Chemistry
Chapter 1
Board Weightage: 10 - 12 Marks in ICSE Board Exam
Periodic Properties & Variations
Prescribed Textbook: Selina Concise Chemistry (Class 10) - Dr. S.P. Singh
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🔑 Mandatory ICSE Examiner Technical Keywords with Detailed Description
Official CISCE Evaluation Benchmark
According to CISCE board marking schemes, evaluators allocate marks based on the explicit presence of mandatory technical keywords. General or colloquial explanations fail to secure full marks. The table below details every required technical term, its scientific/academic description, the evaluator directive, and its exact model answer usage.
Mandatory Keyword #1
Core Definition
Chapter Concept: Modern Periodic Law
1 Mark in Chemical Observation / Balanced Equation
"Periodic functions"
📘 Technical Definition & Detailed Description:
In ICSE Class 10 Chemistry (Periodic Properties & Variations), "Periodic functions" denotes a critical reaction condition, bonding mechanism, stoichiometric rule, or analytical observation required by CISCE.
Examiners award marks specifically when "Periodic functions" is included alongside balanced chemical equations, observable color changes, or state symbols (s, l, g, aq).
📝 Model Answer Application (Exact Phrasing for Board Exam):
"During the reaction in Modern Periodic Law, ensure "Periodic functions" is explicitly stated in the balanced explanation."
Mandatory Keyword #2
Core Definition
Chapter Concept: Modern Periodic Law
1 Mark in Chemical Observation / Balanced Equation
"Atomic numbers"
📘 Technical Definition & Detailed Description:
In ICSE Class 10 Chemistry (Periodic Properties & Variations), "Atomic numbers" denotes a critical reaction condition, bonding mechanism, stoichiometric rule, or analytical observation required by CISCE.
Examiners award marks specifically when "Atomic numbers" is included alongside balanced chemical equations, observable color changes, or state symbols (s, l, g, aq).
📝 Model Answer Application (Exact Phrasing for Board Exam):
"During the reaction in Modern Periodic Law, ensure "Atomic numbers" is explicitly stated in the balanced explanation."
Mandatory Keyword #3
Core Definition
Chapter Concept: Modern Periodic Law
1 Mark in Chemical Observation / Balanced Equation
"Not atomic mass"
📘 Technical Definition & Detailed Description:
In ICSE Class 10 Chemistry (Periodic Properties & Variations), "Not atomic mass" denotes a critical reaction condition, bonding mechanism, stoichiometric rule, or analytical observation required by CISCE.
Examiners award marks specifically when "Not atomic mass" is included alongside balanced chemical equations, observable color changes, or state symbols (s, l, g, aq).
📝 Model Answer Application (Exact Phrasing for Board Exam):
"During the reaction in Modern Periodic Law, ensure "Not atomic mass" is explicitly stated in the balanced explanation."
Mandatory Keyword #4
Core Definition
Chapter Concept: Ionisation Potential (I.P.)
1 Mark in Chemical Observation / Balanced Equation
"Energy required"
📘 Technical Definition & Detailed Description:
In ICSE Class 10 Chemistry (Periodic Properties & Variations), "Energy required" denotes a critical reaction condition, bonding mechanism, stoichiometric rule, or analytical observation required by CISCE.
Examiners award marks specifically when "Energy required" is included alongside balanced chemical equations, observable color changes, or state symbols (s, l, g, aq).
📝 Model Answer Application (Exact Phrasing for Board Exam):
"During the reaction in Ionisation Potential (I.P.), ensure "Energy required" is explicitly stated in the balanced explanation."
Mandatory Keyword #5
Core Definition
Chapter Concept: Ionisation Potential (I.P.)
1 Mark in Chemical Observation / Balanced Equation
"Most loosely bound electron"
📘 Technical Definition & Detailed Description:
In ICSE Class 10 Chemistry (Periodic Properties & Variations), "Most loosely bound electron" denotes a critical reaction condition, bonding mechanism, stoichiometric rule, or analytical observation required by CISCE.
Examiners award marks specifically when "Most loosely bound electron" is included alongside balanced chemical equations, observable color changes, or state symbols (s, l, g, aq).
📝 Model Answer Application (Exact Phrasing for Board Exam):
"During the reaction in Ionisation Potential (I.P.), ensure "Most loosely bound electron" is explicitly stated in the balanced explanation."
Mandatory Keyword #6
Core Definition
Chapter Concept: Ionisation Potential (I.P.)
1 Mark in Chemical Observation / Balanced Equation
"Isolated gaseous atom"
📘 Technical Definition & Detailed Description:
In ICSE Class 10 Chemistry (Periodic Properties & Variations), "Isolated gaseous atom" denotes a critical reaction condition, bonding mechanism, stoichiometric rule, or analytical observation required by CISCE.
Examiners award marks specifically when "Isolated gaseous atom" is included alongside balanced chemical equations, observable color changes, or state symbols (s, l, g, aq).
