Solutions of Metals and Non-metals (Page No - 168) - Chemistry Lakhmir Singh, Class 10 | Extra Documents, Videos & Tests for Class 10 PDF Download

Question 20:
Fill in the blanks in the following sentences :
(i) Two atoms of the same element combine to form a molecule. The bond between them is known as…………………………………bond.
(ii) Two chlorine atoms combine to form a molecule. The bond between them is known as
(iii) In forming oxygen molecule,………….. electrons are shared by each atom of oxygen.
(iv) In forming N2 molecule,……….. electrons are shared by each atom of nitrogen.
(v) The number of single covalent bonds in C2H2 molecule are…………………………
(vi) Melting points and boiling points of ionic compounds are generally………………… than those of covalent compounds.
Solution :
(i) Covalent
(ii) Covalent
(iii) Two
(iv) Three
(v) Two
(vi) Higher

Question 21:
(a) What is a covalent bond ? What type of bond exists in (i) CCl4, and (ii) CaCl2 ?
(b) What is an ionic bond ? What type of bond is present in oxygen molecule ?
Solution :
(a) The chemical bond formed by the sharing of electrons between two atoms is known as a covalent bond.
(i) Covalent bonds (ii) Ionic bonds
(b) The chemical bond formed by the transfer of electrons from one atom to another is known as an ionic bond.
Covalent bond is present in an oxygen molecule.

Question 22:
(a) What is an ion ? Explain with examples.
(b) What is the nature of charge on (i) a cation, and (ii) an anion ?
(c) Name the cation and anion present in MgCl₂. Also write their symbols.
Solution :
(a) An ion is an electrically charged atom (or group of atoms). Example: Sodium ion, Na + , magnesium ion, Mg ₂⁺ .
(b) (i) Positive charge (ii) Negative charge
(c) Cation: Magnesium ion, Mg ₂⁺
Anion: Chloride ions, 2Cl ^–

Question 23:
(a) What type of chemical bond is present in chlorine molecule ? Explain your answer.
(b) Explain the formation of a chlorine molecule on the basis of electronic theory of valency.
Solution :
(a) Covalent bond ; Because whenever two atoms of the same element combine to form a molecule, a covalent bond is formed.
(b) The atomic number of chlorine is 17, so its electronic configuration is 2,8,7. Chlorine atom has 7 electrons in its outermost shell and needs 1 more electron to complete its octet and become stable.
It gets this electron by sharing with another chlorine atom. So, two chlorine atoms share one electron each to form a chlorine molecule. Because the two chlorine atoms share electrons, there is a strong force of attraction between them which holds them together. This force is called covalent bond.
Now, each chlorine atom in the chlorine molecule has the electronic configuration 2,8,8 resembling its nearest inert gas argon. Since the chlorine atoms in a chlorine molecule have inert gas electron arrangements, therefore, a chlorine molecule is more stable than two separate chlorine atoms.

Question 24:
(a) Giving one example each, state what are (i) ionic compounds, and (ii) covalent compounds.
(b) Compare the properties of ionic compounds and covalent compounds.
Solution :
(a) (i) The compounds containing ionic bonds are known as ionic compounds. They are formed by the transfer of electrons from one atom to another.
Example: Sodium chloride, NaCl.
(ii) The compounds containing covalent bonds are known as covalent compounds. They are formed by the sharing of electrons between atoms. Example: Methane, CH ₄ .
(b) Ionic compounds
(i) Ionic compounds are usually crystalline solids.
(ii) Ionic compounds have high melting and boiling points.
(iii) Ionic compounds are usually soluble in water.
Covalent compounds
(i) Covalent compounds are usually liquids or gases.
(ii) Covalent compounds have low melting and boiling points.
(iii) Covalent compounds are usually insoluble in water.

