Search for notes by fellow students, in your own course and all over the country.

Browse our notes for titles which look like what you need, you can preview any of the notes via a sample of the contents. After you're happy these are the notes you're after simply pop them into your shopping cart.

My Basket

You have nothing in your shopping cart yet.

Title: Structure of Atoms - Class 11
Description: These notes will help you master this concept and help you in exams. It is Class 11 level. A little bit advanced.

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above


CREATED BY – SANSKAR CHAUDHARY
CHEMISTRY CLASS 11
CHAPTER 2 - NOTES

CHAPTER 2 – STRUCTURE OF ATOM
Discovery of Electron
A cathode ray tube is made of glass containing two thin electrodes sealed in it
...
The pressure of different gases can be adjusted by evacuation
...
These are called cathode rays or cathode ray particles
...
Properties of cathode rays are :1
...

2
...

3
...

4
...

Thus, we can conclude that electrons are basic constituent of all the atoms
...
J
...
Thomson argued that the
amount of deviation of the particles from their path in the presence of electrical or magnetic
field :1
...

2
...

3
...

By carefully balancing the electrical and magnetic field strength, it is possible to bring back
the electron to the path followed as in the absence of electric or magnetic field
...
758820 × 1011 C kg-1
R
...
Milkman devised a method known as oil drop experiment to determine the charge on
the electrons
...
6 × 10-19 C
...
6022 × 10-19 C
...


Discovery of Protons
Electrical discharge carried out in the modified cathode ray tube led to the discovery of
particles carrying positive charge, also known as canal rays
...
The positively charged particles depend upon the nature of gas present in the
cathode ray tube
...
The charge to mass ratio of the particles is found to depend on the gas from which
these originate
...
Some of the positively charged particles carry a multiple of the fundamental unit of
electrical charge
...
The behaviour of these particles in the magnetic or electrical field is opposite to that
observed for electron or cathode rays
...

This positively charged particle was characterised in 1919
...
These particles were discovered by Chadwick (1932) by bombarding a
thin sheet of beryllium by α-particles
...
He named these particles as neutrons
...
00054
1
...
00867

Approx
...
J
...
The sphere was
positively charge while electrons were embedded in it
...

Proposed sphere had a radius of approximately 10-10m
...
It was able to explain the overall
neutrality of an atom, but was inconsistent with results of future experiments
...
The thin gold foil had a circular
fluorescent zinc sulphide screen around it
...
The observations of this experiment are as follows:
1
...

2
...

3
...
e
...

On the basis of the observations, Rutherford drew the following conclusions regarding the
structure of atom :1
...

2
...

3
...

On the basis of above observations and conclusions, Rutherford proposed the nuclear model
of the atom:
1
...

2
...

3
...


Some common terms in Chemistry
1
...
of protons in an atom = no
...
Mass number (A) = no
...
of neutrons (n)
3
...
Eg
...

4
...
Eg
...

5
...
Eg
...


Drawbacks of Rutherford’s Model of an Atom
Rutherford nuclear model of an atom is like a small scale solar system with the nucleus
playing the role of the massive sun and the electrons being similar to the lighter planets
...


When classical mechanics is applied to the solar system, it shows that the planets describe
well-defined orbits around the sun
...

However, when a body is moving in an orbit, it undergoes acceleration
...
According to the
electromagnetic theory of Maxwell, charged particles when accelerated should emit
electromagnetic radiation
...
The orbit will thus continue to shrink
...
But this
does not happen
...
If the
electrons were stationary, electrostatic attraction between the dense nucleus and the
electrons would pull the electrons toward the nucleus to form a miniature version of
Thomson’s model of atom
...
e
...


Wave nature of Electromagnetic Radiation
Energy from any source is emitted continuously in the form of radiation or waves
...
These radiations are called Electromagnetic Radiation
...
It is established that there are many types of
Electromagnetic Radiation
...
This is known as speed of light and is represented as ‘c’
...
Another commonly used quantity in
spectroscopy is wavenumber (̅)
...

̅

and


...
Arrangement
of all electromagnetic radiation in increasing order of their wavelength is given below
...