📝 Model Answer Application (Exact Phrasing for Board Exam):
"During the reaction in Ionisation Potential (I.P.), ensure "Isolated gaseous atom" is explicitly stated in the balanced explanation."
Mandatory Keyword #7
Core Definition
Chapter Concept: Ionisation Potential (I.P.)
1 Mark in Chemical Observation / Balanced Equation
"Units: kJ/mol or eV"
📘 Technical Definition & Detailed Description:
In ICSE Class 10 Chemistry (Periodic Properties & Variations), "Units: kJ/mol or eV" denotes a critical reaction condition, bonding mechanism, stoichiometric rule, or analytical observation required by CISCE.
Examiners award marks specifically when "Units: kJ/mol or eV" is included alongside balanced chemical equations, observable color changes, or state symbols (s, l, g, aq).
📝 Model Answer Application (Exact Phrasing for Board Exam):
"During the reaction in Ionisation Potential (I.P.), ensure "Units: kJ/mol or eV" is explicitly stated in the balanced explanation."
Mandatory Keyword #8
Core Definition
Chapter Concept: Electronegativity (E.N.)
1 Mark in Chemical Observation / Balanced Equation
"Atom in a molecule"
📘 Technical Definition & Detailed Description:
In ICSE Class 10 Chemistry (Periodic Properties & Variations), "Atom in a molecule" denotes a critical reaction condition, bonding mechanism, stoichiometric rule, or analytical observation required by CISCE.
Examiners award marks specifically when "Atom in a molecule" is included alongside balanced chemical equations, observable color changes, or state symbols (s, l, g, aq).
📝 Model Answer Application (Exact Phrasing for Board Exam):
"During the reaction in Electronegativity (E.N.), ensure "Atom in a molecule" is explicitly stated in the balanced explanation."
Mandatory Keyword #9
Core Definition
Chapter Concept: Electronegativity (E.N.)
1 Mark in Chemical Observation / Balanced Equation
"Attract shared pair of electrons"
📘 Technical Definition & Detailed Description:
In ICSE Class 10 Chemistry (Periodic Properties & Variations), "Attract shared pair of electrons" denotes a critical reaction condition, bonding mechanism, stoichiometric rule, or analytical observation required by CISCE.
Examiners award marks specifically when "Attract shared pair of electrons" is included alongside balanced chemical equations, observable color changes, or state symbols (s, l, g, aq).
📝 Model Answer Application (Exact Phrasing for Board Exam):
"During the reaction in Electronegativity (E.N.), ensure "Attract shared pair of electrons" is explicitly stated in the balanced explanation."
Mandatory Keyword #10
Core Definition
Chapter Concept: Electronegativity (E.N.)
1 Mark in Chemical Observation / Balanced Equation
"Fluorine is highest (4.0)"
📘 Technical Definition & Detailed Description:
In ICSE Class 10 Chemistry (Periodic Properties & Variations), "Fluorine is highest (4.0)" denotes a critical reaction condition, bonding mechanism, stoichiometric rule, or analytical observation required by CISCE.
Examiners award marks specifically when "Fluorine is highest (4.0)" is included alongside balanced chemical equations, observable color changes, or state symbols (s, l, g, aq).
📝 Model Answer Application (Exact Phrasing for Board Exam):
"During the reaction in Electronegativity (E.N.), ensure "Fluorine is highest (4.0)" is explicitly stated in the balanced explanation."
Complete step-by-step evaluator solutions for textbook problems and 5 generated practice sets adhering to CISCE marking schemes.
📘 Textbook Problem: Selina Chapter 1 - Review Question 15
Selina Concise Chemistry Class 10
4 Marks Total
Account for the following: (a) Ionisation potential increases across a period from left to right. (b) Atomic size decreases across a period.
Step-by-Step Marking Breakdown
Part (a) Ionisation Potential Trend: Across a period from left to right, the atomic number (nuclear charge) increases while the number of shells remains constant. Consequently, the effective nuclear pull on valence electrons increases, making it harder to remove an electron. Thus, I.P. increases.
2 Marks
Part (b) Atomic Size Trend: As nuclear charge increases across the period with no addition of extra shells, the outer electrons are pulled closer to the nucleus. Hence, atomic radius decreases.
2 Marks
Final Answer: Both trends stem from increased effective nuclear charge with constant number of electron shells.
(Units: kJ/mol, pm)
💡 Examiner Tip: Always mention TWO factors in periodic trend reasoning: (1) Nuclear charge, and (2) Number of electron shells / shielding effect.
🎯 Generated Set: Generated Practice Set 1 - Core Concept (2 Marks)
ICSE Class 10 Exam Blueprint - Chapter 1
2 Marks Total
Define "Modern Periodic Law" in the context of ICSE Class 10 Chemistry. State its primary characteristic or SI unit/standard symbol.
Step-by-Step Marking Breakdown
Step 1: Precise Technical Definition: The physical and chemical properties of elements are periodic functions of their atomic numbers (Moseley).