Question 25:
Explain why :
(a) covalent compounds have generally low melting points.
(b) ionic compounds have generally high melting points.
Solution :
(a) Covalent compounds have generally low melting points because they are made up of electrically neutral molecules. So, the force of attraction between the molecules of a covalent compound is ve ry weak. Hence, only a small amount of heat energy is required to break these weak molecular forces.
(b) Ionic compounds are made of up of positive and negative ions. There is a strong force of attraction between the oppositely charged ions, so a lot of heat energy is required to break this force of attraction and melt or boil the ionic compound. Due to this, ionic compounds have high melting points.

Question 26:
(a) Give two general properties of ionic compounds and two those of covalent compounds.
(b) State one test by which sodium chloride can be distinguished from sugar.
Solution :
(a) Ionic compounds:
(i) They have high melting and boiling points.
(ii) They are usually soluble in water.
Covalent compounds:
(i) They have low melting and boiling points.
(ii) They are usually insoluble in water.
(b) An aqueous solution of sodium chloride conducts electricity but a sugar solution does not conduct electri city.

Question 27:
(a) Explain why, ionic compounds conduct electricity in solution whereas covalent compounds do not conduct electricity .
(b) Which of the following will conduct electricity and which not ?
MgCl₂, CCl₄, NaCl, CS₂, Na₂S Give reasons for your choice.
Solution :
(a) Ionic compounds conduct electricity in solution because they are made up of electrically charged ions but covalent compounds are made u p of electrically neutral molecules so they do not conduct electricity.
(b) Conduct electricity: MgCl₂ , NaCl, Na₂ S (Ionic compounds)
Do not con duct electricity: CCl₄ , CS₂ ( Covalent compounds) .

Question 28:
(a) Name one ionic compound containing chlorine and one covalent compound containing chlorine.
(b) How will you find out which of the water soluble compound A or B is ionic ?
Solution :
(a) Ionic compound: Sodium chloride, NaCl.
Cova lent compound: Carbon tetrachloride, CCl₄
(b) Out of A and B, the compound whose aqueous solution cond ucts electricity will be an ionic compound.

Question 29:
Explain why, a solution of cane sugar does not conduct electricity but a solution of common salt is a good conductor of electricity.
Solution :
Common salt is an ionic compound containing ionic bonds whereas cane sugar is a covalent compound containing covalent bonds. Since, ionic compounds conduct electricity and covalent compounds do not, hence common salt is a good conductor of electricity and cane sugar is a non-conductor of electricity.

Question 30:
Give the formulae of the compounds that would be formed by the combination of the following pairs of elements :
(a) Mg and N₂ (b) Li and O₂
(c) Al and Cl₂ (d) K and H
Solution :
(a) Mg₃ N₂
(b) Li₂ O
(c) AlCl₃
(d) KH

Question 31:
(a) What are noble gases ? What is the characteristic of the electronic configuration of noble gases ?
(b) What is the cause of chemical bonding (or chemical combination) of atoms of elements ?
Solution :
(a) There are some elements in group 18 of the periodic table which do not combine with other elements. These elements are helium, neon, argon, krypton, xenon and radon . They are known as noble gases or inert gases because they are unreactive.
If we look at the electronic configuration of noble gases, we would notice that except helium, all other inert gases have 8 electrons (helium has 2) in their outermost shells. This is considered to be the most stable arrangement of electrons.
(b) Atoms form chemical bonds to achieve stability by acquiring the inert gas electron configuration.

Question 32:
(i) Write electron-dot structures for magnesium and oxygen.
(ii) Show the formation of MgO by the transfer of electrons.
(iii) What are the ions present in this compound ?
Solution :

Question 33:
Draw the electron-dot structure of a hydrogen chloride molecule :
(i) Which inert gas does the H atom in HCl resemble in electron arrangement ?
(ii) Which inert gas does the Cl atom in HCl resemble in electron arrangement ?
Solution :

(i) Helium(ii) Argon

Question 34:
What type of bonding would you expect between the following pairs of elements ?
(i) Calcium and Oxygen
(ii) Carbon and Chlorine
(iii) Hydrogen and Chlorine
Solution :
(i) Ionic bonding.
(ii) Covalent bonding.
(iii) Covalent bonding.