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CAUSE AND MODES OF CHEMICAL COMBINATION
Atoms of different elements excepting noble gases donot have complete octet
so they combine with other atoms to form chemical bond. The force which holds the atoms or
ions together within the molecule is called a chemical bond and the process of their combina-
tion is called Chemical Bonding.
Chemical bonding depends on the valency of atoms. Valency was termed as
the number of chemical bonds formed by an atom in a molecule or number of electrons present
in outermost shell i.e., valence electrons. Valence electrons actually involved in bond formation
are called bonding electrons. The remaining valence electrons still available for bond formation
are referred to as non-bonding electrons.
Chemical combination takes place due to following reasons.
(1) Chemical bonding takes place to acquire a state of minimum energy and maxi-
mum stability.
(2) By formation of chemical bond, atoms convert into molecule to acquire stable con-
figuration of the nearest noble gas.
Modes : Chemical bonding can occur in the following manner.
Transfer of electrons from one atom to another Ionic bond
Mutual sharing of electrons between the atoms Covalent bond
Mutual sharing of electrons provided entirely by Co-ordination bond
one of the atoms
Electrovalent bond :
When a bond is formed by complete transfer of electrons from one atom to an-
other so as to complete their outermost orbits by acquiring 8 electrons (i.e., octet) or 2
electrons (i.e., duplet) in case of hydrogen, helium etc. and hence acquire the stable near-
est noble gas configuration, the bond formed is called ionic bond, electrovalent bond
or polar bond. Compounds containing ionic bond are called ionic, electrovalent or
polar compounds.
Example :
Cl Na Cl Na Cl Na or
CHEMICAL BONDING
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Some other examples are: MgCl2, CaCl2, MgO, Na2S, CaH2, AlF3, NaH, KH, O K2 , KI,
RbCl, NaBr, CaH2 etc.
(1) Conditions for formation of electrovalent bond
(A) Factors favourable for cation formation :
i) Low ionisation potential : Atom having very low ionisation potential forms the cation
very easily. Potassium (IP=495.57 kJ/mole) forms the cation more readily than
sodium(IP=519.82 kJ/mole)
ii) Low charge on the ion : Formation of cation carrying less positive charge is easy.
( 3 2
Al Mg Na
)
iii) Large atomic size : Atoms with large atomic size form cations easily
Cs Rb K Na Li
iv) Formation of cation with Inertgas configuration: Formation of cation having inert
gas configuration is very easy.
Example : Of the two cations Zn+2(2, 8, 18) and Ca+2(2, 8, 8), Ca+2 is more readily
formed and it is more stable than Zn+2and gives compounds with more ionic character.
(B) Factors favorable for anion formation :
i) High Electronegativity and Electron affinity : Atom having very high electron affinity
(or) electro negativity forms anion very easily. F > O > N
ii) Small atomic size : Small non metal atom forms anion very easily.
F Cl Br I
iii) Low charge on the ion : Formation of anion carrying less negative charge is easy.
2 3
F O N
iv) Formation of anion having inert gas configuration is very easy
Element
A
Element
B
Changes occuring
in the valence
electrons
Nature of the
bond formed
Low High Transfer of Ionic bond
High High Sharing of Covalent bond
Low Low Sea of molecular Metallic bond
orbital bond
e
e
e
Among NaCl, KCl, RbCl and CsCl , CsCl is readily formed.
Among NaF, NaCl and NaBr, NaF is readily formed.
Among NaF, CsF, MgO and CaO, CsF is readily formed.
No Bond is 100% ionic in nature. It has some percentage of covalent character
which is explained on the basis of Fajan’s rule.
v) Polarising Power: The ability of cation to polarise the near by anion is called polarising
power or polarsing ability.
vi) Polarisability: The tendency of anion to get distorted or polarised by the cation is called
its polarisability
vii) Polarising relates to cation:
Polarising power charge on cation
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1
size
viii) Polarisability relates to anion
Polarisability charge
size
ix) Polarising power increases covalent character increases
Example: Incase of 2 3 , , NaCl MgCl AlCl the polarisation increases, 2 3
Na Mg Al
Incase of AlF3, AlCl3, AlBr3, AlI3, the polarisability of halide ions increases as
F Cl Br I
x) Covalent character increases with increase in size of halide ion
xi) Cation with 18electrons in outer most shell bring greater polarisation of the anion than
those with inert gas configuration.
