1 Atomic Structure and Periodic Table. 2 What are we going to learn ? Part 1: Atomic structure...
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Transcript of 1 Atomic Structure and Periodic Table. 2 What are we going to learn ? Part 1: Atomic structure...
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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 1766 - 1844
5
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?
6
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 ?
7
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?
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 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)
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)
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 = ?
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
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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
15
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
18
Inside the atom Electron configuration of elements - Helium
1s 2s 2p 3s
He
2
4
1s2
19
Inside the atom Electron configuration of elements - Lithium
Li3
7
1s 2s 2p 3s
1s2, 2s1
20
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
22
Inside the atom Electron configuration of elements - Carbon
C6
12
1s 2s 2p 3s
66
1s2, 2s2, 2p2
23
Inside the atom Electron configuration of elements- Nitrogen
N7
14
1s 2s 2p 3s
77
1s2, 2s2, 2p3
24
Inside the atom Electron configuration of elements- Oxygen
O8
16
1s 2s 2p 3s
88
1s2, 2s2, 2p4
25
Inside the atom Electron configuration of elements - Fluorine
F9
19
1s 2s 2p 3s
10
9
1s2, 2s2, 2p5
26
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
19
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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
35
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
37
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
38
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
40
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
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)
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The End