Question

The total number of elements present in the 4th period of the modern periodic table is:
(A) 8
(B) 18
(C) 32
(D) 12

Answer 1

Hint: Write down the subshells present for principal quantum number(n) = 4. Add the number of electrons that can be placed in the subshells to get the total number of elements present in the 4th period.

Complete step by step solution:
-The Modern Periodic table was made by Moseley in 1932. The modern periodic table arranges elements based on increasing order of atomic number.
- The periodic table is made up of 7 periods and 18 groups.
-We will now write down subshells present for principal quantum number (n) =4
1s
2s 2p
3s 3p 3d
4s 4p 4d 4f
And so on.
There are 4 subshells namely s, p, d and f.
       - The s subshell can hold 2 electrons
       - The p subshell can hold 6 electrons
       - The d subshell can hold 10 electrons
       - The f subshell can hold 14 electrons
From the above explanation, we can conclude that the number of elements present in the 4th period is numerically equal to the total number of electrons.
Total number of electrons = 2+6+10+14 = 32

Therefore, the correct answer is option (C).

Note: While writing down the subshells for principal quantum number (n>4), keep in mind that there are only 4 subshells in which the electrons are filled as there are only 120 elements. To calculate the number of elements carefully.