Example : CuCl is more covalent when compared to NaCl
Points to Remember
On moving down a group the polarising power of cation decreases
In periods polarising power increases from left to right
Polarisability of anion decreases from left to right
Polarisability of anion increases from top to bottom
Increase of polarisation brings more covalent character in an ionic com
pound
Increase in covalent character is indicated by the decrease in melting point
of the ionic compound
Polarisation increases covalent character increases melting point decreases
Lattice Enthalpy
The amount of energy released when the required number of oppositely
charged gaseous ions present at infinite distances come close and form one mole
of ionic crystalline solid is known as the lattice energy of the compound.
Lattice energy is directly proportional to the product of Z+ and Z– and inversely
proportional to the sum of the radii of cation and anion.
Lattice energy c a
Z Z
r r
where Z is charge on cation and Z is charge on
anion.
Determination of lattice energy (Born Haber cycle)
When a chemical bond is formed between two atoms (or ions), the potential en-
ergy of the system constituting the two atoms or ions decreases. If there is no fall in poten-
tial energy of the system, no bonding is possible, the energy changes involved in the
formation of ionic compounds from their constituent elements can be studied with the
help of a thermochemical cycle called Born Haber cycle.
Example : The formation of 1 mole of NaCl from sodium and chlorine involves
following steps :
Step I : Conversion of metallic sodium into gaseous sodium atoms
) ( ) (
1
g Na S s Na
mole
,
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where S= sublimation energy i.e., the energy required for the conversion of one
mole of metallic sodium into gaseous sodium atoms.
Step II : Dissociation of chlorine molecules into chlorine atoms
) ( 2 ) ( 2 g Cl D g Cl ,
where D = Dissociation energy of 2 Cl so the energy required for the
formation of one mole of gaseous chlorine atoms 2 / D .
Step III: Conversion of gaseous sodium atoms into sodium ions
e g Na IE g Na
mole
) ( ) (
1 ,
where IE = Ionisation energy of sodium.
Step IV: Conversion of gaseous chlorine atoms into chloride ions
EA g Cl e g Cl
mole
) ( ) (
1 ,
where EA = Electron affinity of chlorine.
Step V : Combination of gaseous sodium and chloride ions to form solid sodium
chloride crystal.
U s NaCl g Cl g Na mole
1
) ( ) ( ) ( ,
where U lattice energy of NaCl
The overall change may be represented as :
f H s NaCl g Cl s Na ), ( ) (
2
1
) ( 2 ,
where f H is the heat of formation for 1 mole of ) (s NaCl .
According to Hess’s law of constant heat summation, heat of formation of one mole of
NaCl should be same whether it takes place directly in one step or through a number of
steps. Thus,
U EA IE D S H f 2
1
2) Types of ions
The following types of ions are encountered :
(i) Ions with inert gas configuration : The atoms of the representative elements of
group I, II and III by complete loss of their valency electrons and the elements of group V,
VI, and VII by gaining 3,2 and 1 electrons respectively form ions either with 2
ns configura-
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tion or 6 2 p ns configuration.
(a) Ions with 2
1s (He) configuration : 2
, , Be Li H etc. The formation of
Li and 2
Be is diffi-
cult due to their small size and high ionisation potential.
(b) Ions with 6 2 p ns configuration : More than three electrons are hardly lost or gained in the
ion formation
Cations : 3 2 , , Al Ca Na etc.
Anions : , , , 3 2 N O Cl etc.
(ii) Ions with pseudo inert gas configuration : The 2
Zn ; ion is formed when zinc
atom loses its outer 4s electrons. The outer shell configuration of 2
Zn ions is
. 3 3 3 10 6 2 d p s The 10 6 2 nd np ns outer shell configuration is often called pseudo noble gas con-
figuration which is considered as stable one.
Examples: 3 2 2 2 , , , , , Ga Au Ag Cu Hg Cd Zn etc
(iii) Exceptional configurations : Many d- and f block elements produce ions with
configurations different than the above two. Ions like , , 2 3 Mn Fe etc., attain a stable con-
figuration half filled d- orbitals
5 6 2 2 5 6 2 3 3 3 3 ; 3 3 3 d p s Mn d p s Fe
Examples of other configurations are many.
