American School of Creative Science
Science Department
Revision Sheet
(Hydrocarbons)
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The simplest organic molecules are pure hydrocarbons which contain only hydrogen and carbon.
Hydrocarbons are compounds that are made up of carbon and hydrogen atoms ONLY.
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A homologous series is a family of hydrocarbons with similar chemical properties who share the
same general formula differing from the successive member by CH2.We will look at three
hydrocarbon series: alkanes, alkenes, and the cycloalkanes.
saturated hydrocarbon is a hydrocarbon in which there is only a single bond between Carbon
atoms in the hydrocarbon chain. For example, Alkane. An unsaturated hydrocarbon is a
hydrocarbon in which there is a double or triple bond between any adjacent Carbon atoms. For
example, alkenes & alkynes.
Alkanes are the simplest hydrocarbons with no functional group. With the general
formula CnH2n+2
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They are made up of carbon and hydrogen atoms bonded to each other with single covalent
bonds.
Physical Properties of Alkanes:
 Polarity of alkanes: Alkanes are non-polar in nature because of same electro negatives of carbon
atoms.
 Boiling point: Because of non-polar character they have low boiling point. The boiling points
increase with increase in the number of carbon atoms due to increase in Vander wall forces of
attraction. However, with increase in branching the surface area decreases and hence, Vander wall
force decreases and hence the boiling point decreases. For example: CH3 CH2CH2 CH3 butane
has more boiling point then 2 methyl propane.
 Solubility: We know Hydrocarbons are non-polar and we also know like dissolve like So they are
not soluble in H2O but soluble in organic solvents.
Alkenes:
They are the hydrocarbons with C = C (double bond) with one bond and other π bond. o Their
General formula Cn H2n.
Physical Properties of Alkenes:
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Boiling Point: They show regular graduation. With increase in Carbon atoms, Vander wall
force increases so, boiling point also increases. Boiling point decreases with increase in
branching. As surface area reduces Vander wall force decreases, therefore boiling point also
decrease.
Solubility: Alkenes have greater solubility then alkanes. Solubility increases with increase in
C atoms.
Alkynes:
In this triple bond is present between carbon atoms. The general formula involved is CnH2n -2. The
lowest member of alkynes is ethyne.
Physical Properties of Alkynes:
 Solubility: They are weekly polar in nature and not soluble in H2O but soluble in
organic solvents.
 Melting point and boiling point: Because of triple bond they have higher melting point
and boiling point. With increase in number of carbon atoms the boiling point
increases. With increase in branching the boiling point decreases.
Cycloalkanes
are cyclic hydrocarbons, meaning that the carbons of the molecule are arranged in the form of a ring.
Cycloalkanes are also saturated, meaning that all the carbons atoms that make up the ring are single
bonded to other atoms (no double or triple bonds). The general formula for a cycloalkane is CnH2n
For simplicity, cycloalkane molecules can be drawn in the form of skeletal structures in which each
intersection between two lines is assumed to have a carbon atom with its corresponding number of
hydrogens.
same as
same as
An alkyl group is formed by removing one hydrogen from the alkane chain. The removal of this
hydrogen results in a stem change from -ane to -yl to indicate an alkyl group. The removal of a
hydrogen from methane, CH4, creates a methyl group -CH3.
IUPAC NOMENCLATURE of ALKANES
1. Identify the longest continuous carbon chain as the parent chain. This chain determines the
parent name (or last name) of the alkane.
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If there are two choices of the same length, then the parent chain is the longest chain with
the greatest number of “branches”. The term substituent will be used from now on as the
official name for “branch”.
2. Number the chain beginning at the end that is closest to any substituents, thus ensuring the
lowest possible numbers for the positions of substituents.
3. Use these numbers to designate the location of the substituent groups, whose names are
obtained by changing the “-ane” suffix to “-yl“.
The substituents derived from alkane are also called alkyl groups.
If an alkyl substituent group appears more than once, use the prefixes di, tri, tetra, penta, and hexa
(meaning 2, 3, 4, 5, and 6 respectively) for each type of alkyl group.
4. List the substituent groups alphabetically
5. Write the name as a single word. Numbers are separated from letters by “-“; numbers are
separated by “,”.
Alkane Naming Examples:
IUPAC NOMENCLATURE of CYCLOALKANES
1. The parent name is “cycloalkane”.
2. Number the ring to provide the lowest possible numbering sequence (when two such sequences
are possible, cite substituents in alphabetical order, and the No. 1 position is given to the first
cited substituent).
Example:
3. When both the ring and chain are included in the structure, compare the number of carbons in the
ring vs the chain and select the one with more carbons as the parent structure; the other is treated as a
substituent.
Example:
Lab (Distillation)
Distillation: A method of separating mixtures based on differences in their volatilities in a boiling
liquid mixture. The components in a sample mixture are vaporized by the application of heat and then
immediately cooled by the action of cold water in a condenser.
Two Types of distillation : Fractional and Simple distillation.
Fractional distillation is the separation of a mixture into its component parts, or fractions. Chemical
compounds are separated by heating them to a temperature at which one or more fractions of the
mixture will vaporize. So when the mixture is heated, the substance with lower boiling point starts to
boil first and convert into vapors. It is useful for separating ethanol from a mixture of ethanol and
water, and for separating different fractions from crude oil.
What is simple distillation and how does it work?
Simple distillation enables a liquid to be separated from a solution. The solution is heated until the
solution with the lowest boiling point starts to evaporate. The vapor is cooled and it condenses (turns
back into a liquid). This liquid can be collected, leaving the rest of the solution back in the flask. For
example separating pure water from sea water