Class 10 Science Chapter 2 - Periodic Classification of Elements
Comprehensive exercise solutions with logic-based explanations, modern periodic table concept, electronic configurations, and board-exam patterns.
Q1. Match the Columns
Rearrange Column 2 and 3 to match with Column 1.
| Column 1 | Description (Corrected) | Scientist |
|---|---|---|
| i. Triad | Average of atomic masses of 1st and 3rd | Dobereiner |
| ii. Octave | Properties of 8th similar to 1st | Newlands |
| iii. Atomic Number | Positive charge on the nucleus | Moseley |
| iv. Period | Sequential change in properties | Mendeleev |
| v. Nucleus | Concentrated mass and positive charge | Rutherford |
| vi. Electron | Lightest and negatively charged particle | Thomson |
Q2. Choose the Correct Option
The number of electrons in the outermost shell of alkali metals is...
- A. 1
- B. 2
- C. 3
- D. 7
Logic: Alkali metals belong to group 1, meaning they have 1 valence electron.
Alkaline earth metals have valency 2. This means their position is in:
- A. Group 2
- B. Group 16
- C. Period 2
- D. d-block
Logic: Group 2 elements are alkaline earth metals with 2 valence electrons.
Q3. Electronic Configuration Context
Electronic Configuration: 2, 8, 2.
- What is the atomic number?
- What is the group?
- To which period does it belong?
- Which element resembles it? (Options: N[7], Be[4], Ar[18], Cl[17])
2. Group: 2 (2 valence electrons)
3. Period: 3 (3 occupied shells)
4. Resembles: Beryllium (Be), as both are in group 2.
Q4. Electronic Configuration analysis
Which of Na, P, Cl, Si, Mg has the largest atomic radius?
Answer:Scientific Reason: These elements belong to the same period. Atomic radius decreases from left to right as atomic number increases (nuclear charge increases). Na is at the start, hence it's the largest.
Interactive: Element Finder (1-20)
Test the electronic configurations and positions of standard elements.
Q6. Short Notes
- Groups: There are 18 vertical columns. Elements in a group have same valence electrons.
- Periods: There are 7 horizontal rows. Elements in a period have sequential atomic numbers.
- Blocks: S, P, D, and F blocks divide elements based on electron shell filling.
- Zig-Zag line: Separates metals (left) from non-metals (right), with metalloids along the border.
Q7. Scientific Reasons
Question: Give scientific reason: Atomic radius goes on decreasing while going from left to right in a period.
Exam Answer:1. As we move across a period, atomic number increases by one unit consecutively.
2. This adds one proton to the nucleus, increasing positive nuclear charge.
3. However, electrons are added to the same outermost shell.
4. Due to increased charge, attraction between nucleus and electrons increases, pulling them closer.
5. Thus, the atomic radius decreases.
Practice Quiz
Test your knowledge! Answer 15 questions sequentially.
FAQs
It states that "Properties of elements are a periodic function of their atomic numbers."
Noble gases have 0 valency because they have a complete octet/duplet and do not react easily.
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