• 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