Vidaara.orgClass 10 · Chemistry
CodeVID-C10-05-T3-01
Assignment — Trends in the Modern Periodic Table
Name: ____________________
Roll No.: __________
Date: ____________
General Instructions
- All questions are compulsory.
- Section A carries 1 mark each, Section B 2 marks, Section C 3 marks and Section D 5 marks.
- Show all working for Sections B, C and D. Only final answers are given at the end — for full solutions, raise your doubts with your teacher.
Section A — Multiple Choice Questions
5 × 1 = 5 marks
1.
Across a period from left to right, atomic size:
- A.increases
- B.decreases
- C.stays the same
- D.doubles
2.
Down a group, valency of the elements:
- A.increases
- B.decreases
- C.remains the same
- D.becomes zero
3.
The most metallic element among Li, Na and K is:
- A.Li
- B.Na
- C.K
- D.all equal
4.
Non-metallic character across a period from left to right:
- A.decreases
- B.increases
- C.stays constant
- D.becomes zero
5.
The valency of an element with configuration 2, 8, 6 is:
- A.6
- B.2
- C.4
- D.8
Section B — Short Answer (2 marks)
3 × 2 = 6 marks
6.
Why does atomic size increase down a group?
7.
How does valency change across period 3? Give the values.
8.
State how metallic character changes across a period and give the reason.
Section C — Short Answer (3 marks)
2 × 3 = 6 marks
9.
Explain why metals are found on the left and non-metals on the right of the periodic table.
10.
An element X has configuration 2, 8, 2 and element Y has 2, 8, 7. Compare their valencies and predict the formula of the compound they form.
Section D — Long Answer (5 marks)
1 × 5 = 5 marks
11.
Discuss the trends in atomic size and metallic character across a period and down a group, giving the reason for each trend in terms of nuclear charge and number of shells.
Answer Key
Section A — Multiple Choice Questions
- (B) decreases
- (C) remains the same
- (C) K
- (B) increases
- (B) 2
Section B — Short Answer (2 marks)
- A new shell is added at each step down a group, so the outermost electrons are farther from the nucleus and the atom becomes larger, despite the rising nuclear charge.
- It rises then falls: Na = 1, Mg = 2, Al = 3, Si = 4, P = 3, S = 2, Cl = 1, Ar = 0.
- Metallic character decreases across a period because atomic size falls and nuclear pull rises, so electrons are held tightly and are harder to lose.
Section C — Short Answer (3 marks)
- Across a period atomic size decreases and the pull on electrons increases, so left-side elements lose electrons easily (metals, electropositive) while right-side elements gain electrons easily (non-metals, electronegative). Hence metals lie on the left, non-metals on the right, with metalloids in between.
- X has 2 valence electrons (valency 2, loses electrons), Y has 7 valence electrons (valency 1, gains 1 electron). X loses 2 electrons to two Y atoms, so the compound is XY2 (like MgCl2).
Section D — Long Answer (5 marks)
- Atomic size: across a period it decreases because the number of shells is fixed while nuclear charge increases, pulling electrons inward; down a group it increases because a new shell is added at each step. Metallic character: across a period it decreases because the smaller size and greater nuclear pull make electrons harder to lose; down a group it increases because the larger size loosens the outer electrons, making them easy to lose. Every trend is a balance between increasing nuclear charge (pulls electrons in) and added shells (push electrons out); across a period charge wins, down a group the shells win.
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