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Chemistry Chapter 6 Class First Year (11th) Chemical Bonding

Chemical Bonding

Q.No.1: What is the chemical bond?

Ans: the force of attraction that holds two or more atoms in form of molecules and compound is called chemical bond.

Example:  

  • Two atoms of hydrogen are joined by chemical bond in form of molecule.
  • Na and Cl ions are joined together with help of chemical bond.
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Q.No.2: Why atom forms chemical bond?

Ans: Everything in this universe tries to become stable. Atoms will be stable if they have 2 or 8 electrons in their valence shell. For this purpose, atoms lose, gains and share electrons. By doing this chemical bond is formed.

Q.No.3: Define octet rule and duplet rule.

Ans:

Octet RuleDuplet rule
The tendency of atoms to have eight electrons in their valence shell is called octet rule Example: Na loses one electron to have 8 electrons in its valence shell.Chlorine accepts one electron in its valence shell.The tendency of atoms to attain two atoms in their valence shell is called Duplet rule. Example Hydrogen atom tends to attains 2 electrons in its valence shell by mean of gaining, losing or sharing of electrons.

Q.No.4: Octet rule is not a universal comment?

Ans: the are many example of formation of compounds in which octet rule is not obeyed.

  • Some elements during formation of compounds have less electrons than 8 e.g. ,
  • Some elements during formation of compound has excess electrons e.g.

So octet rule is not universal.

Q.No.5: What is bond distance?

Ans: the distance at which attractive forces dominate repulsive forces and atoms combine to form a stable molecules, which is called bond distance.

Example: for  molecule its value is 75.4 pm.

Q.No.6: what is an atomic radius? Give its trend in periodic table?

Ans: the average distance between nucleus of an atom and its outermost shell is called atomic radii

OR

The one half distance between nuclei of two alike atoms is called atomic radii.

Example:       

  • The atomic radius of carbon is 77pm
  • The atomic radius of helium is 152 pm

Trends in periodic table in group

Atomic radii increase from top to bottom in group due to following reasons

  • Extra—shells are added
  • Shielding effect increase
  • Nuclear charge decrease.

In Periods

Atomic radius decrease as we move from left to right in periodic table due to following reasons.

  • No shells remains same
  • Shielding effect decreases.
  • Nuclear charge decreases.

Q.No.7: radius of an atom cannot be determined exactly. Why?

Ans: we cannot measure size of atom exactly due to following reasons.

  • Atoms have no sharp boundary as probability of finding electrons can never becomes zero.
  • The nearly atoms can also effect from the probability of distribution of electrons.

Q.No.8: Why size of cation is always smaller than its parent itom?

Ans: the size of cation is always smaller than its parent atom due to following reasons.

  • Cation is formed by loss of electron.
  • As atom lose electron, nuclear charge increase.
  • Due to increase in nuclear charge, electronic cloud decreases.

Due to increase nuclear charge, nucleus exert more nuclear charge and size becomes smaller.

Example:  the size of Na atom is 154 pm while size of  is 95pm.

Q.No.9: Why size of anion is greater than its parent’s atom?

Ans: the radius of anion is greater than its parent atom due to following reasons.

  • Anion is formed due to gain of electrons
  • As atom gain electrons, nucleus charge decrease.
  • Due to decrease in nuclear charge, atomic radii increase.

Example:

The size of Cl is 99 pm  and its anion  is 181 pm.

Q.No.10: what is ionization energy? Discuss its trends in periodic table?

Ans: the minimum amount of energy required to remove electrons from valence shell of an atom is gaseous state , is called ionization potential.

Trends in periodic table:

In Groups

Ionization energy decreases from top to bottom in group due to following reasons

  • From top to bottom , new shells are added.
  • Shielding effect increase.
  • Atomic radii increases.
  • Due to increase in atomic radius, nuclear charge decreases.
  • As nuclear charge decreases, it becomes easier to remove electron ionization energy decreases.

Periods:

Ionization energy increases as we move from left to right in periods due to following reasons

  • No. of shells remain same
  • Shielding effect does not increase significantly.
  • Atomic radii decreases.
  • Due to decreases in atomic radius, nuclear charge increases.
  • Due to increases in nuclear charge it becomes difficult for an atom lose electrons, hence ionization energy decreases.

Q.No.11: Why 2nd Ionization energy is greater than first one?

Ans: the second ionization energy is greater than first one due to following reasons

  • When one electron is removed nuclear charge increases.
  • When nuclear charge increases atomic radius decreases.

So, nucleus entrapped outer most electrons more strongly, that’s why to remove second electron more energy is required.

Q.No.12: Ionization energy is an index to metallic character {Electro Positivity character}. Justify?

Ans: The ionization energy is an index to metallic character in the following ways.

  • The element with low ionization energy is metals.
  • The element with high ionization energy is non-metals.
  • The element with intermediate ionization energy is metalloids.

Q.No.13: Write down factor affecting ionization energy?

