Valency across Periods and Groups - UNSOLVED PRACTICE SET
Chapter: Periodic Classification of Elements | Topic: Valency across Periods and Groups
VALENCY ACROSS PERIODS AND GROUPS - UNSOLVED PRACTICE SET
Topic: Valency across Periods and Groups
Multiple Choice Questions
Q1. Valency of an element is determined by:
- The number of protons
- The number of valence electrons
- The total number of electrons
- The number of neutrons
Q2. The valency of elements in Group 1 is:
- 1
- 2
- 3
- Variable
Q3. Across a period from left to right, valency:
- Increases continuously
- Decreases continuously
- First increases and then decreases
- Remains constant
Q4. The valency of oxygen is:
- 1
- 2
- 4
- 3
Q5. Elements in Group 17 (halogens) have a valency of:
- 1
- 2
- 7
- 8
Q6. The maximum valency shown by elements in Period 2 is:
- 2
- 3
- 4
- 8
Short Answer Questions
Q7. Define valency. How is valency related to the number of valence electrons for elements in Groups 1 to 14?
Q8. Why does valency first increase and then decrease across a period? Illustrate with Period 2 elements.
Q9. What is the valency of noble gases? Why do they have zero valency?
Q10. Why do all elements in Group 2 have a valency of 2? Give an example.
Q11. Your chemistry teacher writes the formulae NaCl, MgCl₂, and AlCl₃ on the board. She asks you to explain why sodium, magnesium, and aluminium form compounds with different numbers of chlorine atoms. How does this relate to their position in the periodic table?
Q12. How does the valency of elements change down a group? Explain with the example of Group 1 elements.
Long Answer Questions
Q13. Explain the variation of valency across a period and down a group. Use Period 3 (Na to Ar) and Group 1 (Li to K) as examples. Why do noble gases have zero valency? How does the concept of valency help in predicting the formulae of compounds?tion here...
Q14. Describe how valency is related to the electronic configuration of elements. For the elements in Period 2 (Li to Ne), show how valency is determined by the number of valence electrons. Explain why carbon shows a valency of 4 while nitrogen shows a valency of 3.
Q15. During a group project, you are asked to predict the formulae of compounds formed by elements in Period 3 with chlorine.
(a) Write the expected formulae for the compounds formed by Na, Mg, Al, Si, P, and S with chlorine.
(b) Explain how the valency of each element determines the formula.
(c) Why does phosphorus form both PCl₃ and PCl₅? What does this tell you about the concept of variable valency?
(d) Argon does not form any compound with chlorine. Why?
Numerical / Application-Based Problems
Q16. Consider the elements in Period 2: Li (2,1), Be (2,2), B (2,3), C (2,4), N (2,5), O (2,6), F (2,7), Ne (2,8).
(a) Calculate the valency of each element.
(b) Plot a graph of valency vs. atomic number for these elements.
(c) What pattern do you observe? Explain why valency follows this pattern.
Q17. A student is given the following elements and asked to predict their compounds with oxygen:
Table
Element Group Valency with Oxygen
Na 1 ?
Mg 2 ?
Al 13 ?
Si 14 ?
P 15 ?
S 16 ?
(a) Complete the table by writing the formulae of oxides for each element.
(b) Explain how the valency of each element determines the formula of its oxide.
(c) Why does the valency with oxygen not always match the group number for Groups 15 and 16?
Q18. An element X belongs to Group 14 and Period 3. Another element Y belongs to Group 16 and Period 3.
(a) Identify elements X and Y.
(b) Predict the valency of X and Y.
(c) Write the formula of the compound formed between X and Y.
(d) Element Z belongs to Group 1 and Period 4. Predict the formula of the compound formed between Z and Y. How does this compound differ from the compound formed between X and Y in terms of bonding?