Explain with examples (i) Atomic number, (ii) Mass number, (iii) Isotopes and iv) Isobars. Give any two uses of isotopes.
(I) Atomic number: The atomic number of a component is equivalent to the quantity of protons in the nucleus of its molecule.
e.g., Oxygen has 6 protons thus atomic no. = 6.
(ii) Mass number: The mass number of a molecule is equivalent to the quantity of protons and neutrons in its nucleus.
Nucleons = number of protons + number of neutrons
Example: Protons + Neutrons = Nucleus = Mass number = 6 + 6 = 12
(iii) Isotopes: Isotopes are molecules of a similar component which have different mass numbers however same atomic number.
(iv) Isobars: Isobars are molecules having similar mass number however different atomic numbers.
Both calcium and argon have a similar mass number yet unique atomic number.
Two uses of isotopes are:
(I) An isotope of iodine is utilized in the treatment of goiter.
(ii) An isotope of uranium is utilized as a fuel in atomic reactors.
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?
With the help of Table 4.1, find out the mass number of oxygen and sulphur atom.
For the symbol H,D and T tabulate three sub-atomic particles found in each of them.
Define valency by taking examples of silicon and oxygen.
The average atomic mass of a sample of an element X is 16.2 u. What are the percentages of isotopes 168 X and 188 X in the sample?
Draw a sketch of Bohr’s model of an atom with three shells.
Describe Bohr’s model of the atom.
Na+ has completely filled K and L shells. Explain.
Write the electronic configuration of any one pair of isotopes and isobars.
Compare all the proposed models of an atom given in this chapter.
Which of the following has more inertia: (a) a rubber ball and a stone of the same size? (b) a bicycle and a train? (c) a five-rupees coin and a one-rupee coin?
State the universal law of gravitation.
Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, cold-drink, smell of perfume.
A force of 7 N acts on an object. The displacement is, say 8 m, in the direction of the force (Fig. 11.3). Let us take it that the force acts on the object through the displacement. What is the work done in this case?
What is meant by a pure substance?
How does the sound produced by a vibrating object in a medium reach your ear?
In a reaction, 5.3 g of sodium carbonate reacted with 6 g of ethanoic acid. The products were 2.2 g of carbon dioxide, 0.9 g water and 8.2 g of sodium observations are in agreement with the law of conservation of mass.
sodium carbonate + ethanoic acid → sodium ethanoate + carbon dioxide + water
State any two conditions essential for good health.
How is our atmosphere different from the atmospheres on Venus and Mars?
Who discovered cells, and how?
What type of clothes should we wear in summer?
Give reasons
(a) A gas fills completely the vessel in which it is kept.
(b) A gas exerts pressure on the walls of the container.
(c) A wooden table should be called a solid.
(d) We can easily move our hand in air but to do the same through a solid block of wood we need a karate expert.
How does the water kept in an earthen pot (matka) become cool during summer?
What are polyatomic ions? Give examples.
What does a neuron look like?
When will you say a body is in
(i) uniform acceleration? (ii) non-uniform acceleration?
Identify the solutions among the following mixtures.
(a) Soil
(b) Sea water
(c) Air
(d) Coal
(e) Soda water.
Why is ice at 273 K more effective in cooling than water at the same temperature?
Under which of the following conditions are you most likely to fall sick?
(a) when you are taking examinations.
(b) when you have travelled by bus and train for two days.
(c) when your friend is suffering from measles.
Why?
Which of the following materials fall in the category of a “pure substance”?
(a) Ice
(b) Milk
(c) Iron
(d) Hydrochloric acid
(e) Calcium oxide
(f) Mercury
(g) Brick
(h) Wood
(i) Air.