Question

In the modern periodic table, calcium (atomic number $20$) is surrounded by elements with atomic numbers$12,19,21,38$. Which of these have physical and chemical properties resembling calcium?

Answer 1

Modern periodic table:

1. The periodic table is a tabular arrangement of elements in groups and periods that emphasizes regular trends in element properties.
2. Elements containing the same number of valence electrons in their outermost shell, exhibit similar properties.
3. Electronic configuration of calcium$=1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}4{\mathrm{s}}^2$ therefore, valence electron in calcium$=2$
4. Electronic configuration of an element with an atomic number$=12$ i.e. Magnesium $=1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^2$ therefore, valence electron in Magnesium$=2$
5. Electronic configuration of an element with an atomic number$=19$ i.e. Potassium$=1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}4{\mathrm{s}}^1$, therefore, valence electron in Potassium$=1$
6. Electronic configuration of an element with an atomic number$=21$ i.e. Scandium$=1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}4{\mathrm{s}}^{2}4{\mathrm{p}}^1$, therefore, valence electron in Scandium$=1$
7. Electronic configuration of an element with an atomic number$=38$ i.e. Strontium$=1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}4{\mathrm{s}}^{2}3{\mathrm{d}}^{10}4{\mathrm{p}}^{6}5{\mathrm{s}}^2$, therefore, valence electron in Strontium$=2$
8. Only the element with atomic number $12$ and the element with atomic number $38$ contain the same number of valence electrons as calcium so they will show the same properties.

Therefore, Calcium is similar in properties to the element having an atomic number $12$ and to the element having the atomic number $38$.