Activity 1.3

1. Consider isotopes of oxygen ¹⁶O and ¹⁸O. Would you able to place them in Mendeleev’s periodic table?

Ans. Yes, In Mendeleev’s Periodic table elements are arranged in the increasing order of atomic masses. Therefore, we can place isotopes of oxygen ¹⁶O and ¹⁸O in Mendeleev’s periodic table in two different position.

2. Find resemblance between hydrogen and alkali metals by writing compounds of both with chlorine, sulphur and oxygen.

Ans. Hydrogen and other alkali metal react with non – metals (O, S and Cl),

Hydrogen forms: H₂O, H_­2S, HCl.

Sodium (Alkali metal) forms: Na₂O, Na₂S, NaCl.

Compounds of Hydrogen	Compounds of Sodium
HCl (Hydrogen Chloride) H2S (Hydrogen Sulphide) H2O (Hydrogen Oxide)	NaCl (Sodium Chloride) Na2S (Sodium Sulphide) Na2O (Sodium Oxide)

      

 As seen above compounds of hydrogen and compounds of sodium with halogen, sulphur and oxygen have similar formulae. This is because the electronic configuration of hydrogen resembles that of alkali metals.

3. Find out a pair of elements from the periodic table where higher mass element is placed before lower mass element.

Ans. 1. Argon (40) is placed before potassium (39.1).

2. Vanadium (V) having atomic mass 50.94 is placed before Chromium (Cr) having atomic mass 50.20.

3. Cobalt (Co) having atomic mass 58.93 is placed before Nickel (Ni) having atomic mass 58.71