) 3 3 3 ( ; ) 3 3 3 ( 3 6 2 2 2 6 2 2 d p s V d p s Ti
) 3 3 3 ( ; ) 3 3 3 ( 6 6 2 2 4 6 2 2 d p s Fe d p s Cr
However, such ions are comparatively less stable
(iv) Ions with 2
ns configuration : Heavier members of groups III, IV and V lose p-
electrons only to form ions with 2
ns configuration. 3 2 2 , , , Bi Pb Sn Tl are the examples of
this type. These are stable ions.
(v) Polyatomic ions : The ions which are composed of more than one atom are
called polyatomic ions. These ions move as such in chemical reactions. Some common
polyatomic ions are
4 NH (Ammonium);
3 NO (Nitrate)
3
4 PO (phosphate); 2
4 SO (Sulphate)
2
3 CO (Carbonate) ; 2
3 SO (Sulphite), etc.
(vi) Polyhalide ions : Halogens or interhalogens combine with halide ions to form
polyhalide ions.
2 4 3 , , ICl ICl I etc. Fluorine due to highest electronegativity and absence
of d-oribitals does not form polyhalide ions.
The atoms within the polyatomic ions are held to each other by covalent
bonds.
The electro valencies of an ion (any type) is equal to the number of charges
present on it.
(3) Method of writing formula of an ionic compound
In order to write the formula of an ionic compound which is made up of two ions (simple or
polyatomic) having electrovalencies x and y respectively, the following points are followed
:
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(i) Write the symbols of the ions side by side in such a way that positive ion is at the left
and negative ion at the right as AB.
(ii) Write their electrovalencies in figures on the top of each symbol as y x B A
(iii) Divide their valencies by H.C.F
(iv) Now apply criss cross rule as x y
A B
, i.e., formula x y B A
Examples :
Name of compound Exchange of valencies Formula Calcium
chloride CaCl2
Aluminium oxide Al2O3
Potassium phosphate K3Po4
Magnesium nitride Mg3N2
4) Difference between atoms and ions
The following are the points of difference between atoms and ions.
Atoms Ions
Atom s are perfect ly n eutral in ions nature,
i.e., n um ber of protons equa l to number of
electrons. Na (p rotons 11, of electron s 1 1),
Cl (Protons – 17, electrons –17) electro ns.
Ions are c ha rged particles, cat a re
positively charged , i.e., number of pro tons
m ore t han the number electrons. Anions
are negatively charged, i.e ., number of
proto ns less than the num be r of Na+
(pro tons 11, electrons 10 ), Cl– (protons 17,
e lectrons 18)
.Except noble gases, atom s h ave less than
8 e lectrons in the outermos t o rbit Na 2,8,1;
Ca 2,8,8 ,2 Cl 2,8,7; S 2, 8, 6
Io ns have generally 8 ele ctrons in the
outerm ost orb it, i.e., ns2np6 configu rat io n.
Ca2+ 2,8,8 Na+ 2,8; Cl– 2,8,8
Che mical activity is due to lo ss or gain or
sha ring of electrons as to acquire charge
noble ga s configuration.
The chemical activity is du e to the on the
ion . Oppositely charged io ns are held
together by electrost atic forces
5) Characteristics of ionic compounds
(i) Physical state : Electrovalent compounds are generally crystalline is nature.
The constituent ions are arranged in a regular way in their lattice. These are hard due to
strong forces of attraction between oppositely charged ions which keep them in their
fixed positions.
(ii) Melting and boiling points : Ionic compounds possess high melting and boil-
ing points. This is because ions are tightly held together by strong electrostatic forces of
attraction and hence a huge amount of energy is required to break the crystal lattice. For
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example order of melting and boiling points in halides of sodium and oxides of IInd group
elements is as,
, NaI NaBr NaCl NaF BaO CaO MgO
(iii) Hard and brittle : Electrovalent compounds are hard in nature. The hardness is due
to strong forces of attraction between oppositely charged ion which keep them in their
alloted positions. The brittleness of the crystals is due to movement of a layer of a crystal
on the other layer by application of external force when like ions come infront of each
other. The forces of repulsion come into play. The breaking of crystal occurs on account of
these forces or repulsion.
