Since carbon has four electrons in its valence shell, it needs four more electrons to complete its octet. Therefore, it is a tetravalent element.
In order to complete its octet i.e., to attain its noble gas configuration and to stabilize itself, carbon can:
Either lose four electrons to form C4+ or gain four electrons to form C4−. This, however, requires a lot of energy and would make the system unstable. Therefore, carbon completes its octet by sharing its four electrons with the other carbon atoms or with atoms of other elements. The bonds that are formed by sharing electrons are known as covalent bonds. Covalently bonded molecules have weak intermolecular forces, but intramolecular forces are strong.
2.Allotropic Forms of Carbon Carbon is the versatile element present in food, clothes, medicines, papers, etc. In addition, all living structures are carbon based. The earth’s crust has only 0.02% carbon in the form of minerals and the atmosphere has 0.03% carbon dioxide. In spite of the small amount of carbon available in nature, the importance of carbon is immense.
3.Allotropy: The phenomenon due to which an element exhibits different physical forms is called allotropy. Reasons for allotropy are different arrangement of atoms in each allotrope, different methods by which each allotrope is prepared, and different amount of energy associated in the formation of each allotrope. Carbon is considered to have two main kinds of allotropes i.e., crystalline and amorphous.
Well known allotropes of carbon are: 1. Diamond 2. Graphite 3. Buckminsterfullerene
4. Crystalline forms of carbon Diamond Crystal structure: In diamond, each atom of carbon of the given crystal unit is surrounded by four other carbon atoms, which are joined by covalent bonds,
The diamond crystal is a compact structure in which atoms of a single unit lie in different planes. Thus, the atoms cannot slip because of their different positions in different planes and hence, diamond is the hardest naturally occurring substance.
5.Physical properties:
The physical properties of diamond are:
It is the hardest naturally occurring substance.
Pure diamond is colourless, transparent, but brittle solid.
It is chemically inert under ordinary conditions as there are no free electrons available.
It is a good conductor of heat but is does not conduct electricity.
Its refractive index is 2.42.
Its specific gravity is 3.52.
It is the densest form of carbon, its density being 3.5.
It is transparent to X-rays, ultraviolet rays, and visible light rays.
6. Chemical properties:
The chemical properties of diamond are:
Action of air or oxygen: When diamond is heated in air, it catches fire at 800oC. It does not leave behind any ash and therefore, it is the purest form of carbon.
Action of sodium carbonate: When diamond is heated very strongly with solid sodium carbonate, it reacts to form sodium oxide and carbon monoxide.
7. Uses: The various uses of diamonds are:
They are generally used for making ornaments.
They are used for cutting glass as well as diamonds.
They are used for making dies for drawing wires.
They are used as bearings in watches.
They are used in making laser beam in electronics.
8.Graphite Crystal structure:
In graphite, atoms of a single crystal are arranged in a hexagonal ring in a single plane. The bonds between the carbon atoms of two single crystals in the parallel planes are weak. Thus, one plane can easily slide over another plane by applying pressure. This is why graphite is soft and can be used as a lubricant.
9.Physical properties:
The physical properties of graphite are:
It is dark grey solid, having lustre.
It is a very good conductor of heat and electricity.
It is opaque to light.
Its specific gravity is 2.2.
It is opaque to X-rays, ultraviolet rays, and visible light rays.
10.Chemical properties:
The chemical properties of graphite are:
Action of air or oxygen: Graphite does not burn in air. However, if graphite is heated in air, then it catches fire at 700oC and forms a mixture of carbon dioxide and carbon monoxide.
Action of sodium carbonate: Like diamond, graphite also form sodium oxide and carbon monoxide when heated with solid sodium carbonate.
11.Uses: The various uses of graphite are:
It is used in making lead pencils. It is used in making electrodes. It is used as a dry lubricant. It is used as a moderator in a nuclear reactor.
12.Buckminsterfullerene:
It is the third and the most recently discovered allotrope of carbon. Buckminsterfullerene is a cluster of sixty carbon atoms arranged in the form of a football. It is named after the American architect Buckminster Fuller, as it resembled the geodesic dome designed by him. Since it contains sixty carbon atoms, its chemical formula is C60.
13.Amorphous Forms of Carbon
What is an amorphous solid?
An amorphous solid is a non-crystalline solid with no well-defined ordered structure. Some amorphous forms of carbon:
Charcoal: It is produced from the bones of animals, combustion of wood etc.