Ans: following factors effecting ionization energy

  • Atomic radius
  • Nuclear charge.
  • Shielding effect.
  • Nature of sub-shell.

Q.no.14: How Ionization energy tell us about valency?

Ans: we can guess valency of element from gap between first ,. Second, third and high ionization energy in following ways

  • If there is big gap between first and second ionization energy then valency is 1.
  • Similarly, if gap between second and third ionization energy is big then valency is 2.

Q.No.15: Define electron affinity. Discuss its trends in periodic table?

Ans: the amount of energy released, when an electron is added in valence shell of an atom is called electron affinity.

Trends in periodic table:

In Periods:

E.A. increases from left to right in periods due to following reasons.

(i)           when we move from left to right no. of shells remain same.

(ii)           Atomic radius decreases.

  • Nuclear charge increases.
  • Due to increase in nuclear charge, E.A. Increases.

In Groups:

E.A decreases from top to bottom in group due to following reasons.

(i)    New shells are added.

(ii)   atomic radius increases.

  • Nuclear charge decreases
  • Due to decrease in nuclear charge, E.A decrease.

Q.No.16:Why E.A of fluorine is less than chlorine?

Ans: E.A decreases from top to bottom in group usually. But in case of halogens E.A of fluorine (which is above than chlorine) is less than chlorine. The reason is that seven electrons of fluorine are present in 2s and 2p sub-shells. These sub-shells have thick electronic cloud. This thick electronic cloud repels coming electrons. That’s why E.A of fluorine is less than chlorine. E.A of fluorine is -329 KJ/mol while of chlorine is -341 KJ/mol.

Q.No.17:Why second electron affinity is always positive?

OR

Why formation of di-negative Ion is endothermic process?

Ans: Second electron affinity is always positive due to following reasons.

  • When we add second electron in uni-negative ion. Incoming electron repelled by already present electrons.
  • To overcome this repulsion energy is provided.
  • Hence energy is provided so second electron affinity is positive or formation of di-negative ion is endothermic process.’

Q.No.18:Define Electro negativity. discuss its trends.

Ans: the ability of an atom to attract shared pair of electrons towards itself is called electro negativity.

Example:

  • E.N of fluorine is 4.00
  • E.N of Cesium is 0.7

Trends in periodic table

In Groups

E.N decreases from top to bottom in groups due to following reasons.

(i)               as we move from top to bottom , new shells are added.

(ii)             shielding effect increases.

  • Atomic radius increases.
  • Nuclear charge decreases.
  • Due to decrease in nuclear charge, the tendency to attract electrons decreases.

In Periods:

E.N decreases from left to right in periods due to following reasons.

(i)               No. of shells remains constant.

(ii)  shielding effect decreases.

  • Nuclear charge increases.
  • Atomic radius decreases.
  • Due to increases in nuclear charge, the tendency to attract electrons increases.

Q.No.19:write down application of electro negativity?

Ans: the nature of bond can be determined by E.N  difference in following ways.

  • If E.N difference between two atoms is zero, then bond will be non-polar.
  • If E.N difference between two atoms is greater than 1.7 bond will be ionic.
  • If E.N difference between two atom in equal to 1.7 , then bond will be ionic and covalent.

Q.No.20: No bond in chemistry is 100% ionic. Comment?

Ans: E.N difference helps us to predict nature of covalent bond. If it is greater than 1.7. the chance of bond to be ionic are greater but no 100%. That’s why no bond in chemistry is 100 % ionic bond. The CsF has maximum ionic character and that is 92%.

Q.No.21:Difference between polar and non-polar bond?

Ans:

Sr. No.Non Polar covalent bondPolar covalent bond
IThe covalent bond present between similar atoms is called non-polar covalent bond.The covalent bond present between different atoms is called polar covalent bond
IIThe bond between Cl-Cl, and H-H is an example of non-polar covalent bondThe bond between H-O , and H-F is an example of polar covalent bond.

Q.No.22: why sigma bond is more diffuse than pi bond?

Ans: sigma bond is formed by head to head overlap of two partially filled orbitls. Here electron density is symmetrically spread around bond axis. The pi bond is formed by parallel overlap of two partially filled orbital. Here the electron density is spread over and below bond axis. It is the reason that sigma bond is more diffused than pi-bond.

Q.No.23:  and  can form coordinate covalent bond with  but  can not do so, why?

Ans:  and  both have ionic pairs of electrons. These ionic pairs are available for donation. So they can donate these ionic pairs to  In case of  there is no pair of electron.

That’s why  and  can form coordinate covalent bond with  but   cannot.

Q.No.24:Write down limitation of Lewis model.

Ans: Lewis Model explains only formation of bond by transfer and sharing of electrons. It has following limitation.

  • It can not explain angle.
  • It can not explain bond length and bond energy.
  • It can not explain paramagnetic behavior of elements.
  • It can not explain shape of compound or molecules.

Q.No.25: Who give VSEPR Theory? Write postulate of this theory.

