An element X has six electrons in its outer shell and forms a diatomic molecule. Class 9

An element X has six electrons in its outer shell and forms a diatomic molecule. Class 9

Question 1.

An element X has six electrons in its outer shell and forms a diatomic molecule. Class 9

(i) Why would that be so?

(ii) What kind of bond would it form?

(iii) Draw the structure of the molecule it would form.

(iv) A certain other element Y has two electrons in its second shell. Draw the structure of the molecule that X would form with Y.

Answer:

Element X has 6 valence electrons and needs 2 more to complete its octet. This is oxygen (O), atomic number 8.

(i) X has 6 valence electrons and needs 2 more to complete its octet, so two X atoms share electrons and form a diatomic molecule.

(ii) It forms a covalent bond by sharing electrons.

(iii) Structure: X₂ molecule with a double covalent bond between the two atoms (X = X). xx • • xx O == O xx • • xx

(iv) Element Y has 2 valence electrons, so it forms an ionic compound with X. Y donates 2 electrons and X gains 2 electrons, forming YX (like MgO) with ionic bonding. • • • • • • O == C == O • • • • • •

Question 2.

You want to design a new ionic compound, where the total positive charge is 6+ and the total negative charge is 6 -. Which of the following combinations gives the correct number of ions? Class 9

(i) 2 Al³⁺ and 3 Cl^-

(ii) 3 Mg²⁺ and 1 PO₄^3-

(iii) 2 Fe³⁺ and 3 O^2-

(iv) 3 Ca²⁺ and 2 SO₄^2-

Answer:

Check total positive and negative charges:

(i) 2 Al³⁺: total positive = 2 × 3 = 6+; 3 Cl^-: total negative = 3 × 1 = 3-. Not balanced (6+ ≠ 3-).

(ii) 3 Mg²⁺: total positive = 3 × 2 = 6+; 1 PO₄^3-: total negative = 1 × 3 = 3-. Not balanced.

(iii) 2 Fe³⁺: total positive = 2 × 3 = 6+; 3 O^2-: total negative = 3 × 2 = 6-. Balanced! Total positive = 6+, total negative = 6-.

(iv) 3 Ca²⁺: total positive = 3 × 2 = 6+; 2 SO₄^2-: total negative = 2 × 2 = 4-. Not balanced.

Answer: (iii) 2 Fe³⁺ and 3 O^2-