II. Answer briefly:
1. How do atoms attain Noble gas electronic configuration?
Answer: Atoms can combine either by transfer of valence electrons from one atom to another or by sharing of valence electrons in order to achieve the stable noble gas electronic configuration.
2. NaCl is insoluble in carbon tetrachloride but soluble in water. Give reason.
Answer: NaCl is an ionic compound, it is soluble in polar solvent (water). Whereas CCI4 is a covalent compound. So it is insoluble in polar solvent (water). But it is soluble in non-polar solvents.
3. Explain Octet rule with an example.
Answer: The tendency of atoms to have eight electrons in the valence shell is known as the ‘Octet rule’ or the ‘Rule of eight’
For example, Sodium with atomic number 11 will readily loose one electron to attain Neon’s stable electronic configuration. Similarly, chlorine has electronic configuration 2,8,7. To get the nearest noble gas (i.e. Argon) configuration, it needs one more electron. So chlorine readily gains one electron from other atom and obtains stable electronic configuration. Thus elements tend to have stable valence shell (eight electrons) either by losing or gaining electrons.
4. Write a note on different types on bonds.
Answer: There are different types of chemical bonding possible between atoms which make the molecules. Depending on the type of bond they show different characteristics or properties.
5. Correct the wrong statements.
(a) Ionic compounds dissolve in non polar solvents.
(b) Covalent compounds conduct electricity in molten or solution state.
(a) Covalent compounds dissolve in non-polar solvents, (or) Ionic compounds dissolve in polar solvents.
(b) Ionic compounds conducts electricity in molten or solution state.
6. Complete the table give below.
7. Draw the electron distribution diagram for the formation of Carbon di oxide (CO2) molecule.
8. Fill in the following table according to the type of bonds formed in the given molecule.
CaCl2, H2O, CaO, CO, KBr, HCl, CCl4, HF, CO2, AI2 Cl6
9. The property which is characteristics of an Ionic compound is that
(a) it often exists as gas at room temperature.
(b) it is hard and brittle.
(c) it undergoes molecular reactions
(d) it has low melting point.
Answer: (b) it is hard and brittle
10. Identify the following reactions as oxidation or reduction.
(a) Na → Na+ + e−
(b) Fe3+ + 2 e− → Fe+
11. Identify the compounds as Ionic/Covalent/Coordinate based on the given characteristics.
(a) Soluble in non polar solvents
(b) Undergoes faster/instantaneous reactions
(c) Non conductors of electricity
(d) Solids at room temperature
(a) Co-ordinate Covalent compound.
(b) Ionic compound.
(c) Covalent compound.
(d) Ionic compound.
12. An atom X with atomic number 20 combines with atom Y with atomic number 8. Draw the dot structure for the formation of the molecult XY.
13. Considering MgCl2 as ionic compound and CH4 as covalent compound give any two differences between these two compounds.
MgCI (Ionic compound)
1. It is formed by the transfer of electrons (2e −) from a metal magnesium (Mg) to a non - metal atom chlorine (CI)
2. In Mg Cl2, strong electrostatic force of attraction exist between magnesium cation (Mg2+) and chloride atoms (Cl−)
CH4 (covalent compound)
1. It is formed by sharing of electrons between the non-metal atoms carbon and hydrogen
2. In CH4, weak force of attraction exist between carbon atom and four hydrogen atoms.
14. Why are Noble gases inert in nature?
Answer: Noble gases have stable valence electronic configuration. So noble gas atoms neither have any tendency to gain nor lose electrons and their valency is zero. Thus they are said to be inert.
III. Answer in detail:
1. List down the differences between Ionic and Covalent compounds.
• Formed by the transfer of electrons from a metal to a non-metal atom.
• Strong electrostatic force of attraction between cations and anions.
• Solids at room temperature.
• Conducts electricity in molten state or in solutions.
• Have high melting and boiling points.
• Soluble in polar solvents.
• Hard and brittle.
• Undergo ionic reaction which are fast and instantaneous.
• Formed by sharing of electrons between non-metal atoms.
• Mutual sharing of electrons and so weak force of attraction between atoms.
• Gases, liquids and soft solids.
• Non-conductors of electricity.
• Have low melting and boiling points.
• Soluble in non-polar solvents
• Soft and waxy.
• Undergo molecular reactions which are slow.
2. Give an example for each of the following statements.
(a) A compound in which two Covalent bonds are formed.
(b) A compound in which one ionic bond is formed.
(c) A compound in which two Covalent and one Coordinate bonds are formed.
(d) A compound in which three covalent bonds are formed.
(e) A compound in which coordinate bond is formed.
(a) Oxygen molecule (O2) (O = O)
(b) Sodium Chloride (NaCl)
(c) Carbon monoxide (C O)
(d) Nitrogen molecule (N2) (N ≡ N)
(e) NH3 → BF3
3. Identify the incorrect statement and correct them.
(a) Like covalent compounds, coordinate compounds also contain charged particles (ions). So they are good conductors of electricity.
(b) Ionic bond is a weak bond when compared to Hydrogen bond.
(c) Ionic or electrovalent bonds are formed by mutual sharing of electrons between atoms.
(d) Loss of electrons is called Oxidation and gain of electron is called Reduction.
(e) The electrons which are not involved in bonding are called valence electrons.
(a) Incorrect statement. Like covalent compounds, co-ordinate compounds also do not contain charged particles (ions), so they are bad conductors of electricity.
(b) Incorrect statement. Ionic bond is a strong bond when compared to hydrogen bond.
(c) Incorrect statement. Covalent bonds are formed by mutual sharing of electrons between atoms. (or) Ionic or electrovalent bonds are formed by transfer of electrons between atoms.
(d) Correct statement
(e) Incorrect statement. The electrons which are not involved in bonding are called lone pair of electrons.
4. Discuss in brief about the properties of coordinate covalent compounds.
Answer: The compounds containing coordinate covalent bonds are called coordinate compounds.
(a) Physical state - These compounds exist as gases, liquids or solids.
(b) Electrical conductivity - Like covalent compounds, co-ordinate compounds also do not contain charged particles (ions), so they are bad conductors of electricity.
(c) Melting point - These compounds have melting and boiling points higher than those of purely covalent compounds but lower than those of purely ionic compounds.
(d) Solubility - Insoluble in polar solvents like water but are soluble in non-polar solvents like benzene, CC14, and toluene.
(e) Reactions - Co-ordinate covalent compounds undergo molecular reactions which are slow.
5. Find the oxidation number of the elements in the following compounds.
(a) C in CO2
(b) Mn in MnSO4
(c) N in HNO3
(a) C in CO2
1(C) + 2(0) = 0
lx + 2(-2) = 0
x - 4 =0
x = +4
ON of C in CO2 is +4
(b) Mn in MnSO4
1 (Mn)+ 1(S) + 4(0) = 0
x+1 (+6) + 4(-2) = 0
x + 6 - 8 = 0
x - 2 =0
x = +2
ON of Mn in MnSO4 is +2
(c) N in HNO3
1(H) + 1 (N) + 3(0) = 0
1 (+1)+ 1 (x) + 3(-2) = 0
+ 1 + x - 6 = 0
x - 5 = 0
ON of N in HNO3 is+ 5.