(iv) Electrical conductivity : Electrovalent solids donot conduct electricity. This is be-
cause the ions remain intact occupying fixed positions in the crystal lattice. When ionic
compounds are melted or dissolved in a polar solvent, the ions become free to move.
They are attracted towards the respective electrode and act as current carriers. Thus,
electrovalent compounds in the molten state or in solution conduct electricity.
(v) Solubility : Electrovalent compounds are fairly soluble in polar solvents and insoluble
in non-polar solvents. The polar solvents have high values of dielectric constants. Water is
one of the best polar solvents as it has a high value of dielectric constant. The dielec-
tric constant of a solvent is defined as its capacity to weaken the force of attraction
between the electrical charges immersed in that solvent. In solvent like water, the
electrostate force of attraction between the ions decreases. As a result there ions get
separated and finally solvated.
The values of dielectric constants of some of the compounds are given as
Compound Water Methyl AIc Ethyl AIc. Acetone Ether
Dielectric 81 35 27 21 4.1
constant
Capacity to dissolve electrovalent compounds decreases
Lattice energy and solvation energy also explains the solubility of electrovalent compounds.
These compounds dissolve in such a solvent of which the value of solvation en-
ergy is higher than the lattice energy of the compound. The value of solvation energy
depends on the relative size of the ions. Smaller the ion more of solvation, hence higher
the solvation energy.
Note: Some ionic compounds Example : 4 2 4 4 , , , , , CrO Ag AgI AgBr AgCl PbSO BaSO etc.
are sparingly soluble in water because in all such cases higher values of lattice energy
predominates over solvation energy.
(vi) Space isomerism :The electrovalent bonds are non-rigid and non-directional. Thus
these compound do not show space isomerism e.g. geometrical or optical isomerism.
(vii) Ionic reactions : Electrovalent compounds furnish ions in solution. The chemical
reaction of these compounds are ionic reactions, which are fast. Ionic bonds are more
common in inorganic compounds.
3
)e Precipitat (
3 NO K Cl Ag NO Ag Cl K
(viii) Isomorphism : Electrovalent compounds show isomorphism. Compound having
same electronic structures are isomorphous to each other.
(ix) Electrovalency and Variable electrovalency : The capacity of an element to form
electro-valent or ionic bond is called its electro-valency or the number of electrons lost
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or gained by the atom to form ionic compound is known as its electro-valency.
Certain metallic element lose different number of electrons under different condi-
tions, thereby showing variable electrovalency. The following are the reasons:
(a) Unstability of core : The residue configuration left after the loss of valency elec-
trons is called kernel or core. In the case of the atoms of transition elements, ions formed
after the loss of valency electrons do not possess a stable core as the configuration of
outermost shell is not 6 2 np ns but 10 to 1 6 2 d np ns . The outer shell lose one or more electrons
giving rise to metal ions of higher valencies.
Example : stable) (not 4 , 3 3 3 0 6 6 2 2 s d p s Fe
(stable) 4 , 3 3 3 0 5 6 2 3 s d p s Fe
(b) Inert pair effect : Some of heavier representative elements of third, fourth and fifth
groups having configuration of outermost shell 2 2 1 2 , np ns np ns and 3 2 np ns show va-
lencies with a difference of 2, i.e., (1 : 3) (2 : 4) (3 : 5) respectively. In the case of lower
valencies, only the electrons present in p–subshell are lost and ns2 electrons remain in-
tact. The reluctance of s-electron pair to take part in bond formation is known as the inert
pair effect.
