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Atomic Structure and Periodic Table

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What are we going to learn ? Part 1: Atomic structure

Historical background Dalton Thomson Rutherford/ Bohr

Inside the atom Orbits and sub-orbits Atomic number and Atomic mass Electron configuration of elements

Part 2: Periodic Table

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Part 1 : Atomic structure

Historical background

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Dalton’s atomic theory

John Dalton, English scientist Matter is made up of atoms All atoms of an element have the same

mass and the same properties Atoms are indestructible Atoms combine to form compounds

The main deficiency in Dalton’s theory was that the atom was considered indivisible. It could not explain concepts like charge, electromagnetism, radiation etc.

John Dalton 1766 - 1844

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Fluroscent screen

Glass tube filled with gas under low pressure

Positive and negative plates generating electric field

High voltage source (10000V)

CathodeëAnode

The discovery of the internal structure of the atom: Cathode Ray Tube

The scientist J.J.Thomson answered these questions

Experiments using electric discharge tube and cathode ray tube helped in discovering the internal structure of an atom

It was observed that the ray emanating from the cathode would deviate under the influence of electric field between the positive and negative plates

Why should this happen? Was it because the ray was made of light waves? the ray was made of positive particles? the ray was made of negative particles?

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Thomson stated that Cathode rays are a stream of particles

(electrons) ; not light rays Considering their deviation these

particles must be negatively charged.

Thomson’s atomic model

Thomson’s atomic model Atoms are positively charged spheres Electrons are microscopic constituents of

atoms Negatively charged electrons are

embedded in the atom like seeds of a water melon

The scientist Ernest Rutherford answered these questions

J.J.Thomson 1856 - 1940

But more doubts emerged ! How do we know that the atom is solid ? How are positive charges distributed in the atom ? Why are electrons the only particles coming out of atoms ?

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Rutherford’s experimentThin gold foil

Polonium

Alpha particle detector screen Box lined with Lead

Alpha ray Rutherford fired alpha particles at high velocity on a thin gold foil

Alpha particles: Minute positively charged particles. Their source : Polonium

Thickness of gold foil 1/50000 cm Out of approx. 20000 alpha particles

about 19990 passed through the foil without deviation ;

nine particles were scattered in various directions;

only one particle took a U turn and deviated by almost 180 degrees

Questions ! Questions ! If the atom was solid would most alpha particles have gone through the foil without deviating ?If positive particles were distributed uniformly inside the atom would only nine alpha particles have been scattered ? Only one alpha particle seems to have collided against a solid part of the atom and come right back. Would this solid part be smaller or larger compared to the size of

the atom?

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Rutherford’s planetary model of the atom The mass and positive charge of an

atom are concentrated in the centre (called as nucleus)

Negatively charged electrons revolve around the nucleus in circular or elliptical orbits just like the planets which orbit around the sun

The atom is largely hollow Atomic radius is 10-8 cm while the

radius of the nucleus is only 10-13 cm i.e 100000 times smaller than atomic radius.

Nucleus

Electron

The scientist Niels Bohr further improved this model by stating that electrons can only occupy ‘allowed’ orbits whose energy levels are stable

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Progressive changes in the understanding of the atom

Dalton (1808) The smallest indivisible particle of an element

Thomson (1897) negatively charged electrons embedded in a positively charged solid sphere

Rutherford (1911) Planetary model. Negatively charged electrons orbiting around extremely small positively charged solid nucleus

Bohr (1913) Electrons can occupy only ‘allowed’ orbits having stable energy levels

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Inside the atom

Part 1: Atomic structure (contd)

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Inside the atom The fundamental particles

The nucleus contains Z number of positively charged protons Z is called the atomic number

The nucleus contains N number of chargeless neutrons A = Z + N is called the atomic mass number

Negatively charged electrons rotate around the nucleus in orbits (or shells)

XA

Z

Mass number

Atomic number

Symbol of the element

H1

1Protons = ?

Electrons = ?

Neutrons = ?

Ca4020Na23

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The convention of indicating the atomic number and mass number of an element

Protons = ?

Electrons = ?

Neutrons = ?

Protons = ?

Electrons = ?

Neutrons = ?

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Inside the atom Fundamental particles

The attraction between positively charged nucleus and negatively charged electrons keeps the electrons within the atom

An orbit with orbit number ‘n’ can contain maximum 2n2

electrons In neutral atoms the number of protons is equal to the number

of electrons Protons and neutrons have the same mass (1.6 x 10–24 gm) The mass of an electron is 1837 times less than that of a proton The chemical properties of an element depend upon the

electrons in the outermost orbit

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Inside the atom Orbit, sub-orbit and energy levels

Electrons can orbit around the nucleus only in ‘allowed’ orbits

These orbits contain circular and elliptical sub-orbits

Sub-orbits are named as : s, p, d, f, g… s circular, p elliptical, d more elliptical,…

The energy level of elliptical sub-orbits is greater than that of the circular sub-orbit

