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(a) State modern periodic law.(b) How does the electronic configuration of the atom of an element relate to its position in the modern periodic table?
(c) How could the modern periodic law remove various anomalies of Mendeleev’s periodic table? Explain with examples.
(d) Is it possible to have an element having atomic number 1.5 placed between hydrogen and helium ?
(e) Name the scientist who prepared modern periodic table.
(a) According to the modern periodic law, the properties of elements are a periodic function of their atomic numbers.
(This law means that if the elements are arranged in increasing order of their atomic numbers, the elements having similar properties will repeat after regular intervals of periods.)
(b) The elements are arranged in increasing order of atomic number and helps in arranging the elements according to their electronic configuration. As elements having the same number of valence electrons show similar chemical properties, they are placed under the same group.
(c) As the modern periodic law is based on the atomic numbers of elements, all the anomalies of Mendeleev's periodic table were removed. For example:
- The position of isotopes could be explained, which Mendeleev's periodic table failed to explain. As all the isotopes of an element have the same atomic number, so they could be placed under the same group in a periodic table. For example, Cl-35 and Cl-36, the isotopes of Chlorine with the same atomic number 17, can be placed in the same group of the periodic table.
- Mendeleev could not explain why cobalt was placed before nickel. This problem was solved by the modern periodic law as the atomic numbers of cobalt and nickel are 27 and 28, respectively. Therefore, cobalt with a lower atomic number was placed before nickel in the modern periodic table.
- The hydrogen element has been placed at the top of group 1, above the alkali metals because the electronic configuration of hydrogen is similar to those of alkali metals. Both, hydrogen as well as alkali metals have 1 valence electron each.
(d) It is not possible to place an element with an atomic number of 1.5 between hydrogen and helium because elements are placed in the increasing order of their atomic numbers.
Moreover, atomic numbers are always whole numbers and cannot be in decimals, as half an electron or half a proton cannot exist.
(e) Niels Bohr prepared the modern periodic table.
Updated on: 10-Oct-2022
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