Class 10 Chemical Bonding ICSE - What is a Chemical Bond?

ICSE Class 10 Questions on Chemical Bonding

What is a Chemical Bond?

1)   How do atoms attain noble gas configuration?

Ans. Atoms attain noble gas configuration by gaining, losing or sharing electrons.

W2)

Define:

(a)A chemical bond.

 A chemical bond may be defined as the force of attraction between any two    

  atoms, in a molecule to maintain stability.

(b) An electrovalent compound.

 The chemical compounds formed as a result of the transfer of electrons   

 between metallic and non metallic atoms is called electrovalent/ionic bond.

(c) A covalent compound.

The molecule formed due to sharing of electrons between two nonmetallic atoms called a covalent compound.

3)   What are the conditions for the formations of an electrovalent bond?

Ans.  i)Low Ionization potential

        ii) High electron affinity.

        iii) Large electronegativity difference.

4)   An atom has two electrons more than the noble gas configuration. What type of ion will it form?

Ans. Cation, as it will lose two electrons to obtain noble gas configuration.

5)   What type of compounds are usually formed between metals and non-metals and why? Mention the basic tendency of an atom which combines it with other atom.

Ans. Electrovalent compounds are formed between a metal and a non-metal as they form cations and anions respectively which results in the formation of electrovalent compounds. Also all the three conditions needed for the formation of an electrovalent bond are satisfied in this case. An atom tends to become stable and acquire an octet or duplet structure by losing, gaining or sharing of electrons.

6)   In the formation of the compound XY₂ an atom X given one electron to each Y atom. What is the nature of bonds in XY₂? Give two properties of XY₂.

Ans. Nature of bond: Electrovalent bond.

Properties of XY₂:

(i) It has high melting and boiling points.

(ii) It conducts electricity only in fused or aqueous state.

7)   An atom X has 2,8,7 electrons in its shells. It combines with Y having 1 electron in its valence shell.

 (i)What type of bond will be formed between X and Y?

(ii) Write the formula of the compound formed.

(iii) Would it be soluble in water?

Ans. (i)Electrovalent bond    (ii) YX   Y-metal, X- nonmetal

  (iii) It will be soluble in water.

8)The configuration of Chloride ion is the same as that of Argon atom. What is the difference between the two?

Ans. Chloride ion is negatively charged whereas argon atom is electrically neutral. Chlorine atom gains this electronic configuration by gaining one electron, while Argon atom has atomic number with electronic configuration

2,8,8.

9)Magnesium Chloride is an ionic compound while Hydrogen Chloride is a covalent compound. But both form ions in their aqueous solutions. Explain.

Ans. (i)As magnesium chloride is an ionic compound(formed by ions) it will  

           dissociate into ions when dissolved in water.

       (ii)Hydrogen Chloride is a polar covalent compound where Hydrogen is

           slightly positive and Chlorine is slightly negative due to small

           electronegative difference between H and Cl. Water being a polar

           solvent ionizes HCl. When Hydrogen Chloride is dissolved in it

          Hydrogen is attracted towards Oxygen and chlorine towards one of

           the   hydrogen’s present in water.

 That is why both Magnesium chloride and Hydrogen Chloride form ions in their aqueous solutions.

10)Compare:

(a) Sodium atom and sodium ion

(b) Chlorine atom and Chlorine ion.

With respect to:

          1). Atomic structure.     2). Electrical state.   3).chemical action  

Ans.  (a)  1. Sodium atom has 1 electron in its valence shell and has 3 shells

                whereas sodium ion   has 8 electrons in its outermost 2^nd shell.

                       2. Sodium atom is electrically neutral where as Sodium ion is

                          positively charged.

             3. Sodium ion is more stable than Sodium atom. Therefore Sodium

                 atom is more chemically active than Sodium ion

       (b)  1. Chlorine atom has 7 electrons in its valence shell whereas sodium

                  ion has 8 electrons in its valence shell.

             2. Chlorine atom is electrically neutral whereas chlorine ion is  

                  negatively charged.

             3. Chlorine atom is more chemically active than chlorine ion.

11) What are the conditions necessary for the formation of covalent

     molecules?

Ans.  Both atoms should have:

1. 4 or more electrons in their valence shell i.e. both are nonmetals.

2. High Electronegativity.

3. High electron affinity.

4. High ionization energy.

5. The electronegativity  difference between the combining atoms must be   

    either zero or negligible.

12) Elements A, B and C have atomic numbers 9, 20 ans 10 respectively.

(a) State which one is:

(i) A non- metal  -----  ‘A’      (ii) a metal   ------  ‘B’   

(iii) Chemically inert  ----  ‘C’

(b) Write down the formula of the compound formed by two of the above  

    elements.

Ans. BA₂

         13) Explain the following:

(a) Ionic compounds conduct electricity in fused or aqueous state.

     When ionic compounds are in solid state, there are no free ions as they   

     are held by strong electrostatic force of attraction. But when they are  

     dissolved in water or melted it has free ions. Hence it can conduct

     electricity in fused or aqueous state.

