1. Atomic Structure and Periodic Table

2. 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

3. Part 1 : Atomic structure
Historical background

4. 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

5. The discovery of the internal structure of the atom: Cathode Ray Tube
Fluroscent screen
Glass tube filled with gas under low pressure
Positive and negative plates generating electric field
High voltage source (10000V)
Cathodeë
Anode
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?
The scientist J.J.Thomson answered these questions

6. Thomson’s atomic model
J.J.Thomson
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 ?
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
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

7. Rutherford’s experiment
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?
Thin 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 alpha particles
about 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

8. 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 cm i.e 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

9. Progressive changes in the understanding of the atom
Bohr (1913) Electrons can occupy only ‘allowed’ orbits having stable energy levels
Rutherford (1911) Planetary model. Negatively charged electrons orbiting around extremely small positively charged solid nucleus
Dalton (1808) The smallest indivisible particle of an element
Thomson (1897) negatively charged electrons embedded in a positively charged solid sphere

10. Part 1: Atomic structure (contd)
Inside the atom

11. 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)
The convention of indicating the atomic number and mass number of an element X A Z
Mass number
Symbol of the element
Atomic number Ca 40 20 H 1 Na 23 11
Protons = ?
Electrons = ?
Neutrons = ?
Protons = ?
Electrons = ?
Neutrons = ?
Protons = ?
Electrons = ?
Neutrons = ?

12. 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

13. Inside the atom Orbit, sub-orbit and energy levels2P 2S
Nucleus 1S
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)

14. 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 1s 2
2s 2p
2 6 8 3
3s 3p 3d
2 6 10 18 4
4s 4p 4d 4f
10 14 32

15. Inside the atom Shapes of sub-orbits
S sub-orbit
p sub-orbit
d sub-orbit

16. Inside the atom Electron configuration of elements
Shouldn’t 3d have come after 3p? Is there something wrong?
Inside the atom Electron configuration of elements
Rules
S sub-orbit: max 2 electrons, p sub-orbit: max 6, d sub-orbit: max 10…
The sub-orbit with the least energy ‘1s’ is filled firstå
Thereafter electrons occupy the remaining sub-orbits in the order of increasing energy levels
The order of increasing energy is as shown 4d
Energy 5s 4p 3d 4s 3p 3s 2p 2s 1s

17. Inside the atom Electron configuration of elements - Hydrogen1 1s 2s 2p 3s
1s1

18. Inside the atom Electron configuration of elements - Helium2 4 1s 2s 2p 3s
1s2

19. Inside the atom Electron configuration of elements - Lithium3 7 1s 2s 2p 3s
1s2, 2s1

20. Inside the atom Electron configuration of elements - Beryllium2p 3s Be 4 9
1s2, 2s2

21. Inside the atom Electron configuration of elements - Boron2p 3s B 5 11 6 5
1s2, 2s2, 2p1

22. Inside the atom Electron configuration of elements - Carbon2p 3s C 6 12 6
1s2, 2s2, 2p2

23. Inside the atom Electron configuration of elements- Nitrogen2p 3s N 7 14 7
1s2, 2s2, 2p3

24. Inside the atom Electron configuration of elements- Oxygen2p 3s O 8 16 8
1s2, 2s2, 2p4

25. Inside the atom Electron configuration of elements - Fluorine2p 3s F 9 19 10 9
1s2, 2s2, 2p5

26. Inside the atom Electron configuration of elements - Neon2p 3s Ne 10 20 10
1s2, 2s2, 2p6

27. Inside the atom Electron configuration of elements–Sodium,Chlorine, Argon, Potassium, Calcium, Scandium . . 1s 2s 2p 3s 3p 4s 3d Na 11 23 Cl 17 35 Ar 18 40 K 19 39 Ca 20 40 Sc 21 45

28. Inside the atom Isotopes2 1
Deuterium H 3 1
Tritium H 1
Hydrogen
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

29. 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 …

30. 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
B : 1s2, 2s2, 2p1 5 11
O : 1s2, 2s2, 2p4 8 16
Na : 1s2, 2s2, 2p6, 3s1 11 23
K : 1s2, 2s2, 2p6, 3s2, 3p6, 4s1 19 39

31. Part 2
Periodic table
Based on our knowledge of electron configuration of elements we shall see how the elements can be logically ordered

32. Periodic table Periods : Seven rows Group: Eighteen columns
Periodic table : Arrangement of elements according to their increasing atomic numbers 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
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
Group
Period

33. Periodic table Periods
Period 6: Extra long period
32 elements
After Lanthanum (La) fourteen elements are shown separately at the bottom
Periodic table Periods
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
Period 2 and 3 : Short periods
Each contains 8 elements 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Period 4 and 5 : Long periods
Each contains 18 elements

34. Periodic table Alkali metals (Group 1)
1 electron in outermost orbit
Good reducing agents
React with water and release Hydrogen 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

35. Periodic table Alkaline earth metals (Group 2)
Two electrons in outermost orbit
Fairly good reducing agents
They release CO2 when their carbonate compounds are heated 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

36. Periodic table Transition elements and other metals
Metallic properties reduce from left to right 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

37. Periodic table Non-metals and metalloids18 1
Metalloids 2 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 3 4 5 6 7

38. Periodic table Halogens (Group 17)
7 electrons in the outermost orbit
Good oxidising agents
Periodic table Halogens (Group 17) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

39. Periodic table Inert gases (group 18)
Outer orbits are fully filled with electrons
Chemically inactive
Periodic table Inert gases (group 18) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

40. Periodic table Classification according to external sub-orbit of atom
P Blockû
D Block
f Block
S Blockû
1 H
2 He
3 Li
4 Be
5 B
6 C
7 N
8 O
9 F
10 Ne
11 Na
12 Mg
13 Al
14 Si
15 P
16 S
17 Cl
18 Ar
19 K
20 Ca
21 Sc
22 Ti
23 V
24 Cr
25 Mn
26 Fe
27 Co
28 Ni
29 Cu
30 Zn
31 Ga
32 Ge
33 As
34 Se
35 Br
36 Kr
37 Rb
38 Sr
39 Y
40 Zr
41 Nb
42 Mo
43 Tc
44 Ru
45 Rh
46 Pd
47 Ag
48 Cd
49 In
50 Sn
51 Sb
52 Te
53 I
54 Xe
55 Cs
56 Ba
57- 71
72 Hf
73 Ta
74 W
75 Re
76 Os
77 Ir
78 Pt
79 Au
80 Hg
81 Tl
82 Pb
83 Bi
84 Po
85 At
86 Rn
87 Fr
88 Ra
104 Rf
105 Db
106 Sg
107 Bh
108 Hs
109 Mt
110 Uun
111 Uuu
112 Uub
113 Uut
114 Uuq
115 Uup
116 Uuh
117 Uus
118 Uuo
57 La
58 Ce
59 Pr
60 Nd
61 Pm
62 Sm
63 Eu
64 Gd
65 Tb 66 Dy
67 Ho
68 Er
69 Tm
70 Yb
71 Lu
89 Ac
90 Th
91 Pa
92 U
93 Np
94 Pu
95 Am
96 Cm
97 Bk
98 Cf
99 Es
100 Fm
101 Md
102 No
103 Lr 1 2 3 4 5 6 7

41. Periodic table Electron configuration4s 3p 3s 2p 2s
Energy 1s
S block
d block
p block 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
f block

42. 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)

43. The End