a projec on structure of atom with NCERT as reference

1. Akarshik Banerjee
Class- X l ’B’

2. In 1897, J.J. Thomson used a cathode ray
tube to deduce the presence of a negatively
charged particle: the electron.

3. Cathode rays have identical properties
regardless of the element used to produce
them. All elements must contain identically
charged electrons.
Atoms are neutral, so there must be
positive particles in the atom to balance the
negative charge of the electrons
Electrons have so little mass that atoms
must contain other particles that account
for most of the mass

4.  Eugen Goldstein in 1886 observed what
is now called the “proton” - particles
with a positive charge, and a relative
mass of 1 (or 1840 times that of an
electron)
 1932 – James Chadwick confirmed the
existence of the “neutron” – a particle
with no charge, but a mass nearly

5. Mass of
electron is
9.3 x 10-31
The oil drop
apparatus
1916 – Robert Millikan determines the
mass of the electron: 1/1840 the mass of
a hydrogen atom; has one unit of negative
charge

6. Particle
Charge
Mass (g)
Location
Electron
(e-)
-1
9.11 x 10-28
Electron
cloud
Proton
(p+)
+1
1.67 x 10-24
Nucleus
0
1.67 x 10-24
Nucleus
Neutron
(no)

7. Thomson believed that the
electrons were like plums
embedded in a positively
charged “pudding,” thus it
was called the “plum pudding”
Thomson’s model was cancelled out as
model.experiments of Rutherford it could not
explain the

8.  Alpha particles are helium nuclei - The
alpha particles were fired at a thin sheet
of gold foil
 Particles that hit on the detecting
screen (film) are recorded
 Most of the particles passed right throu
 A few particles were deflected
 VERY FEW were greatly deflected

9. The nucleus is small
The nucleus is dense
The nucleus is positively charged
Based on his experimental evidence:
The atom is mostly empty space
All the positive charge, and almost all the
mass is concentrated in a small area in the
center. He called this a “nucleus”
The nucleus is composed of protons and
neutrons (they make the nucleus!)
The electrons distributed around the
nucleus, and occupy most of the volume
His model was called a “nuclear model”
If the electrons revolved around nucleus in
fixed orbit then it would constantly loose energy
and finally collapse in the nucleus as per law of
electrodynamics. Then the atoms would be
highly unstable , but that is not so.. Thus

10. Electrons revolves around the nucleus in
fixed circular orbits .
During revolution there in no loss or gain
of energy. Energy change takes place only
when electron jumps.
In an atom only those orbits are possible
in which the angular momontum of an
electron is an integral multiple of nh/2
1. It was applicable to atoms containing only one electron.
2. It could not explain the splitting of spectral lines under electrical and
magnetic field.
3. It could not explain Heisenberg’s uncertainty principle.
4. It could not explain formation of molecule through bonding.

11. The principal energy levels found around the
nucleus where electrons revolve.
These are the sub energy levels found within
the shells.
These are the space around the nucleus where
probability of finding electron is maximum.
It states that electrons occupy shells subshells and
orbitals in increasing order of energy.
The half filled and full
filled orbitals are more
stable than the rest
orbitals.

12. It states that when two or more subshells of same energy
level are available then electron is first filled one by one in
them and then pairing takes place in opposite spin.
Quantum numbers describe values of conserved quantities in the
dynamics of the quantum system. Perhaps the most peculiar aspect
of quantum mechanics is the quantization of observable quantities.
This is distinguished from classical mechanics where the values can
range continuously. They often describe specifically the energies of
electrons in atoms, but other possibilities include angular
momentum, spin etc. Any quantum system can have one or more
quantum numbers, it is thus rigorous to list all possible quantum