In every orbit, electrons in s sub-orbit have the least energy level, electrons in p sub-orbit have a little more energy and so on

Es < Ep < Ed < Ef …

The number of sub-orbits in an orbit are equal to the number of the orbit

First orbit has 1 sub-orbit (called s) Second orbit has 2 sub-orbits (s, p) Third orbit has 3 sub-orbits (s, p, d)

3S

2P

2SNucleus

1S

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Inside the atom Orbits, sub-orbits and the number of electrons

Orbit No. Number of sub-orbits

Names of sub-orbits

Maximum Number of electrons in the sub-orbits

Maximum number of electrons in the orbits

1 1 1s 2 2

2 2 2s2p

26

8

3 3 3s3p3d

2610

18

4 4 4s4p4d4f

26

1014

32

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Inside the atom Shapes of sub-orbits

S sub-orbit p sub-orbit

d sub-orbit

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Inside the atom Electron configuration of elements

Rules1. S sub-orbit: max 2

electrons, p sub-orbit: max 6, d sub-orbit: max 10…

2. The sub-orbit with the least energy ‘1s’ is filled firstå

3. Thereafter electrons occupy the remaining sub-orbits in the order of increasing energy levels

4. The order of increasing energy is as shown

5s

4s

3s

2s

1s

2p

3p

4p

3d

4d

En

ergy

En

ergy

Shouldn’t 3d have come after 3p? Is there something

wrong?

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Inside the atom Electron configuration of elements - Hydrogen

1s 2s 2p 3s

H11

1s1

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Inside the atom Electron configuration of elements - Helium

1s 2s 2p 3s

He

2

4

1s2

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Inside the atom Electron configuration of elements - Lithium

Li3

7

1s 2s 2p 3s

1s2, 2s1

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Inside the atom Electron configuration of elements - Beryllium

1s 2s 2p 3sBe4

9

1s2, 2s2

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Inside the atom Electron configuration of elements - Boron

B5

11

1s 2s 2p 3s

6

5

1s2, 2s2, 2p1

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Inside the atom Electron configuration of elements - Carbon

C6

12

1s 2s 2p 3s

66

1s2, 2s2, 2p2

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Inside the atom Electron configuration of elements- Nitrogen

N7

14

1s 2s 2p 3s

77

1s2, 2s2, 2p3

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Inside the atom Electron configuration of elements- Oxygen

O8

16

1s 2s 2p 3s

88

1s2, 2s2, 2p4

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Inside the atom Electron configuration of elements - Fluorine

F9

19

1s 2s 2p 3s

10

9

1s2, 2s2, 2p5

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Inside the atom Electron configuration of elements - Neon

Ne10

20

1s 2s 2p 3s

1s2, 2s2, 2p6

10

10

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Inside the atom Electron configuration of elements–Sodium,Chlorine, Argon, Potassium, Calcium, Scandium

Na11

231s 2s 2p 3s 3p 4s 3d

Cl17

35

Ar18

40

K19

39

Ca20

40

Sc21

45

..

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Inside the atom Isotopes

Isotopes : Atoms of an element with the same atomic number but different mass number In other words the number of protons is equal but the

number of neutrons varies

H1

1Hydrogen

H2

1Deuterium

H3

1 Tritium

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Atomic structure What have we learnt ?

The nucleus contains positively charged protons and chargeless neutrons Protons and neutrons have equal mass Atomic number Z = Number of protons in the nucleus Mass Number A = Number of protons + neutrons

Negatively charged electrons rotate around the nucleus in ‘allowed’ orbits with stable energy levels

In neutral atoms the number of electrons and protons is equal The mass of an electron is 1837 times less than that of a proton The n th orbit can contain maximum 2n2 electrons

Orbits contain circular (s) and elliptical (p, d, f, g…) sub-orbits The n th orbit contains n sub-orbits

Energy level of elliptical sub-orbits is more than that of circular sub-orbits s sub-orbit has the least energy ; p sub-orbit has a little more and so on.

Es < Ep < Ed < Ef …

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Atomic structure What have we learnt ?

Electron configuration of elements As atomic number increases electrons in atoms occupy various orbits/-

sub-orbits Rules of electron configuration

Max 2 electrons in s sub-orbit, max 6 in p sub-orbit and so on 1s , the sub-orbit with the least energy level, is filled first Thereafter remaining sub-orbits are filled in the order of increasing

energy level The order of sub-orbits with increasing energy levels is : 1s, 2s, 2p, 3s,

3p, 4s, 3d, 4p, 5s, 4d, 5p…

H : 1s1 1

1

B : 1s2, 2s2, 2p15

11O : 1s2, 2s2, 2p4 8

16

Na : 1s2, 2s2, 2p6, 3s1 11

23K : 1s2, 2s2, 2p6, 3s2, 3p6, 4s1

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Part 2

Periodic tableBased on our knowledge of electron configuration of elements we shall

see how the elements can be logically ordered

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Periodic table

Periods :Seven rows

In each period the chemical properties of elements change progressively from left to right

