Question

On the basis of the table of Mendeleev’s Periodic Table

(a) Name the element which is in

(i) 1^st group and 3^rd period.

(ii) 17^th group and 2^nd period.

(b) Suggest the formula for the following:

(i) Oxide of nitrogen

(ii) Hydride of oxygen

(c) In group VIII of periodic table, why does cobalt with atomic mass 58.93 appeal before nickel having atomic mass 58.71?

(d) Besides gallium, which two other elements have since been discovered for which Mendeleev had left gaps in his periodic table?

(e) Using atomic masses of Li, and K, find the average atomic mass of Na. State the conclusion drawn from this activity.

Answer 1

(a) (i) Sodium (ii) Fluorine

(b) (i) N₂ O₅ (ii) H₂O

(c) Atomic number of CO (27) is lower than Ni (28).
Also CO resembles with Rh and Ir whereas ‘Ni’ resembles with Pd and Pt.

(d) Germanium and scandium

(e)

Li	Na	K
6.939	22.99	39.102

Average atomic mass of Na 

= \(\frac{6.939 +39.102}{2}\) = 23.0205

The atomic mass of Na is the average atomic mass of Li and K and these elements resemble with each other.