Unit 1 and 18 Five Marks1

8/10/2019 Unit 1 and 18 Five Marks1

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GOOD LUCK TUITION CENTER FOR CHEMISTRY

1 GOOD LUCK TUITION CENTER OF CHEMISTRY

1. Discuss the Davisson and Germers experiment.

1. In 1927 Davission and Germer observed that a beam of electrons obtained from a heated

tungsten filament is accelerated by using a high positive potential.

2. When this beam of accelerated electrons is allowed to fall on a large single crystal of

Nickel, the electrons are scattered in different directions.

3. The diffraction pattern so obtained is similar to the diffraction pattern of Bragg's

experiment on diffraction of X-rays. Since X-rays have wave character, therefore the

electrons also must have wave character.

4. The wavelength of the electrons determined by diffraction experiment was

found to be in agreement with the values calculated from de - Broglie equation.

5. So, it is clear that an electron behaves as a wave.

2. Derive de-Broglies equation. What is its significance?

(i) de-Broglies equation:de-Broglies equation may be derived by combining mass energy

relationships proposed by Max Planck and Einstein.

1. According to Plancks quantum theory, photon is assumed to have wave character So,

E = hv (1)

where v = frequency of the wave, h = Plancks constant.

2. According Einstein equation, photon is supposed to have particle character So,

E = mc2 (2)

where m = mass of photon, c = velocity of light.

From equations (1) and (2), we get

hv = mc2, But v =

C

h

C= mc

2 =

mc

h


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3. The above equation is applicable to any material particle. the mass (m) of the photon is

replaced by mass of the material particle and velocity (c) of the photon is replaced by the

velocity (v) of the material particle.

=h

mv (or) =P

h

mv = P = momentum of the particle.

=P

his called de-Broglie equation and is called de Broglie wavelength

(ii) Significance:

1. Dual nature of matterfinds application in construction of electron microscope.

2. By electron diffractionused in the study of surface structure of solids.

3. This concept can be applied not only to electrons but also to smaller particles like

neutrons, protons and molecules etc.,

3. Discuss the shapes of s, p and d orbitals.

(i) Shape of s orbitals:

1. For s-orbitals, l = 0, m = 0. i.e., there is only one possible orientation.

2. All s-orbitals are non-directional.

3. Spherically symmetrical about the nucleus.

4. s-orbital is spherical in shape.

5. The number of nodes in s orbital is equal to (n-1).


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(ii) Shape of p-orbitals:

1. For p-orbitals l = 1, m = 1 i.e., m = -1, 0 and + 1.

2. p-orbitals can have three possible orientations. 2px 2py 2pz

3. Each p-orbital consists of two lobes symmetrical about a particular axis. Two lobes of

each p-orbital are separated by a nodal plane.

4. porbitals have dumb-bell shape and have directional character.

5. porbitals of higher energy level have similar shapes although their size are bigger.

(iii)Shape of d-orbitals:

1. For d-orbital, l = 2, m = 2, i.e2, 1, 0, +1, +2.

2. It meansdorbital can have five orientations.

3. They are represented as dxy dyz dzx dx2y

2and dz

2.

4. dxy, dyz and dzx orbitals have clover leaf shape.

5. The dz2

orbital is symmetrical about Zaxis and has a dumb-bell shape with doughnut

shaped electron cloud in the centre and dx2-y

2orbital is also clover leaf shaped but its

leaves are directed along the X and Y axis.

4. Briefly explain Molecular Orbital Theory.

1. In a molecule, electrons are present in new orbitals are called molecular orbitals.

2. Molecular orbitals are formed by the combination of atomic orbitals ofequal energies or

of comparable energies.

3. The number of molecular orbitals formed is equal to the number of atomic orbitals

undergoing combination.

4. Two atomic orbitals can combine to form two molecular orbitals.

* Lower energy orbitalBonding molecular orbital.

* Higher energy orbitalAntibonding molecular orbital.5. The shape of molecular orbitals depend upon the shapes of combining atomic orbitals.


