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9th Class Science Atoms and Molecules Atoms

Atoms

Category : 9th Class

*        Atoms

 

According to modern atomic theory, an atom is the smallest particle of elements. It takes parts in the chemical reaction and maintains its identity throughout all physical and chemical changes. Since the atoms of elements are quite reactive, they do not exist in Free State except for noble gases. All the atoms consist of subatomic particles called electron, proton and neutron. The number of electrons and protons in an atom is always found to be the same. The electron revolve around the nucleus in a fixed orbit and the proton and the neutron are present in the nucleus of an atom. The atoms are very smaller is size and cannot be seen by the naked eyes. The size of an atom is measured by its radius called the atomic radius. The atomic radius of smallest atom Hydrogen is 0.37 x 10-10 m or 0.037 nm. 1 nm = 10-9 m.

The atoms are normally denoted by symbols. It was Daltons who introduced the use of symbol to denotes the atoms of different elements. Dalton's symbol for some of the elements are given below:

 

Element Symbol
Hydrogen
Carbon
Oxygen
Nitrogen
Sulphur
Phosphorus
Lead
Iron
Copper
Zinc
Silver
Mercury

 

 

*        Modern Symbols and Atomic Numbers for Some of the Elements  

Elements Symbols Atomic Nos. Mass Nos.

Hydrogen

Helium

Lithium

Beryllium

Boron

Carbon

Nitrogen

Oxygen

Fluorine

Neon

Sodium

Magnesium

Aluminium

Silicon

Phosphorous

Sulphur

Chlorine

Argon

Potassium (Kalium)

Calcium

Iron (ferrum)

Copper(Cuprum)

Silver (Argentum)

Lead (Plumbum)

Mercury (Hydragyrum)

H

He

Li

Be

B

C

N

0

F

Ne

Na

Mg

Al

Si

P

S

Cl

Ar

K

Ca

Fe

Cu

Ag

Pb

Hg

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

26

29

47

82

80

1

4

7

9

11

12

14

16

19

20

23

24

27

28

31

32

35

38

39

40

56

64

108

207

201

 

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