Question

(a) How were the positions of isotopes of an element decided in the modern periodic table?
(b) How were the positions of cobalt and nickel resolved in the modern periodic table?
(c) where should hydrogen be placed in the modern periodic table? Give reason for your answer.

Answer 1

Answer:

a)  Modern periodic table is based on the modern periodic law which states that the properties of the elements are the periodic function of their atomic numbers. Isotopes of the same element have same atomic numbers so they are alloted the same position in the modern periodic table. Hence, this was an advantage of modern periodic table that it was able to solve the problem of position of isotopes.

Example: If we take two isotopes of the same element carbon 126C and 146C, the atomic number is same as 6 so both of them will be represented in one position only at not in two different positions.

b) Cobalt has an atomic number 27 and nickel 28. According to the modern periodic law elements are arranged in the order of increasing atomic number. So, cobalt is placed before nickel even though their atomic masses are not in increasing order.

c)Hydrogen is placed in 1st group which belongs to alkali metals because it has a valence electron and it acts as an alkali element.

Explanation:

Answer 2

Explanation:

(a) In the periodic table, the component isotopes are also not given a separate area.

• That's because isotopes has the similar atomic number and specific atomic mass, and depending on the atomic number of dimensions, the current periodic table is based.
• Hence, the components should be grouped as per their atomic mass to give it a separate area.

(b) According to Mendeleev's classification, elements are organized in an ascending order of atomic masses, but cobalt has been put before nickel, with a higher atomic mass.

• Cobalt has a 58.9 atomic mass and nickel has a 58.7 atomic mass which is marginally lower than cobalt. This argument could not be answered by Mendeleev.
• The scientific periodic table solved this problem. In keeping with scientific periodic law, the elements are listed in the ascending order of their numbers of atom.
• Cobalt and nickel atomic numbers are 27,and 28, respectively. So cobalt would come before nickel with lower atomic number.

(c) In general, The hydrogen is regarded as a special element and positioned by itself at the head of the periodic table. The role of hydrogen in the periodic table is uncertain, since in some of its properties it resembles both halogens metals and alkali.

• Nevertheless, as its electronic configuration is similar to that of alkali metals, it is classified in the first category, particularly the alkali metals in the modern periodic table.
• Due to the tiny size of hydrogen, it exhibits characteristics that are different from the alkali metals.