Write the formulae of the compounds formed from the following pairs of ions. Class 9

Write the formulae of the compounds formed from the following pairs of ions. Class 9

Question 1.

Write the formulae of the compounds formed from the following pairs of ions. Class 9

(i) Ca²⁺ and Br^-

(ii) Al³⁺ and CO₃^2-

(iii) K⁺ and SO₄^2-

(iv) NH₄⁺ and Cl^-

Answer:

(i) Ca²⁺ and Br^- → CaBr₂ (Charges: 2+ and 1-; calcium bromide)

(ii) Al³⁺ and CO₃^2- → Al₂(CO₃)₃ (Charges: 3+ and 2-; aluminium carbonate)

(iii) K⁺ and SO₄^2- → K₂SO₄ (Charges: 1+ and 2-; potassium sulfate)

(iv) NH₄⁺ and Cl^- → NH₄Cl (Charges: 1+ and 1-; ammonium chloride)

Question 1.

Which of the following, in Fig., correctly represents Cl^- ion (Atomic number of chlorine = 17). Class 9

Answer:

Chlorine (atomic number 17) has the electronic configuration 2, 8, 7. It has 7 electrons in its valence shell (third shell). When chlorine gains one electron to form the chloride ion (CL), it has 18 electrons total. The electronic configuration of CL becomes 2, 8, 8. So the correct diagram should show: 17 protons in the nucleus 18 electrons total First shell: 2 electrons Second shell: 8 electrons Third shell: 8 electrons The correct option is (ii) - which shows an atom with three shells having 2, 8, and 8 electrons (total 18 electrons), representing the CL ion with a complete outermost shell.