Question

(a) What were the two achievements of Mendeleev's periodic table? What was the basis of classification of elements in it?
(b) An element X (2, 8, 2) combines separately with (NO₃)⁻, (SO₄)²⁻ and (PO₄)³⁻ radicals.
(c) To which group of the periodic table does the element 'X' belong? Will it form covalent or ionic compound? Why?
(d) To which period of the periodic table does the element X belong? Give reason for your answer.
(e) Write the name and symbol of element X. Also give the name and symbol of another element which belongs to the same period as element X.

Answer 1

(a) Achievements of the Mendeleev's periodic table are as under: (You can write any two)
(i) The systematic study of elements
(ii) Prediction of new elements
(iii) Correction of atomic mass

Elements were classified on the basis of hydrides and oxides formed by elements.

(b) Element X with electronic configuration is 2, 8 ,2
So the number of valence electrons of X = 2
Number of valence electrons = valency of X
Valency of the nitrate ions (NO₃)^- = 1, so compound formed with element X and nitrate will be M(NO₃)_2.
Valency of the sulphate ions (SO₄)^-2 = 2, so compound formed with element X and sulphate will be MSO_4.
Valency of the phosphate ions (PO₄)^-3 = 3, so compound formed with element X and phosphate will be M₃(PO₄)_2.

(c) The atomic number of element X is 12, valence electrons are 2. Thus, X belongs to the second group of the periodic table.
It will form an ionic bond, to attain noble gas configuration it will easily lose two electrons.

(d) The atomic number of element X is 12, valence electrons are 2. Thus, X belongs to the third period of the periodic table.

(e) The atomic number of element X is 12, which resembles magnesium (Mg) of the periodic table.
Another element which belongs to the same period will be sodium (Na).