Carbon Chemistry Notes PDF - Class X

Birla Public School, Doha- Qatar Science- Chemistry. Class X: Ch- 4- Carbon and its compounds- Notes Part-1 Introduction  Carbon is the 6th element in the Modern Periodic Table.  It belongs to the...

Birla Public School, Doha- Qatar Science- Chemistry. Class X: Ch- 4- Carbon and its compounds- Notes Part-1 Introduction  Carbon is the 6th element in the Modern Periodic Table.  It belongs to the second period and the 14th group of the MPT.  Its E.C is 2, 4 and valency is 4, ie, it is a tetravalent atom. Bonding in Carbon. Since carbon has tetravalency, it can either loss or gain 4 electrons to complete its octet. But this arises certain problems. If it were to gain or lose electrons-  It could gain 4 electrons forming C4- anion. But it would be difficult for the nucleus with six protons to hold on to 10 electrons- 4 extra electrons gained.  It could lose 4 electrons forming C4+ cation. But it would require a large amount of energy to remove 4 electrons leaving behind a carbon cation with 6 protons holding on to just 2 electrons.  Carbon overcomes this problem by sharing its valence electrons with other atoms of carbon or with atoms of other elements.  Hence Carbon forms covalent bonding.  Covalent bond is a bond formed by sharing valence electrons with atoms of the same or different types.  It can generally happen between non- metal atoms.  The compound formed by this bond is called covalent compound and it is molecule in nature. Carbon form covalent bonds. Formation of covalent bond: Covalent bond formation involves sharing of electrons between bonding atoms which may be either same or different.  Covalency : The number of electrons contributed by an atom for sharing is known as its covalency. Formation of Covalent Bond- Types and Examples with Electron dot structure. Depends upon the number of electrons shared between the atoms, covalent bond can be divided as:-  Single Covalent Bond- When a single pair of electrons (2 e-, 1 from each atom) are shared between two atoms in a molecule, the bond is called single covalent bond. Eg: H2, F2, Cl2, CH4 etc. (https://youtu.be/oqcVYejHpw8)  Double Covalent Bond- When two pairs of electrons (4 e-, 2 from each atom) are shared between two atoms in a molecule, the bond is called double covalent bond. Eg: O2, CO2, C2H4 etc.  Triple Covalent Bond- When three pairs of electrons (6 e-, 3 from each atom) are shared between two atoms in a molecule, the bond is called triple covalent bond. Eg: N2, C2H2, etc. Structure of Sulphur molecule- S8 Characteristics of covalent compounds: (i) These compounds are molecular in nature (i.e. they exist as single molecules) (ii) These are generally insoluble in water and soluble in benzene, kerosene and petrol etc (Organic solvents). (iii) These compounds are poor conductor of electricity since they cannot form any charged particles or ions. (iv) They have strong bonds within the molecule, but the inter- molecular forces of attraction are very small. Because of this, they have low melting and boiling points. (v) They are usually liquids or gases, but some of them are solids. Occurrence of Carbon  Carbon is found in Free State as well as in compound state in the Nature. In Free State, it is found as diamond, graphite and Buckminster fullerene. These are called the allotropes of carbon. These are also the crystalline forms of carbon. Carbon also exists in free form as amorphous solids which do not have crystalline shape such as coal, coke etc.  In compound state, it is found as carbon dioxide and carbon monoxide in the atmosphere, as carbonates in minerals, in the exo and endoskeleton of many organisms. Allotropy The phenomenon in which the elements exists in different crystalline forms in the same physical state with similar chemical properties but different physical properties is called allotropy. The various forms are called allotropes. They have similar chemical properties as they are of same atoms and the difference in physical properties is due to the difference in the structural arrangements of the atoms in the molecule. Diamond and graphite are two common allotropes of carbon and Buckministerfullerene is the new one discovered recently. We can show that they are made of the same atoms by burning each of them separately to form CO2 gas. Formation of diamond naturally: Based on the study of diamonds and their inclusions, most diamonds grow from carbon-bearing fluids in the mantle as they migrate and flow through the cracks in rocks. As the fluid percolates, changes in pressure, temperature or composition can cause carbon to crystallize out of the fluid into a solid form diamond. While inclusions can give insight into the processes of diamond formation, they can also enable us to constrain the age of a diamond. Formation of diamond artificially: Diamond can be made artificially by subjecting pure carbon to very high pressure and temperature. These are called synthetic diamonds which are smaller than the natural diamond but are otherwise indistinguishable from natural ones. Differences between Diamond and Graphite Parameters Diamond Graphite Structure:- Each carbon atom is bonded Each carbon atom is bonded to 4 other carbon atoms to 3 other carbon atoms in forming a rigid 3D structure the same plane forming a of a regular tetrahedron hexagonal arrangement in shape. All the 4 valence layer form. The layers are electrons are used in attracted each other by weak bonding. force of attraction. Actually only 3 valence electrons are used in bonding Appearance Colourless, transparent Greyish, black, opaque  having extra ordinary substance brilliance. Nature and strength Hard and rigid due to strong Lighter, soft and slippery due of Bond covalent bond to weak covalent bond Electrical Do not conduct electricity as Good conductor of electricity conductivity there is no free electrons due to free electrons due to its structure. Density, Melting point It is denser and has high It has low density and melting point due to the rigid melting point structure. It needs large energy to break the strong covalent bond between the atoms in the molecule. So melting point is high. Uses Used as glass cutter, rock Used as electrodes, pencil borers, in jewellery leads, lubricant etc. Diamond structure- Graphite structure- Buckminster fullerene: - It contains clusters of 60 carbon atoms joined together to form spherical molecules. So, its formula is C60. It is a football shaped spherical molecule in which 60 carbon atoms are arranged in interlocking hexagonal and pentagonal rings of carbon atoms. There are 20 hexagons and 12 pentagons of carbon atoms in one molecule of Buckminster fullerene. It is a dark (black) solid at room temperature. It is neither very hard nor soft. It is used as a conductor, in carbon nanotubes and in biomedical field. Its structure is as follows: https://youtu.be/K4FcQ8tPpKQ (Manocha academy) Versatile nature of carbon The number of carbon compounds are very large. The nature of covalent bond enables carbon to form a large number of compounds. Two factors responsible for this are:- a) Catenation:- The property of self-combination of carbon atoms to form long chain, branched chain or cyclic compounds, compounds with single, double or triple covalent bonds and also to bond with other atoms is called catenation. No other element exhibits the property of catenation to the extent seen in carbon compounds. Silicon is another atom that can show catenation, but it forms compounds with hydrogen which have chains upto 7 or 8 atoms. Carbon atoms form strong bonds among themselves and with other atoms makes the carbon compounds exceptionally stable. b) Tetravalency of carbon:- Since it is a tetravalent atom and also small sized atom, it is capable of bonding with 4 other carbon atoms or other atoms and these bonds are very strong. Prepared by: Sheri Symon