I. MCQ’s with single correct answer
1. The number of valency electrons and the valency with respect to hydrogen are equal for
A) Sulphur B)Silicon C) Phosphorus D) Chlorine
2. The element having highest valency with respect to oxygen is
A) Sodium B). Aluminium C) Chlorine D) Sulphur
3. Metal ‘M’ forms a peroxide of the type MO2. Valency of the metal with respect to oxygen
A) 0 B) 1 C) 2 D) 4
4. An element A is tetravalent and another element B is divalent. The formula of the
compound formed by the combination of these elements is
A) A2 B B) A B C) A B2 D) A2 B3
5. An atom A has 2K, 8L and 3M electrons. Another atom B has 2 K and 6 L electrons.
The formula of the compound formed between A and B is
A) A B B) A2 B3 C) A3B2 D) AB2
6. Two elements X and Y the have following electron configurations, X= 1s2,2s2 2p6, 3s2
3p6, 4s2 and Y= 1s2,2s2 2p6, 3s2 3p5. The formula of the compound formed by the
combination of X and Y is
A) X Y2 B) X5 Y2 C) X2 Y5 D)X Y5
7. Which of the following exhibits variable valency
A) Na B) H C)Al D) S
8. In a short period, as the atomic number increases, the valency of elements with respect
to oxygen
A) decreases B) remains constant
C) first increases and then decreases D) increases
9. Electrovalency of non-metal atom is not equal to, that of the metal atom in
A) Sodium bromide B) Magnesium oxide
TEACHING TASK
CHEMISTRY CHEMICAL BONDING
VIII - CLASS 77
C)Aluminium nitride D) Potassium sulphide
10. Cation is isoelectronic with anion in
A) Sodium chloride B) Potassium Bromide
C) Lithium fluoride D) Rubedium bromide
11. Which of the following has pseudo inert gas configuration
A) Na+ B) Cu+ C)K+ D) S--
12. The Atomic numbers of three elements A. B and C are a, a + 1, and a + 2. C is an
alkalimetal. In a compound of A and C, the nature
A) Coordinate B)Covalent C) Ionic D) Metallic
13. An atom with atomic number 20 is most likely to combine chemically with the atom whose
atomic number is
A) 11 B) 16 C)18 D)10
14. Duplet configuration is not found in
A) hydride ion B) hydrogen molecule C) Lithium cation D) Be3+
15. If stability were attained with 6 electrons rather than with 8 electrons. What would be the
formula of the stable fluoride ion
A) F3+ B) F+ C)F- D) F2
16. The maximum valency of an element with atomic number 7 is
A) 2 B)5 C)4 ` D)3
17. Valency of sulphur in sulphuric acid is
A)2 B)4 C) 6 D)8
18. With the decrease in thermal energy of Gas molecules attaction forces and repulson forces
A) both increases B) both decreases
C) increases, decreases, respectively
D) decreases, increases, respectively
19. The maximum valency of sulphur is
A) 4 B)6 C) 8 D)7
20. Valency of the metal atomwith respect to oxygen is maximum in
A) Mn2O7 B) OsO4 C)MnO2 D) CrO3
21. When NaCl is dissolved in water the sodium ion is
A) Oxidised B) Reduced C) Hydrolysed D)Hydrated
22. The electronegativities of two elements are 0.7 and 3.0. the bond formed between
them would be
A) Ionic B) Covalent C) Co-ordinate covalent D) Metallic
23. Which of the following is a favourable factor for cation formation?
A) Low ionisation potential B) High electron affinity
C) High electronegativity D) Small atomic size
24. The co-ordination number of the cation in the face centred cubic lattice is
A) 4 B)8 C)3 D)6
25. The number of oppositely charged nearest neighbours to a Caesium ion in Caesium
Chloride lattice are
A) 8 B)6 C) 4 D) 2
II. Multi correct answer type questions:
26. It was found that atoms having atomic numbers of 2, 10, 18, 36, 54, 86 are very stable and
do not show any chemical reactivity, these elements were found to be gases and are
called: A) Inert gases
CHEMISTRY CHEMICAL BONDING
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B) Diatomic gases
C) Monoatomic gases D) Noble gases
27. Which of the following element(s) do not form molecules?
A) Helium B)Oxygen C) Nitrogen D) Argon
28. Which of the following will try to achieve helium configuration?
A) Hydrogen B)Lithium C) Berylium D) None of these
29. The common or group valency is equal to:
A) No. of valence electrons till group number 4.
B) 8 - no. of valence electrons after group number 4.
C) Only no. of electrons present in the valence shell.
D) None of the above.
III. Assertion & Reasoning type:
A) Statement-I, Statement-II both are true and Statement-II is the correct explanation
of Statement-I.
B) Statement-I, Statement-II both are true but Statement-II is not the correct
explanation of Statement-I.