(b) Ionic compounds have high melting and boiling compounds while  

     covalent compounds have low melting and boiling points.

     In Ionic compounds, there is a strong force of attraction between the   

     oppositely charged particles. Therefore a large amount of energy is

     required to break the bond. That is why their melting and boiling points  

     are high. Whereas in  covalent compounds, the force of attraction

     between the particles is weak and the bond can be broken easily.

     Therefore their melting and boiling points are low.

(c)  Ionic compounds dissolve in water whereas covalent compounds do not.

     Ionic compounds are formed by ions and when they dissolved in  

     Water dissolve in it, as water is a polar covalent compound with high   

     dielectric constant ionizes these compounds. Only polar covalent compound dissolve in Water. e.g. NH₃, HCl.

         On the other hand covalent compounds are not formed by

     ions and do not dissociate into ions. So, they do not dissolve in water.

(d) Ionic compounds are usually hard crystals.

    These compounds have strong electro-static forces of attraction between

    their ions which cannot be separated easily. That is why ionic compounds

    are usually hard crystals.

14.) Five atoms are labeled from A to E.

Atoms                     Mass no.                        Atomic no.

    A                               40                                    20

    B                               19                                      9

    C                                 7                                      3

    D                               16                                      8

    E                               14                                      7

(a) Which one of these atoms:

(i)contains 7 protons: E           (ii) has E.C. 2,7: B

         (b) Write down the formula of the compound formed between

C and D. ----- C₂D

          (c) Predict which are:  (i) metals: A, C  (ii) non-metals: B, D, E

15) A solid is crystalline, has a high melting point and is water soluble. Describe the nature of the solid formed.

Ans. The solid formed is an ionic compound.

16) What is the difference between:

(a) ionic compounds and polar covalent compounds.

Ionic Compounds	Polar Covalent compounds
1.   Ionic compounds consist of a metal and non metal atoms only. 2.   Have large Electronegativity difference. 3.   Consist of ions / ions and molecules 4.   They have high melting points.	1.   Polar covalent compounds consist of nonmetal atoms only 2.    Have little difference in Electronegativity. 3.   They do not have any ions. 4.   They have low melting points.

(b) Ionic Compounds and Covalent compounds

Ionic Compounds	Covalent compounds
1.   They are the compounds formed between a metal and a non metal by transfer of electrons. 2.   They consist of ions. 3.   These compounds have high melting and boiling points due to strong electrostatic force of attraction. 4.   They conduct electricity only in fused or aqueous state.	1.   They are the compounds formed between two non metals by sharing of electrons. 2.   They do not consist of ions. 3.   These compounds have low boiling points due to weak Vander Waal’s forces. 4.   Non polar covalent compounds do not conduct electricity and polar covalent do in aqueous state.

(c) Polar covalent compounds and non-polar covalent compounds

Polar covalent compounds	non-polar covalent compounds
1. The particles constituting them have slightly negative and positive charges/slight charge distribution 2. They are soluble in other polar covalent compounds.e.g. H2O	1. No charge distribution. 2. Some of them are soluble in       polar solvents where as some      are not soluble.

17) The element ‘X’ has E.C. 2,8,18,8,1. Without identifying x,

(a) Predict charge and sign on a simple ion of ‘X’. ---- +1

(b) Write if ‘X’ will be an oxidizing agent or a reducing agent. ---- reducing agent( as it loses electron).

18) Match the atomic no. 4,14,8,15,19 with each of the following:

a) A solid non-metal of valency 3  ----   15.

b) A gas of valency 2 ----- 8

c) A metal of valency 1 -----19

          d) A non-metal of valency 4 ---- 14

               

          19) Elements X, Y & Z have atomic no. 6,9,12 respectively. Which one:

          a) Forms anion ---- Y

          b) Forms a cation ---- Z

          c) Has 4 electrons in its valence shell ---- X

        20) Taking NaCl as an ionic compound and CCl₄ as a covalent compound give

              four differences   between ionic and covalent compounds.

NaCl	CCl4
1. Formed when Sodium transfers one electron to Chlorine atom forming Na+ and Cl- 2. Large electronegative difference between Sodium and Chlorine. 3. Soluble in Water. 4. Conducts electricity in molten/ aqueous state due to presence of free ions.	1.   Formed by sharing of electrons forming four C-Cl bonds. No ions. 2.   Negligible Electronegativity difference between Carbon and Chlorine. It is non polar covalent compound. 3.   Soluble in Organic solvents. 4.   Does not conduct electricity as there are no free ions.

21) Name two compounds that are covalent when taken pure but produce

      ions when dissolved in water.

Ans.Hydrogen chloride- HCl, Ammonia-NH₃

22) An element M burns in O₂ to form an ionic bond MO. Write the formula of     

  the compounds formed if this element is made to combine with Chlorine

    and Sulphur separately.

