Q) Why carbon doesn’t gain or lose electrons?
-> Carbon atom does not gain electron and form C4- anion because it would be difficult for the
nucleus with six proton to hold
10 electrons.
carbon atom also does not loose electrons and form C4+ cation because it would require a large
amount of energy to remove four electrons from carbon atom. Hence, carbon does not gain or
lose electrons.
* Note:- To overcome this problem, carbon share their valence electrons and formed covalent
bond with other atoms of carbon or another element.
Properties of covalent compounds
(i) Covalent compounds usually have low melting points except Silica (SiO2) and Diamond that
have a high melting point.
(ii) Covalent compounds have low boiling points because of presence of weak force of attraction
between their atoms and this force is called Van der wall force.
(iii) Covalent compounds are usually gases and liquids but some are also solid.
(iv) Generally covalent compounds are poor conductor of heat and electricity but some are good
conductor of electricity such as graphite.
(v) Generally covalent compounds are insoluble in water and other polar solvent but soluble in
organic solvents like benzene (C6H6), toluene (C6H6-CH3), etc.
Note:- Silica or Quartz is one of the hardest and second most common materials in the
Earth's crust.
It is formed when silicon is exposed to oxygen.
Test for carbon
-> Burn the material in the presence of air and if it gives CO2 then it has a carbon unit.
* Allotrope- The compounds which are made up of same elements but their structure are
different called allotrope.
As a result their properties are different from each other.
* Amorphous carbons are made of graphite particles.
Diamond
-> In diamond, each C-atom is bonded to four other C-atoms.
As a result, it formed a rigid 3D structure.
* Its structure is tetrahedral.
* It is the hardest natural substance.
* Due to presence of a large 3D network of C-C covalent bond, Diamond is very hard and
have high melting point i.e. almost 4027 0 C.
* Diamond is a bad conductor of electricity due to absence of free electrons in its structure
because all the four electrons are utilised in making covalent bonds.
* It shines in presence of light because when light falls on diamond then light rays get trapped in
its
interior faces and perform total internal reflection (
TIR ).
As a result diamond are colourless and transparent.
Uses of diamonds
-> Due to its hardness, it is used for making cutting and drilling tools.
-> It is used for cutting glasses.
-> Due to its extra ordinary shine, it is used for making jewellery.
-> It is used in surgical instrument to remove the cataract from eyes.
-> It is used for making component of industrial cutting and polishing tools.
Note->
It can be synthesized when pure carbon kept at very high temperature
and pressure.
The synthetics diamond are small as compared to natural diamonds.
Graphite
-> In graphite, each C-atom is bonded to three other C-atoms.
As a result, it formed a flat hexagonal ring like structure.
* The various layer of C atom is graphite are joined by weak van der wall force, not covalent bond.
As a result they can slide over each other.
* Graphite is a good conductor of electricity because it has free electrons in its structure
which conduct electricity from one side to another side of graphite.
* It also has very high melting point just like diamond.
Uses
-> Due to its slippery nature, powdered graphite is used as lubricant for fast moving parts
of machinery.
-> Due to good conductor of electricity, it is used for making carbon electrodes or
graphite electrodes in dry cell.
-> It is also used for making pencil leads because graphite is black in colour and mark black
lines on paper.
-> It is also used for making black paints.
-> Graphite has the ability to absorb fast-moving neutrons, thus, it is used in nuclear reactors
to control the speed of the nuclear fission reaction.
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