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Vidaara.orgClass 10 · Chemistry
CodeVID-C10-05-T2-01
Assignment — The Modern Periodic Table & Periodic Law
Chapter: Periodic Classification of Elements
Topic: The Modern Periodic Table & Periodic Law
Maximum Marks: 30
Time: 60 minutes
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.
The modern periodic law is based on:
  • A.atomic mass
  • B.atomic number
  • C.number of neutrons
  • D.density
2.
The number of groups in the modern periodic table is:
  • A.7
  • B.8
  • C.18
  • D.9
3.
An element with configuration 2, 8, 7 lies in group:
  • A.7
  • B.17
  • C.1
  • D.18
4.
Elements in the same group have the same number of:
  • A.shells
  • B.neutrons
  • C.valence electrons
  • D.protons
5.
The number of elements in the second period is:
  • A.2
  • B.8
  • C.18
  • D.32
Section B — Short Answer (2 marks) 3 × 2 = 6 marks
6.
State the modern periodic law and name the scientist whose work led to it.
7.
An element has atomic number 12. Find its period and group.
8.
How does the modern periodic table place isotopes of an element?
Section C — Short Answer (3 marks) 2 × 3 = 6 marks
9.
Explain how the period and group of an element are decided from its electronic configuration, using calcium (Z = 20) as an example.
10.
How did the modern periodic table resolve the anomaly of cobalt and nickel?
Section D — Long Answer (5 marks) 1 × 5 = 5 marks
11.
Describe the structure of the modern periodic table (groups and periods) and explain, with two examples, how electronic configuration fixes an element's position. State two anomalies of Mendeleev's table that the modern table resolves.

Answer Key

Section A — Multiple Choice Questions
  1. (B) atomic number
  2. (C) 18
  3. (B) 17
  4. (C) valence electrons
  5. (B) 8
Section B — Short Answer (2 marks)
  1. The properties of elements are a periodic function of their atomic numbers; it followed from Moseley's work on atomic number.
  2. Configuration 2, 8, 2; three shells means Period 3 and two valence electrons means Group 2 (magnesium).
  3. All isotopes have the same atomic number, so they are placed together in one single position.
Section C — Short Answer (3 marks)
  1. The number of occupied shells gives the period and the number of valence electrons gives the group. Calcium is 2, 8, 8, 2: four shells means Period 4, and two valence electrons means Group 2.
  2. By atomic mass, nickel is lighter, yet Mendeleev placed cobalt first to match properties. By atomic number, cobalt (Z = 27) naturally comes before nickel (Z = 28), so arranging by atomic number resolves the anomaly.
Section D — Long Answer (5 marks)
  1. The modern table has 18 vertical groups and 7 horizontal periods. The number of occupied shells equals the period number and the number of valence electrons decides the group for main-group elements. Example 1: sodium (2, 8, 1) has 3 shells (Period 3) and 1 valence electron (Group 1). Example 2: chlorine (2, 8, 7) has 3 shells (Period 3) and 7 valence electrons (Group 17). Anomalies resolved: (i) reversed mass pairs such as Ar (Z = 18) before K (Z = 19) now sit correctly by atomic number; (ii) isotopes, having the same atomic number, occupy a single position instead of needing separate places.
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