Ans: this theory was put forward ny Nyholm, and Gillespie.

Postulate:

  • Both bond pair and lone pair of electrons determine geometry of molecule.
  • Electron pairs around the central atom remain at a maximum distance to word repulsion.
  • The lone pair of electrons occupy more space than bond pair.
  • The repulsion between electrons pair decrease in following order. Lone pair- bond pair> lone pair – bond pair > bond pair – bond pair. These repulsions are called vander wall’s repulsion or exchanmge repulsion.
  • A multiple bond ( double and triple bond) occupies more space than single bond. However it is counted as single bond.

Q.No.26: Differentiate between lone and electron pair?

Ans:

Sr.No.Lone pairBond pair
iThe electron pair which do not take part in bond formation is called lone pairThe electron pair which takes part in bond formation is called bond pair.
ii electron pair at nitrogen Nitrogen atim is lone pair.  H    |  :N— H    |   H   Three electrons by nitrogen is used for formation of bond with hydrogen.

Q.No.27: why lone pair of atom occupy more space than bond pair?

Ans: lone pair is under influence of one nucleus while bond pair is attracted by nucleus. Due to less nuclear attraction to lone pair its electronic charge is spread to more in space than that of bond pair.

Q.No.28 Bond angles of  is  which is less than in  . Justify?

Ans: Fluorine is more electronegative atom than hydrogen. In  due to high electro negativity of fluorine , fluorine attracts lone pair towards itself. Due to this attraction bond angle between  reduced. That’s why bond angle of () is less than  

Q.No.29:  Give postulates of valence bond theory?

Ans:  In 1930 Linus Pauling and J.C. Salter put forward this theory , it was wave mechanics based about covalent bond.

Postulates:

  • Covalent bond is formed by overlapping of the partially filled atomic orbitals.
  • As result of overlap, the electrons with opposite spin becomes paired to stabilized themselves.
  • Larger the overlap, stronger is the bond.
  • The direction of covalent bond is determined by the direction of overlapping orbital’s.

Q.No.30:The Bond angle of  and  are not   like that of  although O and N atoms are  hybridized. Justify?

Ans: In  and  there is  hybridization like . The angle between  orbital’s should be of . But we know that  has one lone pair and : has two lone pairs. There is repulsion due to presence of lone pair. That’s why bond angle of  () and () is less than  ().

Q.No.31:Why M.O.T is superior than V.B.T?

Ans: No, doubt V.B.T plays vital role to understand chemical bonding. But V.B.T is unable to describe paramagnetic behavior of elements like .But M.O.T. is able to explain both chemical bonding and paramagnetic behavior, that’s why M.O.T is superior to V.B.T.

Q.No.32: What do you mean by paramagnetic and diamagnetic behavior?

Ans:the substance which is attracted by magnet due to presence of unpaired electrons is called paramagnetic substance and this phenomenon is called paramagnetic behavior. Greater will be number of unpaired electrons , stronger will be attraction.

The substance which is not attracted by magnet is called Diamagnetic Substance and this phenomenon is called Diamagnetic Behavior.

Q.No.33: Why Nitrogen is diamagnetic and oxygen is paramagnetic?

Ans: According to M.O.T. Oxygen has two unpaired electrons in its degenerate orbital that’s 2.

While in case of nitrogen, it is diamagnetic because it does not have unpaired electrons.

Q.No.34: what is bond order?

Ans: the number of bonds formed between two atoms is called bond order. We can calculate bond order with help of following relationship.

Q.No.35: Why helium does not form Helium molecule ()?

Ans:Helium can not form molecule because its bond order is zero.

The  orbitals of two helium  orbitals are combined give 1s and is as shown in fig.

Q.No.36: What is bond energy? Also mention factors affecting Bond energy?

Ans: the amount of energy required to break all bonds of particular type  in one mole of substance is called bond energy.

It is measured in KJ/mol

Example:

  • Bond energy of  is 431 KJ/mol
  • Bind energy of  is 240 KJ/mol

Factors affecting bond energy:

  • Electro negativity difference of atoms  α                         B.E.
  • Size of atoms   α   1 / B.E.
  • Bond length          α          1 / B.E

Q.No.37: Difference between bonding molecular orbital’s and Anti-bonding molecular orbital’s?

Ans:

Sr.No.B.M.O.A.B.M.O
 The orbital which is formed by the reinforcing of electron waves is called bonding molecular orbitalsThe orbital which is formed by the canceling of electron waves is called anti bonding molecular orbital
 Its energy is less than its parent orbitalIts energy is greater than its parent orbital
 σ and π are example of bonding molecular orbitalsσ and π are example of anti-bonding molecular orbitals

Q.No.38:what do you meant by dipole moment?

Ans: the cross product of electric charge and distance between opposite charge is called dipole moment.

Mathematical form

                        µ          =         q  ×  r

Units:

There are two units od dipole moments

  • DeyBe
  • Colum Meter

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  1. Good effort

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