Basic Atomic Structure...all in one... Very Specific....

1. Atomic Structure
….a brief overview…..

2. Important Highlights
• INTRODUCTION
• RUTHERFORD’S ATOMIC MODEL
• BOHR’S ATOMIC MODEL
• DISTRIBUTION OF EXTRA-NUCLEAR
ELECTRONS IN SHELLS & SUB-SHELLS
• ELECTRONIC CONFIGURATION OF ATOM
• WAVE-NATURE OF AN ATOM
• ATOMIC NUMBER
• MASS NUMBER BESU SHIBPUR,HOWRAH

3. Introduction
• ATOM : An atom is the smallest particle of an element, which
 Can not be subdivided.
 Does not exist in free state. But,
 Participate in chemical reaction.
The structure of an atom can be broadly divided into two parts
 Nuclear Parts
 Extra-Nuclear Parts
Nuclear part basically consist of 2 major particles– protons &
neutrons. Apart from this there are some more tiny particles
such as deuteron, neutrino, positron etc.
Extra-Nuclear parts consists of mainly electrons.
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4. Rutherford’s Atomic Model
• Also known as “Planetary Model” of Atom.
K e y F e a tu re s :
• An atom consists of a central nucleus. This nucleus is
composed of positively charged protons, and electrically
uncharged (neutral) neutrons.
• Negatively charged electrons revolve around the nucleus
in definite orbits.
• The orbits themselves can be at any distance from the
nucleus.
• In any atom, the number of protons is equal to the number
of electrons, and hence it is electrically neutral.
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5. Drawbacks of Rutherford’s Model
• It could not explain the stability of the atom. A/c to
classical theory of mechanics, during uniform revolution, any
body accelerates, & an accelerating charged particle must
emit radiation, and lose energy. Due to the fact, the electron
must emit radiation and lose energy. As a result, the
electron will follow a spiral path, and ultimately fall into
nucleus .So, Rutherford has given concept of unstable atom.
• The Rutherford’s model of atom does not say anything about
the arrangement of electrons in an atom.
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7. Bohr’s Atomic Model
The main points of Bohr’s atomic model are….
• Electrons revolve around the nucleus in orbits that have
fixed radius and energy. So, such orbits are also known
as stationary orbit ,Energy shells etc.
• The energy of the orbit is related to its size. The lowest
energy is found in the smallest orbit and its vice-versa.
• Radiation is absorbed or emitted when an electron jumps
from one orbit to another.
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8. Bohr postulated that the angular momentum of the electron is
quantized as shown…
Where, h=6.626*10^(-34) Js
Then by using simple physical equation he deduced the
expression for energy,velocity,radius,wavelength,wave-no. etc.
 L=nh/2ᴨ= mvr
 F= Ze*e/r*r=mv*v/r
 Where,L=Angular accn., Z=Atomic number, v=Orbital velocity
m=mass of electron, n=Principal Quantum Number
r=Radius of Orbit, h=Planck’s constant=6.626*10^34Js
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9. Deduced Formulae:
• Radius, r= (n^2/Z)*0.529 Å
• Energy, E= -(Z^2/n^2)* 13.6 eV
• Wave No.=1/wave-length=R(1/nf2-1/ni2)
• Velocity, v=(Z/n)*21.88*10^5 m/s
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10. e.g. Emission of a Quantum:1st Balmer Transition
-3.4eV
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11. Limitation of Bohr’s Atomic Model
• The Bohr atomic model is applicable only for one-electron
system. e.g. H, He+, Li++, Be+++ etc.
• The Bohr Model provides an incorrect value for the ground
state orbital angular momentum.
• It does not predict the relative intensities of spectral lines.
• The Bohr Model does not explain fine structure and hyperfine
structure in spectral lines.
• It violates the Heisenberg Uncertainty Principle because it
considers electrons to have both a known radius and orbit.
• It does not explain the Stark’s & Zeeman’s Effect.
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12. Concept of shells and subshells
• Shells, n, represents the distance of an electron from
Nucleus. It is represented by K,L,M,N,O,…for n=1,2,3,4,..
• Shell no., n, also represents the maximum no. of electrons
accommodated by a particular shell, which is 2n(2). i.e. for
n=1, First Shell, maximum no. of electrons=2.
Similarly, for n=2, it’s 8.
n=3, it’s 18 and so on.
• Subshell represents the traversal path of any electron in
3D view or, shape of the Orbital. For any Orbit ,n, it’s
value ranges from 0 to(n-1). It is represented by s,p,d,f,…
for l=0,1,2,3,…
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13. Quantum Numbers of Wave funtions
Quantum # Symbol Values Description
Principal n 1,2,3,4,… Size & Energy of orbital
Angular l 0,1,2,…(n-1) Shape of orbital
Momentum for each n
Magnetic ml -l…,0,…+l Relative orientation of orbitals within
for each l same l
Spin ms +1/2 or –1/2 Spin up or Spin down
Angular Momentum Quantum # l Name of Orbital
0 s (sharp)
1 p (principal)
2 d (diffuse)
3 f (fundamental)
4 g
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14. Electronic Configuration
The electrons gather around the nucleus in quantum orbitals
following four basic rules, called the Aufbau principle.
• no two electrons in the atom will share the same four quantum
numbers n, l, m, and s. (Pauli’s Exclusion Principle)
• electrons will first occupy orbitals of the lowest energy level.
• orbitals will be filled with the same spin number until all the
orbitals are filled, before it will begin to fill in the opposite spin.
(Hund’s Rule of maximum multiplicity)
• (n+l) Rule: electrons will fill orbitals by the sum of the
quantum numbers n and l. In case equal values of (n+l), orbitals
with the lower value of n, will be filled first.
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15. Electronic Configuration contd.
Hence, Aufbau Principle  Gives order of filling of electrons in
different subshells. It can be shown as follows….
• 1s2
• 2s22p6
• 3s23p63d10
• 4s24p64d104f14
• 5s25p65d105f14(5g18)
• 6s26p66d106f14(6g18)(6h22)
• 7s27p67d106f14(6g18)(6h22)(7i26)
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16. Electronic Configuration contd.
• The electronic configuration of elements generally follows
Aufbau principle.
• except some cases viz. Cu,Cr type d-block elements(due
to some stability factor).
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17. Wave Nature of an Atom
• Wave–particle duality postulates that, all particles exhibits
both particle as well as wave characteristics.
• Louis-Victor de Broglie describes the atom considering
"Dual Properties of Matter”.
• He formulated a hypothesis, claiming that all matter, not just
light, has a wave-like nature; he related wavelength (denoted
as λ), and momentum (denoted as p):
λ =h/p
This is the generalization of Einstein’s and Planck’s Equation.
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18. Atomic Number
• Atomic Number, Z: The number of protons in an atom.
• As atoms are neutral,
So,
N(p)=N(e)=Z
Where,
 N(p)= number of protons
 N(e)=number of electrons
 Z=Atomic Number
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19. Mass Number
Mass Number: The total numbers of neutrons and
protons in an atom.
So, if we know mass no. and atomic number, we can
find out the number of neutrons in an atom .
Mass Number - Atomic Number=Number of neutrons
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20. Notation of an Atom
Mass Number
65
Cu
29
Atomic Number
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21. References…...
• http://www.answers.com/topic/electron-configuration
• http://www.sparknotes.com/chemistry/fundamentals/atomicstr
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22. Thanking You…!
Presented By………
Navin Kumar
COMPUTER SCIENCE & TECHNOLOGY
BENGAL ENGINEERING & SCIENCE UNIVERSITY SHIBPUR, HOWRAH
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23. ….question please….!!
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