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• Matter is classified into solids, liquids and gases.
• Matter can also be classified into elements, compounds and mixtures based on composition
Fe, Ag, Au, Cu,
• Iron element is made of iron atoms. Silver element is made of silver atoms.
Elements are the pure substances
containing only one kind atoms, which
cannot be decomposed by any physical or
chemical process.
All matter is composed of small
particles called “atoms”. Atom is
made of smaller particles (sub atomic
particles) are called the fundamental
particles.
The number of subatomic particles known is
very large. For us, the three most important
are the proton, neutron and electron. It is a
fascinating story that these. Fundamental
particles go to make the internal structure of
the atom.
Chemists have discovered 118
elements so far. Among these
elements, 92 are normal elements
and remaining are synthetic
elements.
1. An element is a pure substance, made up of only one kind of atoms
2. An atom is smallest particle of an
element and it possesses properties of that element
3. Elements may occur in the free
state in nature or found in the form of their compounds.
Eg:- Iron → FeS, Fe2O3, Fe3O4,
Ag, Au → Native form
Cu → CuFeS2
�Some elements (like radioactive elements) can be prepared artificially by nuclear reaction.
eg: 88Ra226
→ 86Rn222 + 2He
4
Radium Radon
The properties of different elements are
different. This is because, the arrangement of
electrons (electronic configuration) in atoms are
different.
Li F He
Na Cl Ne
K Br Kr
Need for classification of elements
During 17th century, only few elements were
known. Later on many elements were
discovered in nature, the number of elements in
the list of known elements went on increasing.
It was thought that elements must be properly
classified in order to make a systematic study
of elements, otherwise it becomes impossible
to understand the properties of elements.
Advantages of classification of elements.
i) To study the elements in a systematic
manner.
ii) To correlate the properties of
elements. (Eg: H20, HNO3, HCl]
iii) To know the type of different
elements, compounds from that
different elements can form.
Historical background of classification of
elements :
Earlier, an attempt was made to classify the
elements into metals and non-metals.
Metals
An element is a metal if it has the following properties
1. It is lustrous i.e., it has shining surface.
2. It is a good conductor of heat and electricity.
3. It is ductile i.e.,it can be drawn into wires.
4. It is malleable i.e., it can be beaten into thin sheets.
5. It is solid at room temperature.
6. It has a tendency to lose one or more electrons.
Exceptions: Mercury and Gallium are liquids at room temperature. Zinc is not malleable and ductile.
Sl N
Name in English Name in other language
Symbol
1 Lithium - Li
2 Sodium Natrium (latin) Na
3 Magnesium Mg
4 Aluminium Al
5 Potassium Kalium ( Latin) K
6 Calcium Ca
7 Vanadium V
8 Chromium Cr
9 Manganese Mn
10 Iron Errum ( Latin) Fe
11 Cobalt Co
12 Nickel Ni
13 Copper Cuprum (Latin) Cu
14 Zinc Zn
15 Gallium Ga
16 Silver Argentums (Latin) Ag
17 Tin Stannum (latin) Sn
18 Barium - Ba
19 Platinum - Pt
20 Gold Aurum (Latin) Au
21 Mercury Hydrargyrum (Latin) Hg
22 Lead Plambun (latin) Ph
23 Radium - Rq
24 Uranium Wolram (German) U
25 Tungsten - W
26 Thorium - Th
Johann Wolfgang Döbereiner
(1780-1849)
Döbereiner grouped elements to show that atomic weights of a middle element were an average of two similar elements.
Examples of Döbereiner’ Triads:
“…the atomic weight of bromine might be the
arithmetical mean of the atomic weights of
chlorine and iodine. This mean is
(35.470+126.470)/2 = 80.470
This number is not much greater than that found
by Berzelius (78.383)”
Using modern values: Cl = 35.45
Br = 79.90
I = 126.90
“In the alkali group, soda stands in the middle
Using modern values:
Li = 6.94
Na = 22.99
K = 39.10
Atm. of Li + Atm.of KAtm. of Na= ----------------------------------
2
Periodic Law� The properties of elements are a periodic
function of their atomic number
P = F(z)
Periodic Law� When elements are
arranged in order of
atomic number, similar
properties recur
periodically.Li
NaK
Atomic radii vs. Z
Atomic number
First Io
niza
tion
En
ergy
Chemical
and
Physical
properties
Type of
Bonding
and
structure
Atomic
properties
Atomic number
H
HeNe
Ar
Li Na K
N
Be
B
C O
F
Mg
P
Al
Si SCl
Ca
Atomic number
Firs
t I.E.
Variations:
1. Across a period
2. Down the group
H
He
Li
Na
Ne
Ar
K
Be
Mg
Ca
H
37
He
54
Li
156
Be
105
B
91
C
77
N
71
O
60
F
67
Ne
80
Na
186
Mg
160
Al
143
Si
117
P
111
S
104
Cl
99
Ar
96
K
231
Ca
197
Sc
161
Ti
154
V
131
Cr
125
Mn
118
Fe
125
Co
125
Ni
124
Cu
128
Zn
133
Ga
123
Ge
122
As
116
Se
115
Br
114
Kr
99
Rb
243
Sr
215
Y
180
Zr
161
Nb
147
Mo
136
Tc
135
Ru
132
Rh
132
Pd
138
Ag
144
Cd
149
In
151
Sn
140
Sb
145
Te
139
I
138
Xe
109
Cs
265
Ba
210
Hf
154
Ta
143
W
137
Re
138
Os
134
Ir
136
Pt
139
Au
144
Hg
147
Tl
189
Pb
175
Bi
155
Po
167
At
145
Rn
La
187
Ce
183
Pr
182
Nd
181
Pm
181
Sm
180
Eu
199
Gd
179
Tb
176
Dy
175
Ho
174
Er
173
Tm
173
Yb
194
Lu
172
Atomic Radius (pm) 1pm=1x10-12m
H
He Ne Ar
F
Cl
LiNa
K
Ca
Ele
ctr
onegativity
Atomic number
H
2.1
Li
1.0
Be
1.5
Na
0.9
Mg
1.2
Al
1.0
K
0.8
B
2.0
C
2.5
N
3.0
O
3.5
F
4.0
Al
1.5
Si
1.8
P
2.1
S
2.5
Cl
3.0
Ne
-
Ar
-
He
-
Increase in electronegativity
Decrease
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