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The Fundamental Unit of Life
State the observations made, while conducting a discharge experiment, which showed that
(i) Cathode rays travel in straight lines.
(ii) Cathode rays are made up of material particles having mass and kinetic energy.
(iii) Cathode rays are negatively charged.
(i) Cathode rays cast shadow of the objects placed in their path. This observation shows that cathode rays travel in straight lines.
(ii) It was observed that cathode rays could rotate the paddle of light wheel. This suggested that cathode rays possess mass and hence kinetic energy.
(iii) The cathode rays were deflected towards positive plate of the electric field applied in their path. This shows that cathode rays are negatively charged particles because only opposite charge attract each other.
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Describe Bohr's model of the atom ?
Compare all the proposed models of an atom given in this chapter.
Summarize the rules for writing of distribution of electrons in various shells for the first eighteen elements.
Define valency by taking examples of silicon and oxygen.
Explain with examples, (i) Atomic number, (ii) Mass number, (iii) Isotopes, and (iv) Isobars. Give any two uses of isotopes also.
Na+ has completely filled K and L-shells. Explain.
If Z = 3, what would be the valency of the element? Also, name the element.
Composition of the nuclei of two atomic species X and Y are given as under
X Y
Protons = 6 6
Neutrons= 6 6
Give the mass numbers of X and Y. What is the relation between the two species?
For the following statements, write T for True and F for False.
(a) J.J. Thomson proposed that the nucleus of an atom contains only nucleons.
(b) A neutron is formed by an electron and a proton combining together. Therefore, it is neutral.
(c) The mass of an electron is about 1/2000 times that of proton.
(d) An isotope of iodine is used for making tincture iodine, which is used as a medicine.
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