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ATOMIC STRUCTURE
Vikasana – Bridge Course 2012
HISTORY OF THE ATOM
The concept of an atom is originated from Greek philosophers i i t d f
G
k hil
h DEMOCRITUS & JOHN DALTON
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HISTORY OF THE ATOM
Democritus
Democritus studied the
nature of matter and the
constituents of all the
substances
HISTORY OF THE ATOM
In 1808,
1808 John Dalton put
John Dalton
forward
atomic theory to explain the laws
of chemical combination.
A
According
di to hi
him, an atom iis the
h
smallest unit of matter which
takes part in a chemical reaction.
He considered that atoms are
indivisible particles.
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w
Modern Concept of An
Atom was developed by
J J Th
J.J
Thomson , Goldstein,
G ld t i
Rutherford, Bohr and
other Scientists .
Modern Concept of An Atom was developed by
J.J Thomson , Goldstein, Rutherford, Bohr and other Scientists .
Vikasana‐ Bridge course 2012
Modern concept of an Atom
Atom consists of smaller
particles (sub atomic pparticles)
p
called Fundamental particles.
• Electron
El t
• Proton
• Neutron.
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Modern concept of an Atom
The atom contains nucleus at
its center,, which has positively
p
y
charged protons & neutral
neutrons.
Electrons are revolving
around the nucleus & they
carry –ve charge.
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ELECTRON(e‐)
ELECTRON(
J J Thomson discovered electron in 1897.
Mass of an Electron = 9.107x10-28 g
= 9.107x 10-31 kg
Charge of an Electron = Unit –ve
ve charge
= 1.602x10-19 coulombs
g of e- was measured byy R A Millikan in
The charge
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1939.
PROTON
E Goldstein discovered proton in 1836.
Mass of proton = 1.672x10
1 672x10-24 g
= 1.672x10-27 kg
Charge of proton = Unit +ve charge
= 1.602
1 602 x10-19
coulomb
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NEUTRON
James Chadwick discovered
neutron in 1932
Mass of neutron =1
1.675x10
675x10-24 g
=1.675x10-27 kg
C
Charge
off neutron = carry no charge
i.e. NEUTRAL
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ORBIT
Orbit is a well defined
circular path around the
nucleus in which an electron
revolves.
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Continued……
Orbit
O
bit off d
definite
fi it energy levels
l l called
ll d
shells.These shells are named as K,L,M and N
and
d numbered
b d as 11,2,3,
2 3 and
d 4 respectively
ti l
from the nucleus.
An orbit (shell) can accommodate electrons
equal to 2n2.
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Continued ……
For K Shell, n =1
maximum no of e-s in K shell =2n2
=2(1)2
=2
2
Therefore maximum no of electrons in K shell = 2
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Continued ……
Similarly ,
For L shell,, n = 2,, maximum no. of electrons = 08
For M shell,n
shell n =3,
3 maximum no.
no of electrons = 18
For N shell,n = 4, maximum no. of electrons = 32
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ORBITAL
Orbital is the three dimensional region around
the nucleus where the probability of finding
electron density is maximum.
All orbital have definite shape
p and each can
accommodate maximum of two electrons in it.
O bi l are namedd as s, p, d andd f.
Orbitals
f
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s orbital
Continued….
Shapes
p of Orbitals
p orbitals
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Continued….
d Orbitals
f Orbitalas
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Continued….
s orbital can accommodate 2 electrons. There are
three p orbital,, each can accommodate two
electrons therefore totally p orbital can
accommodate 6 electrons. There are five d orbital
so they can accommodate maximum of 10
y can
electrons and there are seven f orbital and they
accommodate14 electrons.
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ENERGY LEVEL
The relative energies of
various orbital can be shown
by an arrangement and is
called as
ENERGY LEVEL
diagram.
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Schematic diagram to
remember sequence of
filling electrons in
atomic orbitals
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ELECTRONIC CONFIGURATION
Distribution of electrons in
various orbital in the increasing
energy level is called as
electronic configuration.
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Electronic Configuration
Elements Symbol Atomic
No.
Hydrogen
H
1
Helium
He
2
Lithium
Li
3
Beryllium
Be
4
Boron
B
5
C
Carbon
C
6
Neon
Ne
10
No of
Electrons
1
2
3
4
5
6
10
Electronic
configuration
1s1
1s2
1s2 2s1
1s2 2s2
1s2 2s2 2p1
1s2 2s2 2p2
1s2 2s2 2p6
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Electronic Configuration
Elements
Symb Atomic
ol
NO.
No of
Electrons
Electronic
configuration
Sodium
Na
Magnesium Mg
11
12
11
12
1s2 2s2 2p6 3s1
1s2 2s2 2p6 3s2
Aluminium
Argon
g
Al
Ar
13
18
13
18
1s2 2s2 2p6 3s2 3p1
1s2 2s2 2p
p6 3s2 3p
p6
Potassium
K
19
19
1s2 2s2 2p6 3s2 3p6
4s1
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Electronic Configuration
Elements
Symb Atomic
ol
NO.
No of
Electrons
Electronic
configuration
1s2 2s2 2p6 3s2 3p6
4s2
1 2 2s
1s
2 2 2p
2 6 3s
3 2 3p
3 6
4s2 3d1
Calcium
Ca
20
20
S
Scandium
di
S
Sc
21
21
Vikasana – Bridge Course 2012