ATOMIC STRUCTUREATOMIC STRUCTURE

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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

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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

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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.

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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.

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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

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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

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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

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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

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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.

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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

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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

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