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ATOMIC STRUCTUREATOMIC STRUCTURE
Vikasana – Bridge Course 2012
HISTORY OF THE ATOMHISTORY OF THE ATOMHISTORY OF THE ATOMHISTORY OF THE ATOM
The concept of an atom is i i t d f G k hil h originated from Greek philosophers
DEMOCRITUS & JOHN DALTON
Vikasana – Bridge Course 2012
HISTORY OF THE ATOMHISTORY OF THE ATOMDemocritus
Democritus studied theDemocritus studied the nature of matter and the
constituents of all the substances
HISTORY OF THE ATOMHISTORY OF THE ATOMIn 1808 John Dalton putIn 1808, John Dalton put
forward atomic theory to explain the laws
John Dalton
atomic theory to explain the laws of chemical combination.
A di hi i hAccording to him, an atom is the smallest unit of matter which
takes part in a chemical reaction.He considered that atoms are
indivisible particles.Vikasana- Bridge course 2012
Modern Concept of AnModern Concept of AnModern Concept of An Atom was developed by J.J Thomson , Goldstein, Rutherford, Bohr and other Scientists .
Modern Concept of An Modern Concept of An Atom was developed by Atom was developed by J J Th G ld t iJ J Th G ld t iJ.J Thomson , Goldstein, J.J Thomson , Goldstein,
Rutherford, Bohr andRutherford, Bohr andRutherford, Bohr and Rutherford, Bohr and other Scientists .other Scientists .
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Modern concept of an AtomModern concept of an Atom
Atom consists of smaller particles (sub atomic particles)p p
called Fundamental particles.El t• Electron
• Proton• Neutron.
Vikasana – Bridge Course 2012
Modern concept of an AtomModern concept of an Atom
The atom contains nucleus at its center, which has positively , p ycharged protons & neutral neutrons.
Electrons are revolving around the nucleus & theyaround the nucleus & they carry –ve charge.
Vikasana – Bridge Course 2012
ELECTRONELECTRON((e‐))J J Thomson discovered electron in 1897.Mass of an Electron = 9.107x10-28 gg
= 9.107x 10-31 kgCharge of an Electron Unit ve chargeCharge of an Electron = Unit –ve charge
= 1.602x10-19 coulombsThe charge of e- was measured by R A Millikan in
Vikasana – Bridge Course 2012g y
1939.
PROTONPROTON
E Goldstein discovered proton in 1836. Mass of proton = 1 672x10-24 gMass of proton = 1.672x10 g
= 1.672x10-27 kgCharge of proton = Unit +ve charge
= 1 602 x10-19= 1.602 x10coulomb
Vikasana – Bridge Course 2012
NEUTRONNEUTRONNEUTRONNEUTRONJames Chadwick discovered
neutron in 1932Mass of neutron =1 675x10-24 gMass of neutron 1.675x10 g
=1.675x10-27 kgC fCharge of neutron = carry no charge i.e. NEUTRAL
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ORBITORBITORBITORBIT
Orbit is a well definedcircular path around thenucleus in which an electronrevolves.
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Continued……Continued……O bit f d fi it l l ll dOrbit of definite energy levels called
shells.These shells are named as K,L,M and N d b d 1 2 3 d 4 ti land numbered as 1,2,3, and 4 respectively
from the nucleus.An orbit (shell) can accommodate electrons
equal to 2n2.
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Continued ……Continued ……
For K Shell, n =1maximum no of e-s in K shell =2n2
=2(1)2
2=2Therefore maximum no of electrons in K shell = 2
Vikasana – Bridge Course 2012
Continued ……Continued ……
Similarly ,For L shell, n = 2, maximum no. of electrons = 08, ,
For M shell n 3 maximum no of electrons 18For M shell,n =3, maximum no. of electrons = 18
For N shell,n = 4, maximum no. of electrons = 32
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ORBITALORBITALOrbital is the three dimensional region around
the nucleus where the probability of findingelectron density is maximum.
All orbital have definite shape and each canpaccommodate maximum of two electrons in it.
O bi l d d d fOrbitals are named as s, p, d and f.
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Continued….Continued….Shapes of Orbitals Shapes of Orbitals pp
s orbitals orbital p orbitalsp orbitals
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Continued….Continued….d Orbitals f Orbitalasd Orbitals f Orbitalasd Orbitals f Orbitalasd Orbitals f Orbitalas
Vikasana – Bridge Course 2012
Continued….Continued….s orbital can accommodate 2 electrons. There are
three p orbital, each can accommodate two p ,electrons therefore totally p orbital can
accommodate 6 electrons. There are five d orbital so they can accommodate maximum of 10
electrons and there are seven f orbital and they can yaccommodate14 electrons.
Vikasana – Bridge Course 2012
ENERGY LEVEL ENERGY LEVEL The relative energies of
various orbital can be shown by an arrangement and is called as
ENERGY LEVEL diagram.diagram.
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Schematic diagram toSchematic diagram toSchematic diagram to Schematic diagram to remember sequence of remember sequence of filling electrons in filling electrons in atomic atomic orbitalsorbitals
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ELECTRONIC CONFIGURATIONELECTRONIC CONFIGURATION
Distribution of electrons in various orbital in the increasing
energy level is called asenergy level is called as electronic configuration.
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Electronic Configuration Electronic Configuration Elements Symbol Atomic No of ElectronicElements Symbol Atomic
No.No of
ElectronsElectronic
configurationHydrogen H 1 1 1s1Hydrogen H 1 1 1sHelium He 2 2 1s2
Lithium Li 3 3 1s2 2s1
Beryllium Be 4 4 1s2 2s2
Boron B 5 5 1s2 2s2 2p1
C C 2 2 2Carbon C 6 6 1s2 2s2 2p2
Neon Ne 10 10 1s2 2s2 2p6
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Electronic Configuration Electronic Configuration Elements Symb
olAtomic
NO.No of
ElectronsElectronic
configurationSodium Na 11 11 1s2 2s2 2p6 3s1
Magnesium Mg 12 12 1s2 2s2 2p6 3s2
Aluminium Al 13 13 1s2 2s2 2p6 3s2 3p1
Argon Ar 18 18 1s2 2s2 2p6 3s2 3p6g p pPotassium K 19 19 1s2 2s2 2p6 3s2 3p6
4s1
Vikasana – Bridge Course 2012
Electronic Configuration Electronic Configuration Elements Symb
olAtomic
NO.No of
ElectronsElectronic
configurationCalcium Ca 20 20 1s2 2s2 2p6 3s2 3p6
4s2
S di S 21 21 1 2 2 2 2 6 3 2 3 6Scandium Sc 21 21 1s2 2s2 2p6 3s2 3p6
4s2 3d1
Vikasana – Bridge Course 2012