Classification of elements (Modern periodic table)

August 24, 2017 Sushil Humagain Chemistry 0

  • Modern periodic table was proposed by Henry Moseley in 1963. He found that the atomic number is the more fundamental property which led to the formulation of Moseley’s Periodic Law which can be stated as follows.

The physical and chemical properties of elements are the periodic function of their increasing atomic number.

 

  1. Alkali metals: Group IA
  • They react with water to form alkalies and hydrogen gas.

e.g. 2Na + 2H2O ———> 2NaOH +H2

2K + 2H2O ———> 2KOH +H2

  1. Alkaline Earth metals: Group IIA
  • Their oxides are abundant in the Earth’s crust which when dissolved in water are alkaline in nature.

e.g. MgO + H2O ———> Mg(OH)2

CaO + H2O ———> Ca(OH)2

  1. Halogens: Group VIIA
  • They react with alkali metals (Group IA) to form corresponding halides (salts).

e.g. 2Na + Cl2 ———> 2NaCl

2K + I2 ———> 2KI

  1. Inert/Noble gases: Group 0
  • They have stable electronic configuration i.e. duplet (He) and octet state (Ne, Ar etc.) so they don’t react with other elements.
  1. Lanthanides and Actinides:
  • 15 elements from 57La (Lanthanum) to 71Lu (Lutetium) and other 15 elements from 89Ac (Actinium) to 103Lw (Lawrencium) are f-block or Inner transition elements
  1. Normal or Representative elements are IA, IIA, IIIA, …..VIIA, 0
  2. Transition or d-block elements are IB, IIB,………VIIB, VIII
  3. s-block elements are (IA, IIA), p-block elements are (IIIA to VIIA, 0) and metalloids are B, Si, As (Arsenic), Ge (Germanium) and Sb (Antimony).
  4. Reactivity down the Group:

     Metals (IA, IIA, IIIA)

  • Reactivity increases down the group due to increase in electropositivity.
  • Atomic size increases.
  • Nuclear attraction between the protons and valence electrons decreases
  • Hence, it is easy to lose electrons down the group.
  • Group IA is the group of the most reactive metals.

     Non-metals (VA, VIA, VIIA)

  • Reactivity decreases down the group due to decrease in electronegativity.
  • Atomic size increases.
  • Nuclear attraction between the protons and incoming electron decreases.
  • Hence, there is difficulty to gain electrons down the group.
  • Group VIIA is the group of the most reactive non-metals.

      Identification of elements:

  • Group= Number of valence electrons
  • Period= Number of shells/orbitals
  • Block= The orbital in which the last electron of avalence shell enters
  • Valency= Group number (for IA to IVA) and 8-group number (for VA to VIIA)

 

Classification of elements (Modern periodic table)