☰
The Fundamental Unit of Life
What is atomic number? How has this concept improved the definition of an element?
(i) Atomic number of an element is equal to the number of protons present in the nucleus of its atom.
∴
Atomic number = Number of unit positive charges on the nucleus.
Since the atom as a whole is electrically neutral, therefore, atomic number is the same as the number of electrons around the nucleus of an atom.
(ii) Atomic number gives the position of the element in the periodic table. In terms of atomic number an element can now be defined as a substance comprising of atoms all of which have the same atomic number.
Sponsor Area
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.
Rutherford’s α-particle scattering experiment was responsible for the discovery of
Sponsor Area
Sponsor Area