chemistry holiday homework

PODAR INTERNATIONAL SCHOOL

CLASS :9                         HOLIDAY HOMEWORK                 SUB:CHEMISTRY

I.                   Learn the chapter “MATTER IN OUR SURROUNDINGS” and complete your written work.

II.               LET’S RECALL CLASS 7 PORTION

Symbols of elements and radicals

A.   The symbol represents the abbreviated form of the element.

It is usually the capitalized first letter of the elements. E.g.

ELEMENT	SYMBOL
Hydrogen	H
Oxygen	O
Carbon	C
Boron	B
Sulphur	S
Iodine	I
Nitrogen	N
Phosphorus	P

B.   When there are two or more elements begin with the same letter, their symbols take two letters. The first letter is capitalized while the second in small letter. E.g.

element	symbol	element	symbol
Calcium	Ca	Neon	Ne
Helium	He	Argon	Ar
Lithium	Li	Barium	Ba
Beryllium	Be	Cobalt	Co
Aluminium	Al	Nickel	Ni
Titanium	Ti	Germanium	Ge
Gallium	Ga	Selenium	Se

  

    C  . THE SYMBOLS OF SOME ELEMENTS ARE DERIVED FROM THEIR Latin, Greek or German names.

element	symbol	element	symbol
Potassium	K	Sodium	Na
Silver	Ag	Magnesium	Mg
Gold	Au	Lead	Pb
Mercury	Hg
Platinum	Pt
Zinc	Zn
Copper	Cu

VALENCY:

When the elements combine to form compounds, they have different capacities to combine with atoms of other elements.

Valency is the ability or the combining capacity of an atom to combine with atoms of different elements.

For e.g. in water, one oxygen atom combines with teo hydrogen atoms to form one water molecule. So, the valency of oxygen is 2.

H                H                                            H         N         H

         O                                                                   H

 water                                           In ammonia,      Nitrogen valency is 3

Atomic Number	element	symbol	valency
1	Hydrogen	H	1
2	Helium	He	0
3	Lithium	Li	1
4	Beryllium	Be	2
5	Boron	B	3
6	Carbon	C	4
7	Nitrogen	N	3
8	Oxygen	O	2
9	Fluorine	F	1
10	Neon	Ne	0
11	Sodium	Na	1
12	Magnesium	Mg	2
13	Aluminium	Al	3
14	Silicon	Si	4
15	Phosphorus	P	3,5
16	Sulphur	S	2
17	Chlorine	Cl	1
18	Argon	Ar	0

Name of the radical	symbol	valency
Hydroxide	OH	1
Nitrate	NO3	1
Sulphate	SO4	2
Carbonate	CO3	2
Phosphate	PO4	3
Fluoride	F	1
Bromide	Br	1
Oxide	O	2

Sulphide                       S                           2

Nitride                          N                           3

How to write chemical formula:

-         First step-

1.Write down the symbol of the element

Second step

2.Write the valency of the element and radical as superscripts

Third step

3. interchange their valencies

If the valencies are divided by common number, simplify the numbers in the subscript.

4. if 2 or more units of a radical are involved, then the radical is enclosed within the brackets and the no. is written as subscript outside the bracket.

e.g. Magnesium Sulphate

   Mg                          SO₄

            Write their valencies

            Mg²                        SO₄²  (interchange their valencies)

              

                      Mg₂                ( SO₄)₂

if 2 or more units of a radical are involved, then the radical is enclosed within the brackets and the no. is written as subscript outside the bracket.

HOME WORK:

WRITE THE CHEMICAL FORMULAE OF THE FOLLOWING COMPOUNDS (write in assignment sheet & submit it)

1.    Calcium oxide

2.    Sodium Oxide

3.    Zinc Hydroxide

4.    Calcium Chloride

5.    Magnesium Chloride

6.    Barium Chloride

7.    Sodium Sulphide

8.    Calcium Carbonate

9.    Calcium Nitrate

10.           Copper Nitrate

11.           Copper sulphate

12.           Hydrogen Fluoride

13.           Aluminium Nitride

14.           Aluminium Sulphide

15.           Potassium Hydroxide

16.           Sodium Hydroxide

17.           Magnesium Sulphate

18.           Magnesium Carbonate

19.           Zinc Chloride

20.           Copper Carbonate