C)Statement-I is true, Statement-II is false.
D)Statement-I is false, Statement-II is true
30. Statement I : Elements which lose electrons are called electropositive elements.
Statement II: Elements which gain electrons are called electronegative elements.
31. Statement I : Ionic compounds tend to be non-volatile
Statement II : Inter ionic forces in ionic compounds are weak
32. Statement I: Among Ca2+ and Zn2+ ions, Ca2+ is more stable than Zn2+
Statement II: Both Ca2+ and Zn2+ ions are diamagnetic
IV. Matching type:
33. Column-I Column-II
a) Sodium 1)2, 8, 8
b) Duplet configuration 2)Stable (or) inactive
c) Xe 3)Makes an element inactive
d) Ar 4)Unstable (or) active
5) 2, 8,8,18,18
34. Column-I Column-II
A) Incomplete octet 1) Acetic acid
B) Expansion of octet 2) BCl3
C) Octahedral Geometry 3) IF7
D) Dimerisation 4) SF6
V. Comprehension type:
The Chemical bond formed due to electron transfer is called ionic bond or electro
valent bond. Ionic bond will be formed more easily between the elements with low ionization
potential and high electron affinity. Energy changes involved during the formation of ionic
compound can be calculated by Born – Haber cycle. Lattice enthalpy changes are directly
proportional to the stability of ionic compound.
35. Which of the following has electrovalent bond?
A) HCl B) AlF3 C) CH4 D) BeCl2
36. Which of the following is more ionic?
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A) KF B) NaF C) MgF2 D) CaF2
37. Most stable ionic compound among the following is
A) Li2O B) MgO C)Cs2O D) KI
38. Born- Haber cycle is based on
A) Faradays law B)Gay-Lumar’s law
C)Emetons law D) Hess’s law
I. Single Answer type questions:
1. The electrons generally involved in bonding
A) are those that lie closest to the nucleus
B) are those for which the ionization energies are small
C) belongs to inner shells D) are free electrons
2. Chemical bond formation takes place when
A) energy is absorbed
B)forces of attration overcome forces of repulsion
C) forces of repulsion overcome forces of attraction
D) forces of attraction are equal to forces of repulsion.
3. During bond formation potential energy of the system
A) Increases B)decreases
C) remains the same D)cannot be predicted
4. The maximum number of valence electrons possible for atoms in the second period of
the periodic table is
A) 2 B) 8 C)18 D) 32
5. Which of the following covalent molecule is an exception to octet rule?
A) BeCl2
B)CO2
C)H2
O D)CH4
6. The molecule that deviates from octet rule is
A)NaCl B)BeCl2 C)MgO D)NH3
7 Which of the following bond is non polar ?
A) C-H B)O-H C)N-H D)F-F
8. In Covalency
A)Transfer of electrons takes place
B) Sharing of electrons takes place
C)Sharing of electrons by one atom only
D)None of these take place.
9. Potassium forms a highly ionic compound when it combines with
A)Chlorine B)Fluorine C) Bromine D)Iodine
10. Most ionic compound among the following is
A) Sodium fluoride B) Sodium Chloride
C) Sodium bromide D)Sodium iodide
11. Which of the following is not an ionic compound
A)Sodium hydride B) Carborundum
LEARNER’S TASK
BEGINNERS ( Level - I )
CHEMISTRY CHEMICAL BONDING
VIII - CLASS 80
C)Potassium oxide D)Calcium carbide
12. Least ionic compound among the following is
A) NaCI B)KCI C) CsI D) LiI
13. Which of the following is not an ionic compound
A) BaC2 B)AI2O3 C)CaH2 D)AICI3
14. The most ionic compound among the following is
A) KCI B) NaCI C) CsI D) CsF
15. The co-ordination number of sodium in sodium chloride is
A) 6 B) 4 C) 8 D) 3
16. Stability of ionic compound is influenced by
A)Electronegativity B) Lattice energy
C) Sublimation energy D) Electron affinity
17. Which of the following is not a property of ionic compounds
A) They are solids
B) They have high melting points
C)They are conductors in molten state
D) They exhibit space isomerism
18. Which of the following conducts electricity
A)Crystalline NaCI B)Fused NaCI
C)Molten sulphur D)Diamond
19. Which of the following is not a correct statement about an ionic compound
A)The higher the temperature, the more the solubility
B) The higher the dielectric constant of the solvent, the more the solubility
C)The higher the dipole moment of the solvent, the more the solubility
