Classification of Elements and Periodicity in Prop — Class 11 Chemistry NCERT Solutions (Free)
Free step-by-step NCERT solutions for Class 11 Chemistry chapter "Classification of Elements and Periodicity in Prop" — 7 important questions with detailed answers for CBSE board exam preparation.
TL;DR: Free step-by-step NCERT solutions for Class 11 Chemistry chapter "Classification of Elements and Periodicity in Prop" — 7 important questions with det…
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Key Questions Covered:
- Arrange the following elements in increasing order of ionization enthalpy: Be…
- What is the periodic law and modern periodic law? How does the modern periodi…
- Compare the effective nuclear charge experienced by 3s and 3p electrons in a …
- Define electron affinity. Explain why noble gases have very low (or near zero…
- What is electronegativity? Explain the Pauling scale and trends in electroneg…
- Predict whether the following compounds are ionic or covalent based on electr…
- + 1 more questions in the full chapter
Solutions Summary:
| Question | Status |
|---|---|
| Arrange the following elements in increasing order of ion… | ✓ Solved |
| What is the periodic law and modern periodic law? How doe… | ✓ Solved |
| Compare the effective nuclear charge experienced by 3s an… | ✓ Solved |
| Define electron affinity. Explain why noble gases have ve… | ✓ Solved |
| What is electronegativity? Explain the Pauling scale and … | ✓ Solved |
| Predict whether the following compounds are ionic or cova… | ✓ Solved |
Showing 6 of 7 questions
Q1: Arrange the following elements in increasing order of ionization enthalpy: Be, Mg, Ca, Sr. Give reason.
Increasing order of ionization enthalpy:
Be < Mg < Ca < Sr
Or in increasing order:
Sr < Ca < Mg < Be
Wait, let me correct this — the question asks for INCREASING order:
Decreasing order of ionization enthalpy:
Be > Mg > Ca > Sr
Increasing order of ionization enthalpy:
Sr < Ca < Mg < Be
Reason:
All these elements belong to Group 2 (Alkaline Earth Metals), moving down the group from Be to Sr.
1. As we move down the group:
→ Atomic number increases
→ ...
Q2: What is the periodic law and modern periodic law? How does the modern periodic law differ from Mendeleev's periodic law?
Periodic Law (Mendeleev's, 1869):
The properties of elements are periodic functions of their atomic weights.
When elements are arranged in order of increasing atomic weights, elements with similar properties recur at regular intervals.
Modern Periodic Law (1913):
The properties of elements are periodic functions of their atomic numbers.
When elements are arranged in order of increasing atomic number, elements with similar properties recur at regular intervals.
Key Differences:
1. Basis of Arr...
Q3: Compare the effective nuclear charge experienced by 3s and 3p electrons in a sulfur atom (S, Z = 16).
Given: Sulfur atom, Z = 16
Electron configuration of S: 1s² 2s² 2p⁶ 3s² 3p⁴
Effective Nuclear Charge (Zeff) formula:
Zeff = Z - S
where:
Z = actual nuclear charge (atomic number) = 16
S = shielding constant (number of inner electrons)
Part 1: Effective nuclear charge for 3s electron
Shielding for 3s electron:
→ Inner electrons (1s² 2s² 2p⁶): 10 electrons shield completely
→ Other 3s electron: shields 0.35 of nuclear charge
→ 3p electrons: negligible shielding (same shell)
Total shielding ...
Q4: Define electron affinity. Explain why noble gases have very low (or near zero) electron affinity.
Electron Affinity Definition:
Electron affinity (EA) is the amount of energy released when a neutral, gaseous atom gains one mole of electrons to form a negative ion.
X(g) + e⁻ → X⁻(g) + ΔE
Units: kJ/mol or eV
More negative EA = greater tendency to gain electrons
Trend in Periodic Table:
→ Generally increases across a period (left to right)
→ Generally decreases down a group
→ Halogens have highest electron affinity
→ Noble gases have nearly zero electron affinity
Why Noble Gases Have Very...
Q5: What is electronegativity? Explain the Pauling scale and trends in electronegativity across the periodic table.
Electronegativity Definition:
Electronegativity is the relative tendency of an atom to attract the electron pair towards itself in a covalent bond.
It is a measure of the ability of an atom to pull electron density in a chemical bond.
Note: Electronegativity ≠ Electron affinity
→ Electronegativity: applies to bonded atoms
→ Electron affinity: applies to isolated atoms gaining electrons
Pauling Scale:
Linus Pauling developed a relative scale (0 to 4) to express electronegativity.
Scales:
→ F...
Q6: Predict whether the following compounds are ionic or covalent based on electronegativity difference. (a) NaCl, (b) HCl, (c) Cl2, (d) MgO
Criterion for Bond Type (Pauling Scale):
Δ EN = |EN(atom 1) - EN(atom 2)|
Classification:
→ Δ EN ≥ 1.7 → Ionic bond
→ 0.4 < Δ EN < 1.7 → Polar covalent bond
→ Δ EN ≤ 0.4 → Nonpolar covalent bond
Electronegativity Values:
Na = 0.93, Cl = 3.16, H = 2.20, Mg = 1.31, O = 3.44
(a) NaCl:
Δ EN = |0.93 - 3.16| = 2.23
Since Δ EN = 2.23 > 1.7
Bond Type: IONIC
NaCl is an ionic compound (metal + nonmetal)
(b) HCl:
Δ EN = |2.20 - 3.16| = 0.96
Since 0.4 < Δ EN (0.96) < 1.7
Bond Type: POLA...
Showing 6 of 7 questions. Visit the full page for complete solutions.
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