Summarise the rules for writing of distribution of electrons in various shells for the first eighteen elements.
The standards for composing of appropriation of electrons in different shells for the initial eighteen components are:
(I) The most extreme number of electrons present in a shell is given by the formula 2 n2
∵ n = orbit number i.e., 1, 2, 3
∵ Maximum number of electrons in various shells are:
K shell n = 1 2n2 => 2(1)2 = 2
L shell n = 2 2n2 => 2(2)2 = 8
M shell n = 3 2n2 => 2(3)2 = 18
N shell n = 4 2n2 => 2(4)2 = 32
(ii) The most extreme number of electrons that can be obliged in the furthest orbit is 8.
(iii) Electrons are not obliged in a given shell except if the internal shells are filled.
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.
Explain with examples (i) Atomic number, (ii) Mass number, (iii) Isotopes and iv) Isobars. Give any two uses of isotopes.
Define valency by taking examples of silicon and oxygen.
Na+ has completely filled K and L shells. Explain.
Write the electronic configuration of any one pair of isotopes and isobars.
Draw a sketch of Bohr’s model of an atom with three shells.
Describe Bohr’s model of the atom.
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?
You find your mass to be 42 kg on a weighing machine. Is your mass more or less than 42 kg?
The volume of 50 g of a substance is 20 cm3. If the density of water is 1 g cm-3, will the substance float or sink?
On what bases are plants and animals put into different categories?
A racing car has a uniform acceleration of 4 m s-2. What distance will it cover in 10 s after start?
Explain the basis for grouping organisms into five kingdoms.
What is the nature of the distance-time graphs for uniform and non-uniform motion of an object?
A train is travelling at a speed of 90 km h-1. Brakes are applied so as to produce a uniform acceleration of – 0.5 m s-2. Find how far the train will go before it is brought to rest.
What does a neuron look like?
Gravitational force acts on all objects in proportion to their masses. Why then, a heavy object does not fall faster than a light object?
What are the differences between the mass of an object and its weight?