Photoelectric Effect
It is the phenomenon of ejection of electrons from a metal surface when a light of suitable
frequency strikes the metal
...
Also, Kinetic Energy of the ejected electron is directly proportional
to the frequency of radiation
...
If the striking
radiation has energy and minimum energy required to eject the electron (work function)
is
then Kinetic Energy of ejected electron is given by :-

Atomic Spectra
The spectrum of radiation emitted by a substance in excited state is called emission
spectrum
...
When
white light from any source is passed through a prism, it splits into seven colours
...
This is called continuous
spectrum
...
Isolated
bright coloured lines separated by dark bands are obtained
...

Each element has its own characteristic and unique Line Spectrum
...
When Electromagnetic Radiation is passed through certain
substances, we obtain spectrum in which dark lines are observed
...

This is known as Absorption Spectra
...
A series of spectral lines of hydrogen
atom is obtained
...

2
...

4
...


Lyman - Ultraviolet
Balmer - Visible
Paschen - Infrared
Brackett - Infrared
Pfund – Infrared

Rydberg Formula
Rydberg derived the formula for calculation of wavelength of various lines in the hydrogen
spectrum
...

is applicable to all systems where total number of electrons is 1
...
-


...


where z is the atomic number
...

Energy of photon,
where


...


Line Spectrum for Hydrogen
Series
Lyman
Balmer
Paschen
Brackett
Pfund

n1
1
2
3
4
5

n2
2,3,……
...

4,5,……
...

6,7,……
...
These are called Stationary State
...

2
...

4
...

Only those orbits are permissible whose angular momentum is an integral multiple of


...
When an electron jumps from one orbit to another orbit, then the difference
energy of two orbits is absorbed or radiated
...
Since the electrons revolve

only in fixed orbits, the electrons in an atom can have definite energy
...
This formula is also
where z is the atomic number
...


de-Broglie’s Hypothesis
de-Broglie proposed that like Electromagnetic Radiation, matter should also possess dual
wave-particle nature
...

He proposed the de-Broglie equation:-

This hypothesis is not applicable in daily life as macroscopic particles have very high mass so
their wavelength will be negligible
...



...
It has
no significance in our daily life as macroscopic objects have high mass
...
Hence for macroscopic objects, both position and momentum
can be defined with high accuracy
...

2
...

4
...

It fails to explain the spectrum of atoms other than H, Li2+ and He+
...

It fails to explain the splitting of spectral lines in presence of magnetic field (Zeeman
Effect) or electric field (Stark Effect)
...
The concept of orbit that was defined by Bohr model is not possible according to the
Heisenberg Uncertainty principle
...

1
...
The possible values of ‘n’ are 1,2,3,……∞
...
The maximum
number of electrons in a given principal energy level is 2n2 and maximum number of
orbitals associated with given principal quantum number is n2
...
Azimuthal Quantum Number (l): It describes the sub-energy level of the electron in
an atom
...
For a given value of ‘n’, ‘l’ can
take any value from 0 to (n-1)
...
Magnetic Quantum Number (m): The Magnetic Quantum Number determines the
number of orbitals in a subshell
...
Total values of ‘m’=(2l+1)
Subshell
l
m
Types
s
0
0
One s orbital
p
1
-1,0,1
Three p orbitals (py,py,pz)
d
2
-2,-1,0,1,2
Five d orbitals (dxy,dyz,dxz,
, )
f
3
-3,-2,-1,0,1,2,3
Seven f orbitals
4
...

Thus for a given value of ‘m’, only two values of ‘s’ are possible


...


Shapes of Atomic Orbitals
1
...
p-orbital

3
...

The energy of subshells of Hydrogen atom depend only on the Principal Quantum Number
...
The value of energy of orbitals of
other atoms depend on the value of ‘n’ and ‘l’ which is given by the ‘n+l’ rule
...
If value of ‘n+l’ is same, then electron goes to orbit
having less value of ‘n’
...
Pairing will always start with 4th electron in porbital, 6th electron in d-orbital and so on
...
If two
electrons have same value of ‘n’, ‘l’ and ‘m’ the they will have opposite spin
...


Magnetic Property
If all the electron in an atom are paired, it is called diamagnetic
...


Reasons for stability of Half-filled and Fully-filled orbitals
1
...
Hence they are more stable
...
High Exchange Energy : Electrons with same spin tend to exchange positions and
release certain amount of energy while doing so which is called exchange energy
...


Electronic Configuration of some elements

************************************THE END***********************************


Title: Structure of Atoms - Class 11
Description: These notes will help you master this concept and help you in exams. It is Class 11 level. A little bit advanced.