Ans. MCl₂, MS ( as M is 2+ and S^2- and Cl^1-)

23) (a) What do you understand by redox reactions? Explain oxidation and

           reduction in terms of loss or gain of electrons.

Ans. A reaction in which oxidation and reduction occur simultaneously is

        known as redox reaction or oxidation-reduction reaction.

For example:

i) CuO   +    H₂                                            Cu   +H₂O  

      Here Hydrogen is the reducing agent. In the above reaction CuO is    

  reduced to Cu( loss of Oxygen) and also H₂ is oxidized to water (gain of Oxygen).

ii) Oxidation occurs when there is loss of electrons whereas reduction        

  occurs when there is gain of electrons.

          Cu²⁺ à Cu( reduction)

          H₂ à H⁺  ( Oxidation).

(b) Divide the following redox reactions into oxidation and reduction half

     reactions.

(i) Zn  +  Pb²⁺                         Zn²⁺   +   Pb

    Here Zinc loses electrons. So it is oxidation. Lead gains two electrons. So it is reduction.

(ii) Zn   +   Cu²⁺                           Zn²⁺   +   Cu

    Here zinc loses electrons  and it is oxidation. On the other hand copper    

gains electrons and it is reduction.

(iii) Cl₂   +   2Br^-                        Br₂ +   2Cl^—

      Here a) chlorine gains one electron so it is reduction. b) On the other

hand bromine loses one electron so it is oxidation.

24) Give the Electron dot structures of:

   (i)MgCl₂   (ii)   N₂   (iii) CH₄

Ans: a) (i)

                (i) MgCl₂

                (ii) N₂

     

               (iii) CH₄

                                 

                                

25) Predict the type of bonding in the following molecules

a) O₂  b)CaO  c)H₂O d)CH₄  e)NH₄⁺

Ans:

a)Covalent bond

b)Ionic bond/Electro valent

c)polar Covalent bond

d)Non polar Covalent bond

e)Covalent bond and coordinate bond

26) What do you understand by a dipole?Give one example.

Ans:

         A molecule that has both, slight positive and slight negative charge (polar

         covalent  molecule) is called a dipole molecule.

For example:

                        HCl                            H^∂+Cl^∂-

 This is because of slight electronegative difference between Hydrogen and Chlorine.Chlorine is slightly more electronegative than Hydrogen. Similar case in Water.

27) Define a coordinate bond and give conditions for its formation.

Ans: The bond formed between 2 atoms by sharing a pair of electrons, provided entirely by 1of the combining atoms, is called a coordinate bond or a dative bond.

Or type of covalency involves one of the combining atoms contributing both the shared electrons.

Conditions for the formation of coordinate bond:

1)One of the two atoms must have atleast one lone pair of electrons

2)Another atom should be short of at least a lone pair of electrons.

28)What do  you understand by lone pair & shared pair?

Ans: Lone pair of electons is the pair of electrons that hasn’t been shared with any     

    other atom during bonding whereas shared pair of electrons  are electrons which

    have been shared between two atoms.

29) Complete the following:

(a) When the nuclei of two different reacting atoms are of unequal mass, then a bond so formed is called polar covalent bond.

(b) In case of non-polar covalent bond, the covalent bond is formed in the middle of atoms and shared electrons are equally distributed.

(c) The ions in electrovalent compounds are held very strongly due to strong electrostatic forces.

30) What do you understand by polar covalent compounds? Explain by taking example of HCl.

Ans: In a molecule of HCl, the shared pair of electrons are pulled more towards chlorine due to the little differences in electronegativities and chlorine will get a slight negative charge and the hydrogen atom will get a slightly positive charge.

31) What is the essential difference in the nature of bonds when two combining atoms :

(a) differ in electronegativities and     (b) do not differ in electronegativities?

Ans: (a) If the two combining atoms differ in electronegativitives there are two

            cases possible:

(i)          It could be an electrovalent bond if the electronegativity difference is large. e.g. NaCl, PbBr₂

(ii)         It could be a covalent bond(polar covalent compound) if the electronegativity difference is less.    (HCl, NH₃)

(b) If there is no difference in electronegativities, it will form a non polar covalent bond.( Cl₂, O₂, N₂, CH₄)

                  

32)What is non-polar molecule ? Explain that methane molecule is non-polar.

Ans: A covalent bond between two similar atoms or dissimilar atoms which have little or zero electronegativity difference is called a non-polar covalent bond and those molecules thus formed are called non-polar compounds. The shared pair of electrons is equally distributed, no charge separation.

   e.g.In methane molecule, the electronegativity difference is little or zero. So it is a non-polar compound.

33) Give the structures of :

(i) Hydronium ion: H₃O⁺

 (ii) Ammonium ion:                                                   

                                                           

                           

                      

(iii)Hydroxyl ion:

                                            

                                             

                                 

34) Element M forms a chloride with the formula MCl₂ which is a solid with high melting point. M would most likely be in the same group as

(a)Na   (b)Mg   (c)Al     (d)Si

Ans: Element M will be in the group in which Mg is present(2^nd group).