CLASS-9
ATOMS AND MOLECULES
STRUCTURE OF AN ATOM

1. If an element M has atomic mass 27 and atomic number 13.How many electrons and neutrons does it contain? What valency should be shown by M?

2. WRITE THE ELECTRONIC CONFIGURATION  OF AN ATOM WITH ATOMIC NUMBER 6.

3.What are the limitations of Rutherford's Model of an atom?

4.Calculate the number of aluminium atoms present in 0.05g of aluminium oxide(Al2O3).(Al=27,O=16)

5.What are polyatomic ions? Give examples?

6.Write the chemical formulae of the following:
(a)        Magnesium chloride
(b)        Calcium oxide
(c)        Copper nitrate
(d)       Aluminium chloride
(e)        Calcium carbonate

7.What is the mass of−−
(a) 1 mole of nitrogen atoms?
(b) 4 moles of aluminium atoms (Atomic mass of aluminium = 27)?
(c) 10 moles of sodium sulphite (Na₂SO₃)?

 8.Describe Bohr’s model of the atom.

 9.Compare all the proposed models of an atom given in this chapter.

Thomson’s model	Rutherford’s model	Bohr’s model
An atom consists of a positively charged sphere with electrons embedded in it.	An atom consists of a positively charged particles concentrated at the centre known as the nucleus. The size of the nucleus is very small as compared to the size of the atom. The electrons revolve around the nucleus in well-defined orbits.	There are only certain orbits known as discrete orbits inside the atom in which electrons revolve around the nucleus. Electrons do not radiate energy while revolving.

10.Write the distribution of electrons in carbon and sodium atoms?

The total number of electrons in a carbon atom is 6. The distribution of electrons in carbon atom is given by:
First orbit or K-shell = 2 electrons
Second orbit or L-shell = 4 electrons
Or, we can write the distribution of electrons in a carbon atom as 2, 4.
The total number of electrons in a sodium atom is 11. The distribution of electrons in sodium atom is given by:
First orbit or K-shell = 2 electrons
Second orbit or L-shell = 8 electrons
Third orbit or M-shell = 1 electron

11.If K and L shells of an atom are full, then what would be the total number of electrons in the atom?

 The maximum number of electrons that can occupy K and L-shells of an atom are 2 and 8 respectively. Therefore, if K and L-shells of an atom are full, then the total number of electrons in the atom would be 10 

12 What do you think would be the observation if the α-particle scattering experiment is carried out using a foil of a metal other than gold?

If the α-scattering experiment is carried out using a foil of a metal rather than gold, there would be no change in the observation. In the α-scattering experiment, a gold foil was taken because gold is malleable and a thin foil of gold can be easily made. It is difficult to make such foils from other meta

12.Complete the following table

.

13.Write the electronic configuration of any one pair of isotopes and isobars.

14.How will you find the valency of chlorine, sulphur and magnesium?

If the number of electrons in the outermost shell of the atom of an element is less than or equal to 4, then the valency of the element is equal to the number of electrons in the outermost shell. On the other hand, if the number of electrons in the outermost shell of the atom of an element is greater than 4, then the valency of that element is determined by subtracting the number of electrons in the outermost shell from 8.

The distribution of electrons in chlorine, sulphur, and magnesium atoms are 2, 8, 7;    2, 8, 6 and        2, 8, 2 respectively.

Therefore, the number of electrons in the outer most shell of chlorine, sulphur, and magnesium atoms are 7, 6, and 2 respectively.

Thus, the valency of chlorine = 8 −7 = 1

The valency of sulphur = 8 − 6 = 2

The valency of magnesium = 2

15.If number of electrons in an atom is 8 and number of protons is also 8, then (i) what is the atomic number of the atom and (ii) what is the charge on the atom?

(i) The atomic number is equal to the number of protons. Therefore, the atomic number of the atom is 8.

(ii) Since the number of both electrons and protons is equal, therefore, the charge on the atom is 0.

16.Composition of the nuclei of two atomic species X and Y are given as under

                 X                Y

Protons =   6              6

Neutrons = 6               8

Give the mass numbers of X and Y. What is the relation between the two species?Mass number of X = Number of protons + Number of neutrons

= 6 + 6

= 12

Mass number of Y = Number of protons + Number of neutrons

= 6 + 8

= 14

These two atomic species X and Y have the same atomic number, but different mass numbers. Hence, they are isotopes.

CLASS -VII 

LESSON -WATER

Q1: Name the available water resource on earth.

Q2: Water that is fit for human consumption is called_________________.

Q3: What per cent of total water on the earth is actually available for our use

Q4: As a solid, water exists as icecaps at the poles. True/ False.

Q5: People obtain ---------through tube wells and hand pumps.

Q6: Three forms of water are solid, liquid and ---------.

Q7: The water bearing layer of the earth is ----------.

Q8: The process of water seepage into the ground is called ---------.

Q9: The process of changing of water into its vapour is called---------.

Q10: The process of changing water vapour into water is called ---------

Q11: No rainfall for a year or more may lead to ---------- in that region.

Q12: Excessive rains may cause -----------.

Q13: What are main sources of water?

1. Rainwater
2. Glaciers, ice
3. River water
4. sea and Ocean water
5. All of the above

Q14: Why ice floats on water?

Q15: Name the gaseous form of water around us.

Q16: Sometimes, ground water accumulates between layers of hard rock. This is known as an aquifer. True/False

Q17: Plants use ground water and release it in the form of water vapour during transpiration. True/False

Q18: Clouds then release the water through ___________________.

Q19: Is increasing population is the reason for depletion of water table?

Q20: What is water management?

Q21: What do you mean by water harvesting?

