Very Short Answers
Question. What would be the electron dot structure of carbon dioxide which has the formula CO2?
Answer: The atomic number (Z) for carbon is six and its electronic configuration is 2, 4. Carbon has four valence electrons.
Each oxygen atom (Z = 8) has six valence electrons (2, 6). In order to complete its octet, the carbon atom shares its four valence electrons with the four electrons of the two
oxygen atoms as follows :
Thus, in carbon dioxide molecule, the carbon atom is linked to two oxygen atoms by two shared pairs of electrons resulting in double bonds on either sides. Both carbon and oxygen
atoms complete their octet as a result of electron sharing.
Question. Why is homologous series of carbon compounds so called? Write the chemical formula of two consecutive members of any homologous series and state the part of these compounds that determines their (i) physical and (ii) chemical properties.
Answer: A homologous series is the family of organic compounds having the same functional group, similar chemical properties but the successive (adjacent) members of the series are differ by a CH2 unit or 14 mass units.
Consecutive members of the homologous series of alcohols are :
CH3 OH ] They differ by CH unit.
The physical properties are determined by alkyl group/ hydrocarbon part/part other than the functional group.
The chemical properties are determined by functional group such as —OH group.
Question. Define isomerism. Write down the structures and names of isomers of butane.
Answer: Two or more compounds having same molecular formula but different structural arrangements of atoms in their molecules are called isomers. This phenomenon is called
Question. An element X has a proton number of 15, while element Y has a proton number of 17. Draw a ‘dot-and-cross’ diagram to show all electrons in a molecule formed from elements X and Y.
Answer: Electronic configuration of X : 2, 8, 5 Atom X contributes three electrons for sharing.
Electronic configuration of Y : 2, 8, 7 Each atom of Y contributes one electron for sharing.
Therefore, three atoms of Y contribute three electrons for sharing.
One atom of X will share three pairs of electrons with three atoms of Y to achieve the noble gas configuration.
Both atoms X and Y achieve the electronic configuration of argon (2, 8, 8).
Question. (a) What type of bond holds the two chlorine atoms together in a chlorine molecule?
(b) Briefly describe how this bond is formed.
(c) Draw a ‘dot-and-cross‘ diagram to show the bonding in a chlorine molecule.
Answer: (a) Covalent bond
(b) The two chlorine atoms share one pair of electrons, so that both atoms achieve a noble gas configuration.
Question. The diagram shows one layer of carbon atoms in the structure of graphite:
(a) Identify the types of bonding in graphite.
(b) Which property of graphite makes it suitable for use as a dry lubricant? Explain your answer.
Answer: (a) Covalent bonds between carbon atoms in each layer and van der Waals’ forces between the layers of carbon atoms.
(b) Graphite is soft. The layers of carbon atoms can slide and glide over each other because the weak van der Waals’ forces between the layers are easy to overcome.
Question. Explain the nature of the covalent bond using the bond formation in CH3Cl.
Answer: The molecule of chloromethane (CH3Cl) consists of three elements i.e., carbon (Z = 6), hydrogen (Z = 1) and chlorine (Z = 17). Carbon atom has four valence electrons (2, 4) ; hydrogen has one (1) while chlorine has seven electrons in the valence shell (2, 8, 7). In order to complete its octet, carbon shares three valence electrons with three hydrogen atoms while one is shared with the electron of chlorine atom. The structure of covalent molecule may be written as follows :
Question. What is homologous series of compounds?
List any two characteristics of homologous series.
Answer: A series of compounds having similar structures and similar chemical properties in which the successive member differs in their molecular formula by –CH2 group is called homologous series.
(a) All the members of homologous series have similar chemical properties.
(b) Any two consecutive members differ in their molecular formula by a –CH2 group.
Question. Two non-metals A and B combine with each other by sharing of electrons to form compound C.
(a) What is the naturstronge of compound C ?
(b) Will it dissolve in water or organic solvents?
(c) Will it be a good or bad conductor of electricity?
(d) Will it have high or low melting/boiling point ?
Answer: (a) Covalent
(b) Usually soluble in organic solvents
(c) Bad conductor
(d) Usually low melting / boiling point.
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