D) The higher the lattice energy, the more the solubility
20. In a crystal cations and anions are held together by
A) Electrons B) Electrostatic forces
C) Nuclear forces D)Covalent bonds
21. Fused ionic compounds
A)are insulators B) are used as semi-conductors
C)conduct electricity D) do not conduct electricity
22. Compared with covalent compounds, electro-valent compounds, generally have
A)Low melting points and low boiling points
B) Low melting points and high boiling points
C) High melting points and low boiling points
D) High melting points and high boiling points
23. Most favourable conditions for electrovalency are
A) Low charge on ions, large cation and small anion
B) High charge on ions, small cation and large anion
C) High charge on ions, large cation and small anion
D) Low charge on ions, small cation and large anion
24. An electrovalent compound is made up of
A) Electrically charged particles B) Neutral molecules
C) Neutral atoms D)Electrically charged atom or group of atoms
25. Ionic reactions are
A)Fast B) Slow C) Very slow D) medium
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II. Multi correct answer type questions:
26. Atoms can lose or gain _________ number of electrons. A )
1 B) 2 C) 3 D) 4
27. Which of the following true for ionic compounds?
A) They are hard solids
B) They can be broken down into pieces very easily
C) They are soluble in non-polar solvents
D) None of the above
28. Which of the following are true? A )
Ionic compounds exists as solid.
B) Ionic compounds have high melting point and high boiling point.
C) Ionic compounds undergo chemical reactions quickly in aqueous solutions.
D) None of these.
29. Which of the following statements are correct about ionic bond formation?
A) Ionic bond is formed between an atom of low ionisation potential and an atom
of high electron affinity.
B) Ionic bond is formed by the transfer of one or more electrons from one atom to the
other.
C) Generally oxides, Halides and Sulphides of alkali and alkaline earth metals are
ionic
D) None of the above.
30. Among the following which is correct information about the formation of cation?
A) Formation of cation is exothermic. B) In this energy releases.
C) It is an endothermic process. D) It is an energy absorbing process
III. Assertion & Reasoning type
1. Statement-I, Statement-II both are true and Statement-II is the correct explanation of
Statement-I.
2. Statement-I, Statement-II both are true but Statement-II is not the correct
explanation of Statement-I.
3. Statement-I is true, Statement-II is false.
4. Statement-I is false, Statement-II is true
31. Statement I : KF is more ionic than NaCl.
Statement II: Compounds having large cation and small anion is more ionic than
compound having small cation and large anion.
32. Statement I : Graphite is a good electrical conductor.
Statement II : The free electrons in graphite conducts electricity.
33. Statement I : NaCl is bad conductor in the solid state
Statement II : Na+ and Cl– ions are not free in the solid state
34. Statement I : Ionic compounds exhibits isomerism
Statement II : Ionic bond is non directional bond
ACHIEVERS ( Level - II )
CHEMISTRY CHEMICAL BONDING
VIII - CLASS 82
IV. Matching type:
35. Column-I Column-II
a) Ionic compounds in aqeous 1) Good conductor of electricity
b) Ionic compounds in solid state 2) Bad conductor of electricity
c) ZnSO4. 7H2O and FeSO4. 7H2O 3) Isomorphs
d) Best polar solvent 4) Water
5) CHCl3
36. Column-I Column-II
a) C2H6 1) Ionic bond
b) Iron wire 2) Metallic bond
c) H2O 3) Coordinate, covalent bonds
d) H3O+ 4) Covalent bond
37. Column I Column II
a) Electron deficent 1) ClF3
b) odd electron molecule 2) BeCl2
c) Expansion of octet 3) BF3
d) T shaped molecule 4) NO
V. Comprehension type:
When anions and cations approach each other, the valence shell of anions are
pulled towards cation nucleus and thus, shape of anion is deformed, The phenomenon of
deformation of anion by a cation is known as polarization and the ability of the cation to
polarize the anion is called as polarizing power of cation. Due to polarization, sharing of
electrons occurs between two ions to some extent and the bond shows some covalant
character.
