Valency - UNSOLVED PRACTICE SET

Q7. Define valency. How is valency related to the number of electrons in the outermost shell of an atom?

Q8. Determine the valency of the following elements from their electronic configurations: (i) 2, 8, 3 (Aluminium), (ii) 2, 8, 8 (Argon), (iii) 2, 1 (Lithium), (iv) 2, 8, 6 (Sulphur).

Q9. Your teacher explains valency using the analogy of a student who needs to give away or borrow pens to complete a set of 8. If a student has 6 pens, how many does he need to borrow? If another student has 1 pen, how many can he give away? Relate this to the valency of sulphur and sodium.

Q10. Why do elements with completely filled outermost shells (like noble gases) have zero valency? Explain with reference to stability.

Q11. Write the electronic configuration and determine the valency of: (i) Fluorine (Z = 9), (ii) Potassium (Z = 19), (iii) Calcium (Z = 20), (iv) Nitrogen (Z = 7).

Q12. How does valency help in predicting the formula of a compound? Explain with the example of magnesium oxide (MgO).

Q13. Define valency and explain how it is determined from the electronic configuration of an atom. Describe the two ways in which an atom can achieve a stable electronic configuration: (i) by losing electrons, and (ii) by gaining electrons. Give examples of elements that lose electrons, gain electrons, and share electrons to achieve stability.

Q14. A student is confused about why some elements have variable valency (like iron having valency 2 and 3) while others have fixed valency. Help the student by:

(a) Explaining what variable valency means.

(b) Giving two examples of elements with variable valency and their different valencies.

(c) Explaining why transition metals show variable valency.

(d) Writing the formulae of ferrous oxide and ferric oxide to illustrate variable valency of iron.

Q15. "Valency is the language that atoms use to communicate and form bonds with each other." Discuss this statement by explaining: (i) how valency determines the formula of compounds, (ii) how it predicts whether an element will form ionic or covalent bonds, (iii) its role in understanding the periodic table and periodic trends, and (iv) its practical importance in chemistry, pharmacy, and materials science.

Q16. The following table gives information about several elements:

Table

Element Atomic Number Electronic Configuration

A 3 2, 1

B 9 2, 7

C 11 2, 8, 1

D 12 2, 8, 2

E 15 2, 8, 5

F 17 2, 8, 7

G 18 2, 8, 8

(a) Determine the valency of each element.

(b) Identify which elements will form cations and which will form anions.

(c) Predict the formulae of compounds formed between: (i) A and F, (ii) C and F, (iii) D and F, (iv) B and D.

(d) Which element will not form any compound? Why?

(e) If Element A is lithium and Element F is chlorine, calculate the mass of lithium chloride (LiCl) formed when 7 g of lithium reacts completely with chlorine.

Q17. A pharmaceutical company manufactures common salt (NaCl) and baking soda (NaHCO₃).

(a) Determine the valency of sodium from its electronic configuration (Z = 11).

(b) Determine the valency of chlorine from its electronic configuration (Z = 17).

(c) Explain why the formula of sodium chloride is NaCl and not Na₂Cl or NaCl₂.

(d) In baking soda (NaHCO₃), sodium has a valency of 1. If the company wants to make sodium sulphate (Na₂SO₄), explain why the formula requires 2 sodium atoms.

(e) Calculate the mass of sodium required to produce 100 kg of sodium chloride.

Q18. In a school science fair, students create models to demonstrate valency and bonding.

(a) A student uses clay balls to represent atoms. If red balls represent atoms with 1 valence electron and blue balls represent atoms with 7 valence electrons, how many red and blue balls are needed to model NaCl?

(b) If green balls represent atoms with 4 valence electrons, how can a student model the bonding in methane (CH₄) using green and white (1 valence electron) balls?

(c) The student wants to model diamond, where each carbon atom is bonded to 4 other carbon atoms. How many bonds does each carbon atom form, and what does this tell you about carbon's valency in diamond?

(d) In graphite (used in pencil leads), each carbon atom is bonded to 3 other carbon atoms. What is carbon's valency in graphite, and how does this differ from diamond?

(e) Why is understanding valency important for materials scientists developing new materials for Indian industries?