13. number)
•The value of
ranges from 1 to "n", where "n" is the shell containing
the outermost electron of that atom. For example, in cesium (Cs), the
outermost valence electron is in the shell with energy level 6, so an
electron in cesium can have an
value from 1 to 6.
•The second, describes the subshell (0 = s orbital, 1 = p orbital, 2 = d
orbital, 3 = f orbital, etc.).(Azimuthal qn.)
•The value of
ranges from 0 to . This is because the first p orbital
(l=1) appears in the second electron shell (n=2), the first d orbital (l=2)
appears in the third shell (n=3), and so on. A quantum number beginning in
3,0,... describes an electron in the s orbital of the third electron shell of
an atom.
•The third, , describes the specific orbital (magnetic qn)(or "cloud") within
that subshell.
•The values of
range from
to . The s subshell (l=0) contains only
one orbital, and therefore the ml of an electron in an s subshell will
always be 0. The p subshell (l=1) contains three orbitals (in some systems,
depicted as three "dumbbell-shaped" clouds), so the ml of an electron in a
p subshell will be -1, 0, or 1. The d subshell (l=2) contains five orbitals,
with ml values of -2,-1,0,1, and 2.
•The fourth, , describes the spin of the electron within that orbital. (spin
qn)
•Because an orbital never contains more than two electrons,
will be
either
or , corresponding with "spin" and "opposite spin".
It states that no two electrons of an atom can have same set
of all four quantum numbers.

14. Radiations have both wave like and particle like nature. The particle like
nature can be proved by the following effects-
When monochromatic beam of radition is allowed to pass through a nicol prism
and the radition is aloowed to fall at a ZnS plate then formation of Scntillations
confirms then dual behaviour of radiation.
Einstine discovcred that it rasiation of a minimum Threshold frequency is
allowed to fall on the surface of an active metal then ejection of electrons from
the surface takes place called photoelectrons . The phenomenon is called
photoelectric effect. Thus light particles had momentum and also mass.

15. The work function is the minimum energy that must be
given to an electron to liberate it from the surface of
a particular substance. In the photoelectric effect,
electron excitation is achieved by absorption of a
photon. If the photon's energy is greater than the
substance's work function, photoelectric emission
occurs and the electron is liberated from the surface.
Matter also show dual
behavior. The wave like
nature of electron can
be proved through the
electron diffraction
experiment.

16. In quantum mechanics, the Heisenberg uncertainty principle states by
precise inequalities that certain pairs of physical properties, such as position
and momentum, cannot be simultaneously known to arbitrarily high
precision. That is, the more precisely one property is measured, the less
precisely the other can be measured.

17. According to Heisenberg's uncertainty principle, it is impossible to describe the
exact position of an electron at a given moment in terms of position, we can
speak of most probable regions where the probability of finding an electron in
the space around the nucleus of an atom is high. The electron does not always
remain at a fixed distance from a nucleus. It keeps moving in the whole space
around the nucleus but tends to remain most of the time within a small volume
around the nucleus, where the probability of locating the electron is maximum.
A new atomic model, was needed to explain
•Wave nature (dual character) of atoms.
•The idea of uncertainty in the position of electrons in a atom.
•Concept of fixed energy states.
Schrodinger put the wave model or quantum mechanical model of atom forward.
The behavior of an electron is defined by the mathematical representation:
where,
y = (psi) is a wave function of space coordinates 'x', 'y', 'z' and represents the amplitude of the electron wave.
m = mass of the electron
E = the total permissible energy level, which the electron can have.
V = potential energy of the electron given by ze2/r.
h = Planck's constant having the value 6.626 x 10-34 J s.
d= (delta)stands for infinitesimal change.
The wave length function y (psi) describes a number of possible states of an electron in an atom. Since a large number of solutions are
possible, four quantum numbers were introduced, which describe meaningful permissible values of energy and location with respect to
its nucleus.

18. According to probability
density the shapes of
electron clouds can be
drawn.
The space around the
nucleus where the
probability of finding an
electron is zero is called a
node.
Nodal Plane
The plane containing the
Nodal plane

19. It is the series of emission spectra
obtained when an electron jumps
from any higher shell to the first
shell.it falls under UV region and
value of n1=1.
It is the series of emission spectra
obtained when an electron jumps
from any higher shell to the second
shell.it falls under visible region
and value of n1=2.

20. It is the series of emission spectra obtained when an
electron jumps from any higher shell to the third
shell. It falls under IR region and value of n1=3.
It is the series of emission spectra obtained when an
electron jumps from any higher shell to the fourth shell.
It falls under IR region and value of n1=4.
It is the series of emission spectra obtained when an
electron jumps from any higher shell to the fifth shell.