Lampblack or soot: It is produced from the incomplete combustion of hydrocarbons.
14. Do you know why carbon is a part of so many compounds?
Which properties of carbon help it to be a part of so many compounds? Here, we will try to find the answers to these questions. The most important property of carbon that allows it to be a part of so many compounds is catenation. Catenation is the ability of an element to combine with itself through covalent bonds. Carbon has a unique ability to combine with other atoms of carbon to form long chains and rings. Carbon forms very strong bonds with itself. Hence, the chains and rings formed by carbon through catenation are very stable. Thus, these chains and rings are not only long, but also very stable. This is because carbon can form strong single, double, and triple bonds with other atoms of carbon. This can give rise to branches, chains, and rings
15. Apart from carbon, a very few elements display the property of catenation so extensively. Silicon can join with other atoms of silicon, but the maximum length of the chains that can be obtained in the case of silicon is limited to seven or eight atoms. In addition, the compounds formed by silicon by catenation are not very stable.
16.Saturated and Unsaturated Compounds Saturated compounds: The compounds of carbon having only single bonds between the carbon atoms are called saturated compounds. For example, a molecule of ethane (C2H6) contains one single bond between the carbon atoms.
17.Unsaturated compounds: The compounds of carbon having double and triple bonds between the carbon atoms are called unsaturated compounds. For example, ethene is an unsaturated compound containing one double bond between the carbon atoms.
18.Organic compounds and Homologous Compounds The number of carbon compounds is so vast that there is one branch of chemistry dedicated only to the study of carbon and its compounds. This branch is known as organic chemistry. The compounds of carbon having only single bonds between the carbon atoms are called saturated compounds and those that contain a double or a triple bond between any two carbon atoms are known as unsaturated compounds. For example, a molecule of propane (C3H8) contains two single bonds between the carbon atoms.
19.There are two main groups of hydrocarbons:
20.Aliphatic hydrocarbons:
They are derived from fossil fuels. They are those hydrocarbons which possess straight chain or branched chain structures.
They are grouped as:
21.Alkanes: The general formula of alkanes is CnH(2n+2), n = number of carbon atoms. They contain only single bonds between all the carbon atoms present in a given molecule of an alkane. For example, methane (CH4), ethane (C2H6) etc.
22.Alkenes: The general formula of alkenes is CnH2n, where n = number of carbon atoms They contain at least one carbon − carbon double bond. For example, ethene (C2H4), propene (C3H6) etc.
23. Alkynes: The general formula of alkynes is CnH(2n−2), where n = number of carbon atoms They contain at least one carbon-carbon triple bond. For example, ethyne (C2H2), propyne (C3H4) etc.
24.Alicyclic saturated hydrocarbons: They are those saturated hydrocarbons in which the carbon atoms form a ring. Their general formula is similar to that of alkenes (CnH2n). For example, cyclopropane
25.Aromatic hydrocarbons: Members of this group have a characteristic odour. First recognised aromatic hydrocarbon is Benzene (C6H6) Benzene is a good organic solvent, which is used in the preparation of dyes, medicines, perfumes etc. Consider, a molecule of butane (C4H10) contains three single bond
26.these structures have carbon atoms linked to each other in a repeated manner. Such structures are called Chain structures and compounds exhibiting such structures are known as aliphatic compounds.
27.Carbon atoms in a molecule cannot only be linked in a chain or branch form, but these can also be arranged in a ring. For example, benzene, cyclohexane etc. Benzene is a six-member ring that contains three double bonds. Thus, it is an unsaturated hydrocarbon. On the other hand, cyclohexane has only single bonds. Hence, it is a saturated compound.
28.However, the organic compounds which contain at least one benzene ring are known as aromatic compounds. For example, benzene, toluene, xylenes etc.
29.Carbon not only bonds to carbon and hydrogen, but it can also bond to other atoms like halogens (Br, Cl, I, F), nitrogen, oxygen etc. Sometimes, the hydrogen attached to a carbon in a hydrocarbon can also be replaced by another atom. In such cases, the replacing atom is called a heteroatom. A single atom or a group of atoms, which on bonding with a hydrocarbon, modifies the properties of the compound, is referred to as a functional group.
30. it was noticed that the properties of CH3OH, C2H5OH, and C3H7OH are very similar. Can you tell why? This is because they form a part of the Homologous series.
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