it is derived. For example, –CH3 is a methyl group,

Systematic naming requires us to:• identify the longest continuous chain of carbon atoms in the molecule and the series the molecule belongs to (alkane/alkene/alkyne)

• identify the side group that forms the branch in the chain

• number the carbon atoms from one of the ends of the longest carbon chain so that the side group is attached to the carbon atom with the smallest number possible.

Branched Hydrocarbons – Have a go

Your Turn – practice makes perfect!Review Questions:

1. Chapter 8:• Q7• Q8 (draw as well as name each of these)

2. Write the structural formula for:a) hex-2-ene b) 2-methylpropene c) 2-pentyned) 4-methylpent-2-ene e) 2,4-dimethylhexanef) 3,3-dimethylpentane g) 3-ethyl-2,4-dimethyloctaneh)3-ethylheptanei) 4-ethyl-3-methylhex-2-enej) 3-ethyl-4,5-dipropyloctane

Functional GroupsThe majority of carbon compounds contain other

elements in addition to hydrogen. Taking an alkane and replacing a hydrogen atom with

another atom or group of atoms changes the chemical properties of the compound.

An atom or group of atoms that influence the properties of the compounds forming a homologous series is known as a functional group

Hydroxyl group - OHAlcohols have the functional group OH. A functional group is a group of atoms that gives the

molecule unique chemical properties. Molecules with the hydroxyl group (OH) are very soluble

in water, depending on their molecular size.A “H” atom is replaced by an OH groupThe last part of the name is replaced with an “ol”

Methanol Butanol

Carboxyl group - COOHCarboxylic acids have the functional group COOH. Molecules with the carboxyl functional group (COOH) are

known as organic acids. They dissolve in water to form acidic solutions.

The COOH group is made up of:2 H atoms are replaced by “COOH” group The last part of the name becomes “-anoic acid”

Propanoic Acid Ethanoic Acid

Halogens - (Cl, Br, I, F)Cl – chloroalkanes Br - BromoalkanesF – Fluoroalkanes I - Idoalkanes A “H” atom is replaced by a HalogenThe first part of the halogen is said in front of the alkane

Chloroethane 2-Bromopropane

Physical PropertiesAs the number of carbon atoms increases, members of a

homologous series show a gradual change in their physical properties.

Compounds with smaller molecules are more volatile than larger molecules

Less energy is needed to break bonds of smaller moleculesSmaller molecules have a lower viscosityThe boiling temperature increases as molecules get largerThis is true for Alkanes and Alkenes. If an alkane and alkene have the same number of carbons

then they will have a similar boiling temp, although an alkenes will be slightly lower.

Physical Properties – WHY?The bonding within hydrocarbons is covalent (strong), however,

hydrocarbons are non-polar. The forces between molecules are dispersion forces which increase in strength as the molecule gets bigger.

More energy is required to overcome the dispersion forces between larger hydrocarbon molecules, so a higher temperature is required to boil

Volatility (tendency to evaporate): The stronger the dispersion forces between molecules in the liquid state, the lower the tendency for the liquid to evaporate and so the lower the volatility.

The higher viscosity of the longer-chain hydrocarbons is due to the tendency of longer molecules to become ‘tangled’ together

Chemical Properties of AlkanesThe most significant reaction of alkanes for our society is

combustion. Alkanes burn in oxygen, releasing large quantities of

energy. If the supply of oxygen is sufficient, the products of the

reaction are carbon dioxide and water. We use the energy released by the combustion of alkanes

as a source of heat, to produce electricity for domestic and industrial use and in transportation.

Combustion Reactions

Don’t forget to add in the states (g, aq, l)