Class 7th Science // Chapter 1

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Chapter 1 -The language of chemistry 
• How are atom , molecule and chemical change represented ?
Ans:- An atom is represented by a symbol , a molecule by a formula and a chemical change by a chemical equation . 

•  What is a symbol of an element ?
Ans:- A symbol is an abbreviation of the name of an element .
For example:-
Hydrogen - H  ,  Oxygen - O
Helium - He   ,  Magnesium - Mg 
Sodium - Na  , Potassium - K

• The symbol of elements have been derived in three different ways - 
1. By the first letter (in capital) of the English name of an element . 
For example:- 
Hydrogen - H  ,  Oxygen - O
Sulphur - S  ,  Boron - B
Carbon - C  ,  Nitrogen - N

2. By first letter along with one more letter of the English name of an element . 
For Example:-
Helium - He   ,  Magnesium - Mg 
Aluminium - Al  ,  Neon - Ne 
Nickel - Ni , Manganese - Mn 
Calcium - Ca  ,  Chlorine - Cl 
Zinc - Zn 
3. By one or two letters of the Latin name of an element. 
For Example :
Elements Name Latin Name Symbol
1. Sodium Natrium Na
2. Potassium Kalium K
3. Iron Ferrum Fe
4. Copper Cuprum Cu
5. Silver Argentum Ag
6. Gold Aurum Au
7. Tin Stannum Sn
8. Lead Plumbum Pb
9. Mercury Hydragynum Hg
10. Antimony Stibium Sb
11. Tungsten Wolfram
W

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• What is molecule ? 
Ans:- A molecule is the smallest part of an element or a compound that can exist independently . 
 Molecule is represented by formula . 

Note :- 
1. The formula of a molecule gives the number of atoms of the same or different elements present in the molecule.
2. When an atom of an element combine with another atoms of the same element , a molecule of the element is formed . 
For example :- 2- atoms of Hydrogen combine to form a molecule of Hydrogen . 
H + H ⟶ H2 
3. Hydrogen , Nitrogen , Oxygen , Fluorine , Chlorine , Bromine , and Iodine contain two atoms of the element . So they are represented by 
Hydrogen ( H2 )
Nitrogen  (N2 )
Oxygen ( O2 )
Fluorine ( F2 )
Chlorine ( Cl2 )
Bromine ( Br2 )
Iodine ( I 2)

• What is monoatomic ? 
Ans:- Such molecule of an element which contains only one atom of the element is called monoatomic . 
Example : Helium ( He ) , Neon ( Ne ) , Argon ( Ar ) , Krypton ( Kr ) , Xenon ( Xe ) , Redon ( Rn ) 
Note : Monoatomic gases are called noble gases / inert gases .

• What is diatomic ?
Ans:- Such molecule of an element which contains two atom of the element is called diatomic .
Example: H2 , N2 , O2 , Cl2 , F2 , I2 

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• What is valency ? 
Ans:- The capacity of an element to combine with other elements is known as its valency.

# The  symbol and valency of some Radical 
Radicals Symbol Valency
1. Hydrogen H 1
2. Sodium Na 1
3. Potassium K 1
4. Ammonium Al 1
5. Magnesium Mg 2
6. Calcium Ca 2
7. Zinc Zn 2
8. Barium Ba 2
9. Boron B 3
10 Bromide Br 1
11. Bismuth Bi 3
12. Aluminium Al 3
13. Chromium Cr3
14. Cuprous Cu 1
15. Cupric Cu 2
16. Ferrous Fe 2
17. Feric Fe 3
18. Stannous Sn 2
19. Stannic Sn 4
20. Plumbous Pb 2
21. Plumbic Pb 4
22. Hydride H 1
23. Chloride Cl 1
24. Iodide I 1
25. Fluoride F 1
26. Hydroxide OH 1
27. Nitrite NO2 1
28. Nitrate NO3 1
29. Bicarbonate HCO31
30. Carbonate CO3 2
31. Bisulphate HSO4 1
32. Bisulphide HS 1
33. Chlorate ClO3 1
34. Permangnate MNO4 1
35. Sulphate SO4 2
36. Sulphite SO3 2
37. Sulphide S 2
38. Oxide O 2
39. Peroxide O2 2
40. Chromate CrO4 2
41. Bicarbonate HCO31
42. Silicate SiO3 2
43. Zincate ZnO2 2
44. Nitride N 3
45 . Carbide C 4

The End 
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