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?
Describe Bohr’s model of the atom.
Draw a sketch of Bohr’s model of an atom with three shells.
Write the electronic configuration of any one pair of isotopes and isobars.
Na+ has completely filled K and L shells. Explain.
How will you find the valency of chlorine, sulphur and magnesium?
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 are polyatomic ions? Give examples.
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 would happen if the plasma membrane ruptures or breaks down?
Identify the solutions among the following mixtures.
(a) Soil
(b) Sea water
(c) Air
(d) Coal
(e) Soda water.
Why will a sheet of paper fall slower than one that is crumpled into a ball?
Does sound follow the same laws of reflection as light does? Explain.
Hydrogen and oxygen combine in the ratio of 1:8 by mass to form water. What mass of oxygen gas would be required to react completely with 3 g of hydrogen gas?
Name the technique to separate
(i) butter from curd,
(ii) salt from sea-water,
(iii) camphor from salt.
Does the transfer of energy take place when you push a huge rock with all your might and fail to move it? Where is the energy you spend going?
What do you mean by buoyancy?