(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 the modern periodic table.
(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 the modern periodic table.
(a) Modern periodic law: According to the modern periodic law, the properties of elements are a periodic function of their atomic numbers. This means, if the elements are arranged in increasing order of their atomic numbers, the elements exhibiting similar properties will repeat after regular intervals of periods.
(b) The elements are arranged in an increasing order of atomic number, and it helps in arranging the elements according to their electronic configuration. Since 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 are removed. For example:
1. 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, they can be put in one place in the same group of the periodic table.
For example, chlorine,35Cl,Cl37 which are the isotopes of Chlorine with the same atomic number 17, can be placed in one place in the same group of the periodic table.
2. Mendeleev could not explain why cobalt was placed before nickel. This problem was solved by the modern periodic law. The atomic numbers of cobalt and nickel are 27 and 28 respectively. Hence, cobalt with a lower atomic number was placed before nickel in the modern periodic table.
3. Position of hydrogen: Hydrogen has been placed at the top of group 1, above the alkali metals in the modern periodic table because the electronic configuration of hydrogen is similar to those of alkali metals. Both, 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. This is because elements are placed in the increasing order of their atomic numbers. Atomic numbers are always whole numbers and cannot be in decimals, as half an electron or half a proton cannot exist.
(e) Henry Moseley is the scientist who prepared the modern periodic table.
(a) Modern periodic law: According to the modern periodic law, the properties of elements are a periodic function of their atomic numbers. This means, if the elements are arranged in increasing order of their atomic numbers, the elements exhibiting similar properties will repeat after regular intervals of periods.
(b) The elements are arranged in an increasing order of atomic number, and it helps in arranging the elements according to their electronic configuration. Since 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 are removed. For example:
1. 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, they can be put in one place in the same group of the periodic table.
For example, chlorine,35Cl,Cl37 which are the isotopes of Chlorine with the same atomic number 17, can be placed in one place in the same group of the periodic table.
2. Mendeleev could not explain why cobalt was placed before nickel. This problem was solved by the modern periodic law. The atomic numbers of cobalt and nickel are 27 and 28 respectively. Hence, cobalt with a lower atomic number was placed before nickel in the modern periodic table.
3. Position of hydrogen: Hydrogen has been placed at the top of group 1, above the alkali metals in the modern periodic table because the electronic configuration of hydrogen is similar to those of alkali metals. Both, 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. This is because elements are placed in the increasing order of their atomic numbers. Atomic numbers are always whole numbers and cannot be in decimals, as half an electron or half a proton cannot exist.
(e) Henry Moseley is the scientist who prepared the modern periodic table.