Group: Eighteen columns

Properties of elements in the same group have some similarities

1

2

3

4

5

6

7

1

2

3 4 5 6 7 8 9 10

11

12

13 14

15

16 17

18

Periodic table : Arrangement of elements according to their increasing atomic numbers

PeriodGroup

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Periodic table Periods

1

2

3

4

5

6

7

1

2

3 4 5 6 7 8 9 10

11

12

13 14

15

16 17

18• Period 2 and 3 : Short periods

• Each contains 8 elements• Period 4 and 5 : Long periods

• Each contains 18 elements

• Period 6: Extra long period

• 32 elements

• After Lanthanum (La) fourteen elements are shown separately at the bottom

• Period 7 : 32 elements

• Many of these elements are man-made and short-lived

• After Actinide (Ac) 14 elements are shown separately at the bottom

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Periodic table Alkali metals (Group 1)

1

2

3

4

5

6

7

1

2

3 4 5 6 7 8 9 10

11

12

13 14

15

16 17

18• 1 electron in outermost orbit• Good reducing agents• React with water and release Hydrogen

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Periodic table Alkaline earth metals (Group 2)

1

2

3

4

5

6

7

1

2

3 4 5 6 7 8 9 10

11

12

13 14

15

16 17

18

• Two electrons in outermost orbit• Fairly good reducing agents• They release CO2 when their carbonate compounds are heated

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Periodic table Transition elements and other metals

1

2

3

4

5

6

7

1

2

3 4 5 6 7 8 9 10

11

12

13 14

15

16 17

18 Transition elements • Metallic properties reduce from left to right

Other metals

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Periodic table Non-metals and metalloids

1

2

3

4

5

6

7

1

2

3 4 5 6 7 8 9 10

11

12

13 14

15

16 17

18

Metalloids

Non-metals

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Periodic table Halogens (Group 17)

1

2

3

4

5

6

7

1

2

3 4 5 6 7 8 9 10

11

12

13 14

15

16 17

18

Halogens •7 electrons in the outermost orbit• Good oxidising agents

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Periodic table Inert gases (group 18)

1

2

3

4

5

6

7

1

2

3 4 5 6 7 8 9 10

11

12

13 14

15

16 17

18

• Outer orbits are fully filled with electrons• Chemically inactive

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Periodic table Classification according to external sub-orbit of atom

1 H

2 He

3 Li

4Be

5B

6C

7N

8O

9F

10Ne

11Na

12Mg

13Al

14Si

15P

16S

17Cl

18Ar

19K

20Ca

21Sc

22Ti

23V

24Cr

25Mn

26Fe

27Co

28Ni

29Cu

30Zn

31Ga

32Ge

33As

34Se

35Br

36Kr

37Rb

38Sr

39Y

40Zr

41Nb

42Mo

43Tc

44Ru

45Rh

46Pd

47Ag

48Cd

49In

50Sn

51Sb

52Te

53I

54Xe

55Cs

56Ba

57- 71

72Hf

73Ta

74W

75Re

76Os

77Ir

78Pt

79Au

80Hg

81Tl

82Pb

83Bi

84Po

85At

86Rn

87Fr

88Ra

89 - 103

104Rf

105Db

106Sg

107Bh

108Hs

109Mt

110Uun

111Uuu

112Uub

113Uut

114Uuq

115Uup

116Uuh

117Uus

118Uuo

57La

58Ce

59Pr

60Nd

61Pm

62Sm

63Eu

64Gd

65Tb

66

Dy

67Ho

68Er

69Tm

70Yb

71Lu

89Ac

90Th

91Pa

92U

93Np

94Pu

95Am

96Cm

97Bk

98Cf

99Es

100Fm

101Md

102No

103Lr

S Blockû D BlockP Blockû f Block

1

7

6

5

4

3

2

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4s

3s

2s

1s

2p

3p

3d

En

ergy

En

ergy

H He

Li Be B C N O F Ne

Na Mg Al Si P S Cl Ar

K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr

Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe

Cs Ba Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn

Fr Ra

La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb

Ac Th Pa U

Periodic table Electron configuration

S block d block p block

f block

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Periodic table: What have we learnt ? Periodic table : Arrangement of elements in the order of their

atomic number Contains 18 columns (called ‘Groups’) and 7 rows (called

‘Periods’) Elements in the same group have similar chemical properties

First group: Alkali metals (Good reducing agents) Second group: Alkaline earth metals (Fairly good reducing agent) Seventeenth group: Halogens (Good oxidising agents) Eighteenth group : Inert gases

In a period, as you go from left to right, metallic properties reduce while non-metallic properties increase å

Second and third period : Short periods (8 elements) Fourth and fifth periods : Long periods (18 elements) Sixth and seventh period : Extra long period (32 elements)

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The End