case /data -based [Che-4M]

Question 14 Marks

Carbon is a versatile element that forms the basis of all living organisms and many of the things we use. A large variety of compounds is formed because of its tetravalency. Compounds of carbon are formed with oxygen, hydrogen, nitrogen, sulphur, chlorine and many other elements.
Answer the following questions:
a. What are hydrocarbons?
b. List two properties by virtue of which carbon can form a large number of compounds.
c. Write the formula of the functional group present in (1) aldehydes, and (2) ketones. Write chemical equation for the reaction that occurs between ethanoic acid and ethanol in the presence of a catalyst.
OR
What are structural isomers? Write the structures of two isomers of butane $\left(\mathrm{C}_{4} \mathrm{H}_{10}\right)$.

Answer

a. Compounds formed by carbon and hydrogen only.
b. Tetravalency and Catenation

OR
Compounds with identical molecular formula but different structures
Two isomers of butane $\mathrm{C}_{4} \mathrm{H}_{10}$

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Question 24 Marks

As neutral atom carbon has electronic configuration $\underset{2,}{K} \underset{4}{L}$. To gain inert gas configuration carbon can either donate 4 valence electrons (helium gas configuration) or gain 4 electrons (neon gas configuration), but it cannot do so. To acquire inert gas configuration carbon can only share its 4 valence electrons with other atoms forming covalent bonds. A covalent bond can be defined as a chemical bond formed between two atoms by mutual sharing of valence electrons so that each atom acquires the stable electronic configuration of the nearest noble gas. The concept of covalent bonds was given by Langmuir and Lewis to explain bonding in non-ionic compounds. The covalent bonds are of three types. If each atom contributes one electron, the covalent bond formed is called a single covalent bond and is represented by a single line (-) and if each atom contributes two electrons, the covalent bond formed is called a double bond and is represented by a double line ( $=$ ) and if each atom contributes three electrons, the covalent bond formed is called a triple bond and is represented by a triple line ( $\equiv$ ).
i. Define Catenation.
ii. What are name given for carbon atoms linked with single, double, triple bond?
iii. Define Valency and write two examples of molecules containing double bond.
OR
Draw the electron dot structure for $\mathrm{Cl}_{2}$ molecule.

Answer

i. Catenation can be defined as the self-linking property of atoms of an element through a covalent bond so as to form large chain, rings, branched chain of varying length.
ii. Alkanes- carbon atoms connected by single bond.Alkenes- carbon atoms connected by double bond.
Alkyne- Carbon atoms connected by triple bond.
iii. The combining power of an element with other atom to form chemical bond is called valency.Examples of molecules having double bond are
Carbon dioxide( $\mathrm{CO}_{2}$ ),Sulphur dioxide( $\mathrm{SO}_{2}$ )
$\mathrm{O}=\mathrm{C}=\mathrm{O}, \mathrm{O}=\mathrm{S}=\mathrm{O}$

OR
In chlorine molecule, both chlorine atoms contribute one electron and thus share single electron pair to form single covalent bond. As shared pair is shared by both atoms, they acquire inert gas configuration of argon atom in valence shell.

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Science case /data -based [Che-4M]

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