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.
Document Preview
Extracts from the notes are below, to see the PDF you'll receive please use the links above
CHAPTER 2
STRUCTURE OF ATOM
• Atom is the smallest indivisible particle of the matter
...
PARTICLE
ELECTRON
PROTON
NEUTRON
Sir
...
J
...
6 x 10 Coloumb 1
...
11 x 10-31kg
1
...
67492 x10-27kg
Mass
Electrons were discovered using cathode ray discharge tube experiment
...
Cathode ray discharge tube experiment: A cathode ray discharge tube madeof
glass is taken with two electrodes
...
These rays were called cathode rays
...
Cathode rays consist of negatively charged electrons
...
Cathode rays themselves are not visible but their behavior can be
observed with
help of fluorescent or phosphorescent materials
...
In absence of electrical or magnetic field cathode rays travel in
straight lines
d
...
The characteristics of the cathode rays do not depend upon the
material of the electrodes and the nature of the gas present in the cathode ray
tube
...
The chargeto
mass ratio of an electron as 1
...
The value of the charge on an electron is -1
...
The mass on an electron was determined by combining the results
ofThomson’s experiment and Millikan’s oil drop experiment
...
1094 x 10-31kg
...
Characteristics of positively charged particles:
a
...
The positively charged particles depend upon the nature of gas present in the
cathode ray discharge tube
c
...
d
...
They are electrically neutral particles having a mass
slightly greater than that of the protons
...
Mass Number (A) :Sum of the number of protons and neutrons present in
thenucleus
...
An
important feature of Thomson model of an atom was that mass of atom
isconsidered to be evenly spread over the atom
...
Observations from α- particles scattering experiment by Rutherford:
a
...
A small fraction of α- particles got deflected through small angles
c
...
Since most of the α-particles passed through foil undeflected, it means most
of the space in atom is empty
b
...
Since only some of the α-particles suffered large deflections, the positively
charged mass must be occupying very small space
d
...
The nucleus
comprisesof protons and neutrons
...
Electrons and nucleus are held together by electrostatic forces
ofattraction
...
According to Rutherford’s model of atom, electrons which are negatively
charged particles revolve around the nucleus in fixed orbits
...
theelectrons undergo acceleration
...
Thus, an electron in an orbit should
emitradiation
...
But this does not happen
...
The model does not give any information about how electrons
aredistributed around nucleus and what are energies of these electrons
Isotopes: These are the atoms of the same element having the same
atomicnumber but different mass number
...
e g 18Ar40 , 20Ca40
Isoelectronic species: These are those species which have the same numberof
electrons
...
When
anelectrically charged particle moves under acceleration, alternating
electricaland magnetic fields are produced and transmitted
...
These waves are called
electromagneticwaves or electromagnetic radiations
...
Oscillating electric and magnetic field are produced by oscillating charged
particles
...
b
...
That means they can even travel in
vacuum
...
Wavelength: It may be defined as the distance between two
neighbouring crests or troughs of wave as shown
...
b
...
c
...
In vacuum all types of electromagnetic radiations travel with
thesame velocity
...
It is denoted by v
d
...
Velocity = frequency x wavelength c = νλ
Planck's Quantum Theoryo The radiant energy is emitted or absorbed not continuously but
discontinuously in the form of small discrete packets of energy called
‘quantum’
...
e
...
626 x 10 Js
o Energy is always emitted or absorbed as integral multiple of this
quantum
...
19
Black body: An ideal body, which emits and absorbs all frequencies, is calleda
black body
...
Photoelectric effect: The phenomenon of ejection of electrons from thesurface
of metal when light of suitable frequency strikes it is calledphotoelectric effect
...
Experimental results observed for the experiment of Photoelectric effecto When beam of light falls on a metal surface electrons are
ejectedimmediately
...
Thisis called threshold frequency
...
Photoelectric work function (Wo): The minimum energy required to
ejectelectrons is called photoelectric work function
...
e
...
whenever radiation
interacts with matter, it displays particle like properties
...
Spectrum is of two types: continuous and line spectrum
a
...
b
...
It has bright lines with dark spaces between them
...
It consists of a range
ofelectromagnetic radiations arranged in the order of increasing wavelengths
ordecreasing frequencies
...
Spectrum is also classified as emission and line spectrum
...
o Absorption spectrum is the spectrum obtained when radiation is
passedthrough a sample of material
...
The wavelengths which are absorbed are missing
and comeas dark lines
...
Spectral Lines for atomic hydrogen:
Rydberg equation
R = Rydberg’s constant = 109677 cm-1
Bohr’s model for hydrogen atom:
a
...
These paths are called orbits orenergy
levels
...
b
...
c
...
An electron can move only in those orbits for which its angularmomentum
is an integral multiple of h/2π
The radius of the nth orbit is given byrn =52
...
Bohr’s model failed to account for the finer details of the hydrogen
spectrum
...
Bohr’s model was also unable to explain spectrum of atoms containing
more than one electron
...
e
...
de Broglie’s
relation is
21
Heisenberg’s uncertainty principle: It states that it is impossible to
determine simultaneously, the exact position and exact momentum (or
velocity) of an electron
...
Heisenberg’s uncertainty principle rules out the existence of definite pathsor
trajectories of electrons and other similar particles
Failure of Bohr’s model:
a
...
b
...
Classical mechanics is based on Newton’s laws of motion
...
Reason: Classical mechanics ignores the concept of dual behaviour of matter
especially for sub-atomic particles and the Heisenberg’s uncertainty principle
...
Quantum mechanics is based on a fundamental equation which is
calledSchrodinger equation
...
Out of the
possible values, only certain solutions are permitted
...
Thus, we can say
that energy is quantized
...
The value of ψhas no physicalsignificance
...
It is called probability density
...
Quantum numbers: There are a set of four quantum numbers which specifythe
energy, size, shape and orientation of an orbital
...
Principal quantum number (n):It identifies shell, determines sizes and
energy of orbitals
Azimuthal quantum number (l): Azimuthal quantum number
...
l
...
e
...
For a
given value of n, it can have n values ranging from 0 to n-1
...
Subshell
s p
d f g
notation
Value of ‘l’
0 1
2 3 4
Number of
1 3
5 7 9
orbitals
Magnetic quantum number or Magnetic orbital quantum number (ml):
Itgives information about the spatial orientation of the orbital with respect
tostandard set of co-ordinate axis
...
For each value of l, ml = – l, – (l –1), – (l–2)
...
(l – 2), (l–1), l
Electron spin quantum number (ms): It refers to orientation of the spin of
theelectron
...
+1/2 identifies the
clockwisespin and -1/2 identifies the anti- clockwise spin
...
Radial nodes: Radial nodes occur when the probability density of wave
functionfor the electron is zero on a spherical surface of a particular radius
...
Number of angular nodes = l
Total number of nodes = n – 1
23
Degenerate orbitals: Orbitals having the same energy are called
degenerateorbitals
...
So, due to the screening effect, the net positive charge experienced by
theelectron from the nucleus is lowered and is known as effective nuclear
charge
...
Aufbau Principle: In the ground state of the atoms, the orbitals are filled
inorder of their increasing energies
24
n+l rule-Orbitals with lower value of (n+l) have lower energy
...
The order in which the orbitals are filled isas follows:
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 4f, 5d, 6p, 7s
...
Only two electrons may exist in the same
orbitaland these electrons must have opposite spin