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Unit 2 Module 1 Notes

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CHEMISTRY

2.1.1 BASIC CONCEPTS HYDROCARBONS

Contain carbon and hydrogen only

SATURATED HYDROCARBONS

Alkanes Cycloalkanes

FUNCTIONAL GROUP

Molecules with the same functional group react in a similar way

SHAPE OF ALKANES

Tetrahedral

109.5⁰

HOMOLOGOUS SERIES






Alkane Alkene Halogenoalkane Alcohol Aldehyde Ketone Carboxylic acid

FINDING THE EMPIRICAL FORMULA

Find molar ratio (mass in g or percentage over molar mass) Divide by smallest number

FINDING THE MOLECULAR FORMULA


Find the relative empirical mass (molar mass) of the empirical formula Divide the relative molecular mass over the relative empirical mass Multiply empirical formula by this coefficient

GENERAL FORMULA OF ALKANES

CnH2n+2

GENERAL FORMULA OF ALKENES

CnH2n

GENERAL FORMULA OF ALCOHOLS

CnH2n+1OH

CARBOXYL GROUP STRUCTURAL FORMULA

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COOH

ESTER GROUP STRUCTURAL FORMULA

COOR

ALDEHYDE GROUP STRUCTURAL FORMULA

CHO

E/Z ISOMERISM

Occurs because of the restricted rotation of the C=C bond

CRITERIA TO HAVE E/Z ISOMERISM



A carbon-carbon double bond must be present Each carbon in the double bond must be attached to two different groups E-isomer has groups on opposite sides Z-isomer has groups on same side

CIS-TRANS ISOMERISM


Two of the substituent groups are the same attached to each carbon Cis isomer has groups on the same side Trans isomer has groups on opposite sides

BOND FISSION

Covalent bonds are broken

HOMOLYTIC FISSION

Each bonded atom takes one of the shared pair of electrons Forms two radicals

HETEROLYTIC FISSION

One of the bonded atoms takes both of the shared pair of electrons A cation and an anion are formed

NUCLEOPHILE


Often negative ions with a lone pair of electrons Attacks electron-deficient atoms E.g. :Br-, :OH-, H2O:, :NH3

ELECTROPHILE


Often positive ions Attacks electron-rich atoms E.g. Br2, HBr, NO2+

ADDITION REACTION

2 reactants  1 product Unsaturated  saturated

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SUBSTITUTION REACTION

2 reactants  2 products

ELIMINATION REACTIONS

1 reactant  2 products Saturated  unsaturated

2.1.2 ALKANES CRUDE OIL

Source of hydrocarbons It does not ignite easily and so it is not very useful in its native state

FRACTIONAL DISTILLATION


Crude oil is refined in a distillation plant Crude oil is separated as fractions with different boiling points Longer-chained hydrocarbons with higher boiling points condense nearer to the bottom

FRACTIONS







Bitumen (400⁰C) Industrial fuel oil (370⁰C) Diesel (300⁰C) Kerosene (200⁰C) Gasoline (petrol) (150⁰C) Petroleum gas (20⁰C) Can be used as fuels May be further processed to make petrochemicals (chemicals made from natural gas and oil)

BOILING POINTS OF ALKANES

Effect of chain length
 Increase in chain length
 More points of contact between molecules
 More van der Waals' forces between the molecules
 More energy (higher temperature) to separate the molecules Effect of branching
 A branched isomer has a lower boiling point than the unbranched isomer
 Branched alkanes have fewer points of contact between molecules
 Less van der Waals' forces between molecules
 Branched molecules cannot get as close to each other as unbranched ones
 Intermolecular forces decreases between molecules
 Less energy required to separate the molecules

USES OF ALKANES



Methane is used for cooking Propane and butane are LPGs LPGs are used as fuels in barbecues etc. Octane is present in petrol

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