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The Fundamental Unit of Life
Define the terms:
(i) atomic number
(ii) mass number, of an atom in an element.
(i) The atomic number (z) is the number of protons present in the nucleus of an atom.
(ii) Mass number (A) is sum of the number of protons (p) and the number of neutrons (n) in the nucleus of an atom.
Thus, A = n + p or = n + z. (z is atomic number.) For example the mass of carbon is 12 u because it has 6 protons and 6 neutrons, 6 u + 6 u = 12 u
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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.
Rutherford’s α-particle scattering experiment was responsible for the discovery of
Isotope of an element has
Number of valence electrons in Cl- ion are
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