Q22: State the advantage of water harvesting?

Q23: What is drip irrigation?

Q24: State the use of water in plants.

Q25: Which day is celebrated as World’s Water Day?

Q26: Name the process responsible for maintenance of water on earth.

Q27 write differences between hard and soft water?

Q28: Define infiltration.

Q29: What is aquifer?

Q30: Which of the following is the reason for depletion of water table?

1. Increasing population
2. Increasing industries
3. Deforestation
4. All of the above

Q31: How water in an aquifer can be pumped out?

Q32: How does underground water gets replenished?

Q33: State factors affecting water table

.Q34: You have been asked to maintain a garden. How will you minimise the use of water?

Q35: There are ten tubewells in a lane of fifty houses. What could be the long term impact on the water table?

Q36: Explain how we can recharge ground water?

Q37: Show groundwater and water table via a sketch.

Q38: Can we keep on drawing water from underground, how it will affect the water table?

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q39 Explain the factors responsible for depletion of water table.

worksheet on mole concept

class-9

Mole is defined as the amount of substance that contains as many specifi ed elementary particles as the number of atoms in 12g of carbon-12 isotope. 

One mole is also defined as the amount of substance which contains Avogadro number (6.023 x 1023) of 
particles
(a). Calculate the number of moles in  (i) 81g of aluminium ii) 4.6g sodium  (iii) 5.1g of Ammonia  (iv) 90g of water  (v) 2g of NaOH 

Solution: (i) Number of moles of aluminum = given mass of aluminium / atomic mass of aluminium = 81/27 = 3 moles of aluminum [Rest Question do yourself

(b) Calculate the mass of 0.5 mole of iron

Solution: mass = atomic mass x number of moles = 55.9 x 0.5 = 27.95 g

Problem: Calculate the number. of molecules in 11g of CO₂

Solution: gram molecular mass of CO₂ = 44g

Number of molecules = (6.023 x 10²³ x 11) / 44 = 1.51 x 10²³ molecules

Problem: Calculate the mass of 18.069 x 10² molecules of SO₂

Problem: Calculate the number of aluminum ions present in 0.051 g of aluminum oxide. (Hint: The mass of an ion is the same as that of an atom of the same element. Atomic mass of Al=27 u)

Solution: Mass of the 1 mole of Al₂ O₃  = 2x27 + 3x16 = 102gm

The number of ions present in 102 gm of aluminum oxide  = 6.023 x 10²³ ion

The number of ions present in 0.051g of aluminum oxide= (6.023 x 10²³ ion x 0.051g)/ 102 gm 

=  6.023 x 10²³ ion x0.0005 = 3.0115 x 10²⁰ ions

In Al₂ O₃, Aluminium and oxygen are in ratio 2:3

So, The number of aluminum ions present(Al³⁺) in 0.051g of aluminum oxide = 2 x 3.0115 x 10²⁰ ions =6.023 x 10²⁰ ion³ 

Problem:  Calculate the number moles for a substance containing 3.0115 x 10²³ molecules in it.

Volume occupied by one mole of any gas at STP is called molar volume. Its value is 22.4 litres 22.4 litres of any gas contains 6.023 x 1023 molecules.

Problem: Calculate the volume occupied at STP by :- (a) 64 gram of oxygen gas (b) 6.02 x10²² molecules of CH₄ 

Solution: (a) One mole of a gas occupies 22.4 L volume at STP

Now, number of moles in 64 g oxygen gas = 64/32 = 2

Therefore, volume occupied by 2 moles(64 g) of oxygen gas = 2 x 22.4 L = 44.8 L

(b) 1 mole = 6.02 x 10²³ molecules

Therefore, 1 mole (6.02 x 10²³ molecules) of CH₄ gas occupies 22.4 L volume at STP.

*****

  CLASS-VII                                                            TOPIC -LIGHT              SUB:-LIGHT
Objective type Questions:
1. Out of convex mirror and concave mirror, whose focus is situated behind themirror?


2. A ray of light falls on a mirror normally. What are the values of angle of incidence and the angle of reflection

3 Which spherical mirror is called a divergent mirr

4 Name the type of mirror that always forms a virtual image for a real object?

5. Which of the two is a diverging lens? Convex lens (or) Concave lens.

Short types Questions
Q1. What do you mean by reflection of light?
Q2. How does a path of light can be changed?
Q3. What are the laws of reflection?

Q4. What is the nature of image formed in a plane mirror
Q5. Difference between real & virtual image

Q6. What type of mirror – the inner surfact of the Spoon acts as and the outer surface of the spoon acts as ?

Q7. Which concave mirror called a converging mirror and a convex mirror called a diverging mirror
Q8. What is the nature of image formed in a convex mirror?

Q9. What is the nature of image formed in a concave mirror?

Q10. What are the uses of concave mirror?

11. What are the uses of Convex mirror?

Q12. What are uses of Plane Mirror?

Q13. What is a lens?.
Q15. Why a convex lens is called a converging lens and a concave lens a diverging lens?

Q16. What is the nature of image formed in a concave lens?

Q17. What is the nature of image formed in a convex lens?

Q18. What are the uses of lens
Q19. How is the rainbow formed?
Q20. Where else you can see seven colours of sunlight?

Q 21. State the characteristics of the image formed by a plane mirror.

Q22. Fill in the blanks

a. An image that cannot be obtained on a screen is called --------

b. Image formed by a convex ------------- is always virtual and smaller in size.
c. An image formed by a ------------- mirror is always of the same size as that of the object.
d. An image which can be obtained on a screen is called a ----------- image.
e. An image formed by a concave ------------ cannot be obtained on a screen.

PRESSURE

class 8 Air pressure