Question

How does the electronic configuration of an atom relate to its position in the Modern Periodic Table?

Answer 1

Periodic table:

• The periodic table is a tabular display of the chemical elements.
• The elements in the periodic table are arranged in order of atomic number.
• A period is the elements that are arranged in a horizontal row of the periodic table.
• A group is the elements that are arranged in a vertical row of the periodic table.

Identification of period:

• The electron configuration of an atom is the distribution of electrons in the increasing order of energy of atomic orbitals.
• It determines the number of valence electrons and the number of shells present.
• The number of shells in an element represents the period number.

Identification of group:

• The group number can be determined by the number of valence electrons and the subshell to which it belongs.
• The block of an element corresponds to the orbital which receives the last electron
• If the element is in s block, then the group number is equal to the number of valence electrons.
• If the element is in the p block, then the number of the group can be determined by adding 10 to the number of valence electrons.
• If the element is in the d block, then the number of the group can be determined by adding the number of electrons in $(\mathrm{n}-1)\mathrm{d}$ subshell to the number of electrons in $\mathrm{ns}$ subshell.
• If the element is in the f block, then the group is always 3, since these elements are the formal members of group 3

Example:

• The atomic number of Nitrogen is 7 and thus the electronic configuration is $\mathrm{N}=1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^3$
• The number of shells is 2 which shows that it belongs to the 2nd period.
• The number of valence electrons is 3 and the last electron enters into p-orbital, so it belongs to the p-block.
• To calculate the group number for the p-block element add 10 to the total electrons in valence shell of the element.
• Here total valence shell electrons are 5. So group number will be $10+5=15$
• Hence, Nitrogen ($\mathrm{N}$) belongs to the 2nd period and 15th group.

Therefore, we can calculate an element’s group number, period number, and thereby the position in the periodic table by knowing the electronic configuration.