Classification of elements

 Give reason questions.

1. It is necessary to classify elements.

​Reason:

There are 118 known elements, each possessing distinct physical and chemical properties. Classifying elements into groups based on their shared characteristics makes it systematic and significantly easier to study their behaviors, chemical trends, and reactions without having to memorize each element individually.

​2. Sodium and chlorine belong to different groups, but both have a valency of 1.

​Reason:

Valency is determined by the number of electrons an atom loses, gains, or shares to achieve a stable octet (outer electron shell):

  • ​Sodium (\text{Na}): Located in Group 1 with an electronic configuration of 2, 8, 1. It loses 1 electron to become stable, so its valency is 1.
  • ​Chlorine (\text{Cl}): Located in Group 17 with an electronic configuration of 2, 8, 7. It gains 1 electron to complete its shell, so its valency is also 1.

​Since both atoms transfer or share a single electron to achieve stability, both have a valency of 1 despite being in different groups.

​3. Products are different from reactants.

​Reason:

During a chemical reaction, the original chemical bonds holding the reactants together break, and entirely new bonds are formed to construct the products. Because the arrangement of atoms changes, the resulting products have distinct chemical structures and entirely different physical and chemical properties from the starting reactants.

​4. Periodic table has made it easier to study elements.

​Reason:

The periodic table organizes all elements logically in order of increasing atomic number into rows (periods) and columns (groups). Elements within the same group share similar outer electron configurations and chemical properties, allowing scientists to easily predict periodic trends (like reactivity, atomic size, and metallic character) rather than studying each element in isolation.

​5. The position of metals and non-metals are different in the periodic table.

​Reason:

Metals and non-metals have fundamentally different electronic structures and properties:

  • ​Metals: Have 1 to 3 valence electrons, low ionization energy, and easily lose electrons (electropositive). Therefore, they are positioned on the left and center of the periodic table.
  • ​Non-metals: Have 4 to 7 valence electrons, high electron affinity, and tend to gain or share electrons (electronegative). Therefore, they are placed on the top-right side of the periodic table.

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