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6. * Bonding molecular orbitals are represented as , and

* Antibonding molecular orbitals are represented as *, * and *

7. The molecular orbitals are filled in the increasing order of their energies, starting with

orbital of least energy. (Aufbau principle)

8. A molecular orbital can accommodate only two electrons and these two electrons must

have opposite spins. (Paulis exclusion principle).

9. While filling molecular orbitals of equal energy, pairing of electrons doesnot take place

until all such molecular orbitals and singly filled with electrons having parallel spin.

(Hunds rule).

5. Explain the formation of O2 molecule by Molecular Orbital Theory.

1. The electronic configuration of oxygen (Z=8) is 1s

2

2s

2

2p

4

.2. O2 molecule has 16 electrons.

3. These 16 electrons are filled in the molecular orbitals in the order of increasing energy.

Bond order: 2

i.e., Nb = 8, Na = 4 Bond order =8 - 4

2= 2

Thus, oxygen molecule has two bonds. i.e., O = O

4. Magnetic property: Paramagnetic in nature.


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6. Describe about the electronic configuration of molecule and its correction with

molecular behaviour.

(i) Stability of a molecule: From the electronic configuration, it is possible to find out the

number of electrons in bonding molecular orbitals (Nb) and number of electrons in

antibonding molecular orbitals (Na)

(i) If Nb > Na, the molecule is stable because influence of bonding electron is greater

than antibonding electrons

(ii) If Nb < Na, the molecule is unstable because influence of antibonding electron is

greater than bonding electrons

(iii) If Nb = Na, the molecule is unstable because influence of bonding electron is equlal

to antibonding electrons

(ii) Bond order: It is defined as half the difference between the number of electrons inNb and

the number of electrons inNa.

Bond order = 1/2 (NbNa)

1. If bond order is positive the molecule is stable. Nb > Na

2. If bond order is zero (or) negative the molecule is unstable. Nb Na

(iii) Stability of a molecule bond order

e.g. bond order 3 is more stable than bond order 2.

(iv) A chemical bond can be single, double or triple bond but cannot be a fraction.

(v) Bond length: Bond length is inversely proportional to the bond order. Greater the bond

order. Greater the bond order, shorter the bond length are viceversa.

(vi) Magnetic character of the molecule:

The molecule has paired electrondiamagnetic in nature.

The molecule has unpaired electronparamagnetic in nature.


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7. Explain the formation of N2 molecule by Molecular Orbital Theory

1. The electronic configuration of nitrogen (Z = 7) is 1s2

2s2

2p3.

2. N2 molecule has 14 electrons.

3. These 14 electrons are filled in the molecular orbitals in the order of increasing energy.

4. Bond order : 3

i.e., Nb = 8, Na = 2 Bond order =2

2-8= 3

N2 molecule has triple bond i.e. N = N

5. Magnetic property: Diamagnetic in nature.


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8. Write a note on hydrogen bonding.

Hydrogen bonding comes into existence as a result of dipoledipole interaction between

the molecule in which hydrogen atom is covalently bonded to a highly electronegative

atom

The conditions for the effective hydrogen bonding formation are :

High elecronegativity of the atom bonded to hydrogen atom so that bond is.

sufficiently polar

Small size of the atom bonded to hydrogen so that it is able to attract the bonding

electron pair effectively .

Types of hydrogen bonds

Intermolecular hydrogen bonding :

This type of hydrogen bond is formed between the two molecules of same or

different compound.

Example .

In the solid state ,hydrogen fluoride consists of long zig-zig chains of molecules associated

by hydrogen bond.There fore hydrogen fluoride is represented as (HF)n

Intramolecular hydrogen bonding :

This type of bond is formed between hydrogen atom and N, O,or F atom of the same

molecule.

This type of h;ydrogen bonding is commonly called chelation

This \bond is more frequently found in organic compounds.

Example

Onitor phenol Salicylic acid

Two problems

One based on uncertainity principle

One based on de broglie equaation


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Unit18 Carbonyl compounds

Mechanism in carbonyl compounds ( Three Mechanism )

Name reaction in carbonyl compounds

Reaction of acetone with dry HCl gas

Difference between acetaldehyde and acetone

Difference between formaldehyde and acetaldehyde

Difference between acetaldehyde and benzaldeyde

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Unit 1 and 18 Five Marks1