Class 10 Science Chapter 4 Carbon and its Compounds Important Questions

Ans: Covalent compounds have low melting and boiling points because the forces of attraction between molecules of covalent compounds are very weak. On applying a small amount of heat these molecular forces break.

Ans: (i) C_2H_4 belongs to alkene series having a general formula, C_nH_{2n} .Thus, next homologue will be C_3H_{2×3} = C_3H_6 ‍(ii) C4H6 belongs to the alkyne series having general formula, C_nH_{2n-2}. Thus, next homologue will be C_5H_2×5-2 = C_5H_8

Ans: Ionic compounds are formed either by gaining or losing electrons from the outermost shells, but carbon which has four electrons in its outermost shell cannot form ionic bonds because 1. If carbon forms ionic bonds by gaining four electrons to attain a noble gas configuration then it would be difficult for six protons in the nucleus to hold ten electrons. 2. If carbon forms ionic bonds by loss of four electrons then it would require a lot of energy to remove these electrons from the outermost shell. Due to these reasons carbon forms covalent bonds by sharing the valence electrons. Type of bonds formed in ionic compounds are called electrovalent bonds and the type of bonds formed in carbon compounds are called covalent bonds.

Ans:(i) As carbon has four valence electrons and it can neither lose nor gain our electrons thus, it attains noble gas configuration only by sharing of electrons. I bus, it forms covalent compounds. (ii) In diamond, each carbon atom is bonded to four other carbon atoms forming a rigid three-dimensional structure. This makes diamond the hardest known substance. Thus, it has a high melting point. (iii) In graphite, each carbon atom is bonded to three other carbon atoms by covalent bonds in the same plane giving a hexagonal array. Thus, only three valence electrons are used for bond formation and hence, the fourth valence electron is free to move. As a result, graphite is a good conductor of electricity.

Ans: Covalent bonds are those bonds which are formed by sharing of the valence electrons between two atoms. Electron dot structure of methane is shown in the figure.