Question

️ Assignment No 2.4
️Modern Periodic table
i) Write electronic configuration of Na, Al, C, O, K, Ca
ii) Write short notes:
1) Structure of modern periodic table
2) Position of isotopes in Mendeleev's and modern periodic table.
3)​

Answer 1

Electronic Configuration of :

• Na -
• ${1s}^{2} {2s}^{2} {2p}^{6} {3s}^{1}$
• Al -
• ${1s}^{2} {2s}^{2} {2p}^{6} {3s}^{2} {3p}^{1}$
• C -
• ${1s}^{2} {2s}^{2} {2p}^{2}$
• O -
• ${1s}^{2} {2s}^{2} {2p}^{4}$
• K -
• ${1s}^{2} {2s}^{2} {2p}^{6} {3s}^{2} {3p}^{6} {4s}^{1}$
• Ca -
• ${1s}^{2} {2s}^{2} {2p}^{6} {3s}^{2} {3p}^{6} {4s}^{2}$

Structure of modern periodic table :

Modern periodic law : The physical and chemical properties of the elements are the periodic functions of their electronic configuration of atoms. This is call modern periodic law. The modern periodic law is constructed based on MOSELEY experiment.

• The modern periodic table has 18 vertical columns known as groups and 7 horizontal rows known as periods.
• The elements with similar outer shell electronic configuration in their atoms are in the same column called groups.
• Groups are represented by Roman numeral with letters A and B (or) according to the latest recommendation of the IUPAC groups are represented by Arabic numerals 1 to 18.
• Within the group elements are arranged in order of their increasing principal quantum number.
• Periods are represented by Arabic numerals 1 to 7.
• The number of main shells present in the atom of particular element decides to which period it belongs.
• Every period starts with a new main shell 's' subshell and ends when the main shell is filled with respect to the 's' and 'p' subshells (except first period).
• First period starts with K shell. the first main shell K contains only one subshell, the (1s). It contains only two elements.
• Second period starts with the second main shell (L). L- shell has to subshells, namely 2s and 2p. It contains 8 elements.
• Similarly third period has eight elements Na to Ar (filling 3s and 3p) filled in the M shell.
• 4th and 5th period have 18 elements filling 4s, 3d, 4p and 5s, 4d and 5p (filled in the N and O shells).
• Sixth period consists of 32 elements (Cs to Rn). Seventh period is incomplete period.
• Lanthanoids and actinoids are kept separately at the bottom of the periodic table based on valence electronic configuration and different properties from other group.

Position of isotopes in Mendeleev's and modern periodic table :

Isotopes have the same atomic number, similar chemical properties but different atomic masses. Based on the periodic law, an isotope is an element, which must have a separate place in the periodic table. However, there are no places for isotopes in Mendeleev's and modern periodic table.

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