CARBON COMPOUND
Carbon is an element. The symbol of carbon
is C. It is a non-metal. The
name carbon is derived from the Latin word 'carbo' which means 'coal'. The amount of
carbon present in the earth's crust and atmosphere is very small. the earth's
crust contains only 0.02% carbon and the atmosphere has only 0.03% of carbon
dioxide gas. all
the living things, plants and animals, are made up of carbon based compounds
which are called organic compounds. Thus, carbon element is present in all
living things.
Occurrence
of Carbon
Carbon occurs in nature in 'free state' (as element) as well as
in the 'combined state'
In
free state,
carbon occurs in nature mainly in two forms: diamond and graphite.
In
the combined state, carbon occurs in nature in the form of compounds such as :
(i)
Carbon dioxide gas in air
(ii)
Carbonates (like limestone, marble and chalk)
(iii) Fossil fuels like coal,
petroleum and natural gas
The various
physical forms in which an element can exist are called allotropes of the
element.
Three
allotropes of carbon are
1. Diamond
·
Diamond is a colourless transparent substance having
extraordinary brilliance (chamak)
·
It is
the known hardest natural
substance.
Reason : The rigid structure of diamond makes it a very hard
substance.
·
Diamond does not conduct electricity.
Reason
:
there are 'no free electrons' in a diamond crystal, it does not
conduct electricity.
·
The melting point of diamond is also very high, being more
than 3500°C.
Reason : This is because a lot of heat energy is required to break
the network of strong covalent bonds in the diamond crystal.
·
If we burn diamond in oxygen,
then only carbon dioxide gas is formed and nothing is left behind. This shows
that diamond is
made up of carbon only.
How
identify : The
carbon dioxide formed by burning graphite can turn lime water milky.
·
The
carbon dioxide formed by burning diamond
Uses of Diamond
·
Diamonds are used in cutting instruments like glass cutters
·
Diamonds are used for making jewellery
·
Sharp-edged diamonds are used by eye-surgeons as a tool to
remove cataract from eyes
 |
| Diamond structure |
2. Graphite
·
Graphite is a greyish-black opaque substance
·
Graphite is lighter than diamond.
·
Graphite is soft and slippery to touch.
Reason :
the various layers of carbon atoms in graphite are joined by weak forces, they
can slide over one another.
·
Graphite conducts electricity.
Reason : Due to the 'presence of free electrons' in a graphite
·
The carbon dioxide formed by burning graphite
·
If we burn graphite in oxygen, then only carbon dioxide gas is
formed and nothing is left behind. This shows that graphite is made
up of carbon only.
·
The carbon dioxide formed by burning graphite
Uses
of Graphite
·
powdered graphite is used as a lubricant for the fast moving
parts of machinery.
·
graphite is used for making carbon electrodes or graphite
electrodes in dry cells and electric arcs.
·
Graphite is used for making the cores of our pencils called
'pencil leads' and black paints
 |
| Graphite structure |
1. Buckminsterfullerene
·
Buckminsterfullerene is an allotrope of carbon containing
clusters of 60 carbon atoms joined together to form spherical molecules.
·
There are twenty hexagons and twelve pentagons of carbon
atoms in one molecule of buckminsterfullerene.
·
Buckminsterfullerene is a dark solid at room temperature.
·
If we burn buckminsterfullerene in oxygen, then only carbon dioxide gas is
formed and nothing is left behind. This shows that buckminsterfullerene is made
up of carbon only.
 |
| Buckminsterfullerene structure |
ORGANIC COMPOUNDS
·
The compounds of carbon are known as organic compounds.
·
Organic compounds are covalent compounds having low melting
points and boiling points. Most of the carbon Compounds are non-conductors of
electricity. Organic compounds occur in all living things like plants and
animals.
·
Carbon monoxide and carbon dioxide, carbonates, hydrogen
carbonates and carbides are also carbon compounds but They are not considered
to be organic compounds.
Reason
: This is because their properties are very different from those of the common
organic compounds.
·
The study of carbon compounds is called organic chemistry.
·
There are more than 5 million organic compound.
Catenation (self-linking)(Figure)
: carbon atoms can link with one another by
means of covalent bonds to form long chains (or rings) of carbon atoms. This
property of carbon compound is known as catenation or self linking. This
property of carbon compound is responsible for existence of a large number of
organic compounds.
Tetravalency (four
valency) : Valency of carbon element is 4 which is quite large and responsible for
existence of a large number of organic compounds
HYDROCARBONS
A compound made
up of hydrogen and carbon only is called hydrocarbon (Hydrogen + Carbon =
Hydrocarbon). The most important natural source of hydrocarbons is petroleum
(or crude oil)
Types of
Hydrocarbons. Hydrocarbons are of two types :
1.
Saturated hydrocarbons
and 2. Unsaturated hydrocarbons.
Saturated Hydrocarbons (Alkanes):
·
A hydrocarbon in which the carbon atoms are connected by only single bonds is
called a saturated hydrocarbon.
·
An alkane is a hydrocarbon in which the carbon atoms are connected by
only single covalent bonds (There are no double or triple bonds in an alkane). -C-C-
·
The general formula of saturated hydrocarbons or alkanes is
CnH2n +2 where n is the number of carbon atoms in
one molecule of the alkane.
·
Put n = 1,2,3… we get
Unsaturated Hydrocarbons (Alkenes and Alkynes)
Unsaturated
hydrocarbons are of two types :
(i)
alkenes
and (ii) alkynes.
(i)Alkenes
·
An unsaturated hydrocarbon in which the two carbon atoms are
connected by a double bond is called an alkene. 
·
The general formula of an alkene is CnH2n where n
is the number of carbon atoms in its one molecule.
·
The Value of n can not one because alkene compound need at least two carbon atom to form double
bond between C to C
·
Examples
(ii)
Alkynes :
·
An unsaturated hydrocarbon in which the two carbon atoms are
connected by a triple bond is called an alkyne.
·
The general formula of alkynes is CnH2n where n is the number
of carbon atoms in one molecule of the alkyne.
·
When n = 2 we get C2H 2 which is known
as acetylene or ethyne.
Examples
Alkyl Groups
·
The group formed by
the removal of one hydrogen
atom from an alkane molecule is
called an alkyl group.
·
The general
formula of an alkyl group is CnH2n +1
where n is the number of carbon
atoms
·
Examples
of alkyl group are methyl group (CH3-) and ethyl
group (C2H5-
).
Cyclic compound :
Saturated cyclic compound
Cyclohexane
C6H12
Electron-dot
structure of cyclohexane has been obtained by putting two electron dots in
place of every single bond in its structural
 |
| Cyclohexane C6H12 |
The molecular
formula of cyclopentane is
C5H10. Cyclopentane has
5 carbon atoms in the form
of
a pentagonal ring
which are connected by single bonds.
 |
| Cyclopentane C5H10 |
Benzene is
C6H6
Electron-dot
structure of benzene has been obtained by putting two electron dots in
place of every single bond and four electron
dots in place of every double bond in its structural formula.
 |
| Benzene C6H6 |
Isomers
The organic
compounds having the same molecular formula
but different structures are known as isomers.
Isomerism is
possible only with hydrocarbons having 4 or more carbon atoms
no isomerism is
possible in methane, ethane and propane because they contain only one, two or
three carbon atoms respectively
Example n-butane
and iso-butane
Compound Number of Isomers
butane (C4H10) 2
pentane (C5H12)
3
hexane (C6H14) 5
This comment has been removed by the author.
ReplyDeletebakwaas tatti jese ekdum maa chuda lo is se acccha
ReplyDelete