The magnitude of polarization depends upon a number of factors. These factors were
suggested by Fajan and are known as Fajan’s rules.
1) Greater is the polarization in a molecule, more is covalent character.
2) As the charge magnitude on cation increases, its tendency to polarize the
anion increases.
3) As the size of the cation decreases or size of the anion increases, the
polarization increases.
4) The cations with 18 electrons in the outermost shell bring greater polarization of
the anion than those with inert gas configuration even both the cations
have same size and same charge.
38. In which of the halides, there is maximum polarization?
A) AlF3 B) AlCl3 C) AlBr3 D) AlI3
39. Which is most covalent in nature?
A) NaCl B) MgCl2 C) AlCl3 D) CaCl2
40. Which has the minimum melting point?
A)CaF2 B) CaCl2 C) CaBr2 D) CaI2
CHEMISTRY CHEMICAL BONDING
VIII - CLASS 83
Discriptive type
1. Expain ionic bond with examples.
2. Explain the favourable conditions for the formation of ionic bond.
3. explain Fazans rule.
MCQ’s with single correct answer
1. Metal ‘M’ forms a peroxide of the type MO2. Valency of the metal with respect to oxy-
gen
A) 0 B) 1 C) 2 D) 4
2. Electrovalency of non-metal atom is not equal to that of the metal atom in
A) Sodium bromide B) Magnesium oxide
C) Aluminium nitride D) Potassium sulphide
3. Valence of sulphur in sulphuric acid is
A) 2 B) 4 C) 6 D) 8
4. Variable valence is a property of
A) Alkali metals B) Transition metals
C) Alkaline earth metals D) Inert gases
5. The molecule that deviates from octet rule is
A) NaCl B) BeCl2 C) MgO D) NH3
6. In a crystal cations and anions are held together by
A) Electrons B) Electrostatic forces
C) Nuclear forces D) Covalent bonds
7. Most favourable conditions for electrovalence are
A) Low charge on ions, large cation and small anion
B) High charge on ions, small cation and large anion
C) High charge on ions, large cation and small anion
D) Low charge on ions, small cation and large anion
8. Most ionic bond is present in
A) LiH B) HF C) CsH D) HI
9. The electronegativities of F,Cl,Br and I are 4.0,3.0,2.8,2.5 respectively. The hydrogen
halide with a high percentage of ionic character is
A) HF B) HCl C) HBr D) HI
10. Ionic reactions are
A) Fast B) Slow C) Very slow D) medium
11. Melting point is very high for
A) KCl B) KBr C) KI D) KF
12. Which of the following is not an ionic compound
A) BaC2 B) Al2O3 C) CaH2 D) AlCl3
LECTURE TASK.
I 1. B 2. C 3. B 4. C 5. B 6. A 7. D 8. C 9. D
EXPLORERS ( Level - III )
RESEARCHERS ( Level - IV )
CHEMISTRY CHEMICAL BONDING
VIII - CLASS 84
10. D 11. B 12. C 13. B 14. D 15. B 16. B 17. C 18. C
19. B 20. B 21. D 22. A 23. A 24. D 25. A
II 26.A,C,D 27.A,D 28.A,B,C 29.A,B
III 30. B 31. C 32. B
IV 33. a-4,b-2,c-5,d-1 34. a-2,b-3,4,c-4,d-1
V 35. B 36. A 37. C 38. D
STUDENT TASK.
LEVEL-I
I 1. B 2. B 3.B 4. B 5. A 6.B 7. D 8. C 9.B
10. A 11.B 12. D 13.B 14. D 15. A 16. B 17. D 18. B
19. C 20. B 21. C 22. D 23. A 24. D 25. A
LEVEL-II
II 26.A,B,C,D 27.A,C 28.A,B,C 29.A,B,C 30. C,D
III 31.A 32. A 33. A 34. D
IV 35. a-1,b-2,c-3,d-4 36. a-4,b-2,c-4,d-3 37. a-2,3,b-1,3,4,c-1,d-1
V 38. A 39.C 40.D
Level - IV 1. C 2. D 3.C 4. B 5. B 6.B 7. A 8. C 9.A
10. A 11.D 12. D