1 Mark
Step 2: Mandatory Technical Criteria: Ensure the definition contains mandatory keywords: Periodic functions, Atomic numbers, Not atomic mass.
1 Mark
Final Answer: Accurate scientific/scholarly definition containing all mandatory ICSE evaluation keywords.
(Units: Elementary charge)
💡 Examiner Tip: Avoid colloquial explanations. Use the exact technical definition given in prescribed CISCE curriculum.
🎯 Generated Set: Generated Practice Set 2 - Method & Application (3 Marks)
ICSE Question Bank & Specimen Framework - Chemistry
3 Marks Total
A system governed by "Periodic Trend Across a Period (Left to Right)" has standard parameters. Using the relation Nuclear Charge ↑ | Atomic Radius ↓ | I.P. ↑ | E.A. ↑ | E.N. ↑ | Non-metallic Character ↑, calculate the required variable when other quantities are doubled. State the formula and show step-by-step substitution.
Step-by-Step Marking Breakdown
Step 1: State the Formula / Conceptual Principle: Write the primary governing equation: Nuclear Charge ↑ | Atomic Radius ↓ | I.P. ↑ | E.A. ↑ | E.N. ↑ | Non-metallic Character ↑. Define each symbol clearly.
Formula: Nuclear Charge ↑ | Atomic Radius ↓ | I.P. ↑ | E.A. ↑ | E.N. ↑ | Non-metallic Character ↑
1 Mark
Step 2: Mathematical / Procedural Deduction: Substitute the modified parameters: Let initial state be S₁ and new state be S₂. Set up the ratio S₂ / S₁ and simplify algebraically.
1 Mark
Step 3: Concluding Result & Interpretation: Express the final outcome clearly with proper units or scientific deduction.
1 Mark
Final Answer: Result derived directly from Nuclear Charge ↑ | Atomic Radius ↓ | I.P. ↑ | E.A. ↑ | E.N. ↑ | Non-metallic Character ↑
(Units: Elementary charge)
💡 Examiner Tip: In derivation and numerical questions, every intermediate mathematical step carries fractional credit.
🎯 Generated Set: Generated Practice Set 3 - Comparative Analysis (3 Marks)
ICSE Exemplar Practice Paper - Chemistry
3 Marks Total
Differentiate between "Modern Periodic Law" and "Ionisation Potential (I.P.)" on the basis of: (i) Fundamental definition/mechanism, (ii) Key working condition or formula, (iii) Real-world practical example or application.
Step-by-Step Marking Breakdown
Point 1: Conceptual Difference: Contrast the primary mechanisms: Modern Periodic Law focuses on Periodic functions, whereas Ionisation Potential (I.P.) emphasizes Energy required.
1 Mark
Point 2: Quantitative / Operational Difference: Highlight differences in formulas, governing laws, operating environments, or physical behavior.
1 Mark
Point 3: Exemplary Differentiation: Provide one clear, unambiguous textbook example illustrating each concept under everyday conditions.
1 Mark
Final Answer: Three-point structured comparative table with clear opposing criteria.
(Units: Tabular points)
💡 Examiner Tip: Always construct a comparative answer in a two-column table with an explicit "Point of Difference" header column.
🎯 Generated Set: Generated Practice Set 4 - Board Standard Structured (4 Marks)
ICSE Board Marking Blueprint - Class 10
4 Marks Total
A comprehensive ICSE examination question based on "Periodic Properties & Variations":
(i) State the fundamental law or rule governing "Modern Periodic Law". [1 Mark]
(ii) How does this concept change with temperature / pressure / time / scale? [1 Mark]
(iii) State one common mistake students make in this chapter and provide the correct scientific reasoning. [2 Marks]
Step-by-Step Marking Breakdown
Part (i): Statement of the Law: State the formal principle verbatim as recognized by CISCE syllabus committees.
1 Mark
Part (ii): Dependency Analysis: Explain the direct or inverse variation of the target variable with respect to environmental or operational factors.
1 Mark
Part (iii): Error Analysis & Correct Resolution: Identify the frequent pitfall: Students often confuse Periodic functions with related quantities. The correct understanding requires strict application of Electronegativity (E.N.).
2 Marks
Final Answer: Structured 4-mark solution completely addressing parts (i), (ii), and (iii).
(Units: Multi-part breakdown)
💡 Examiner Tip: Notice the mark distribution in multi-part questions; allocate your answering time and detail strictly in proportion to allotted marks.
🎯 Generated Set: Generated Practice Set 5 - Higher Order Thinking (HOTS) (4 Marks)
ICSE High-Achiever Challenge Series - Class 10
4 Marks Total
A critical scenario-based problem in "Periodic Properties & Variations": An experiment is performed under non-ideal conditions involving "Modern Periodic Law" and "Ionisation Potential (I.P.)".
(a) Predict what happens to the expected outcome if the boundary condition fails.
(b) Give complete scientific justification.
(c) State the critical safeguard or correction formula to rectify the error.
Step-by-Step Marking Breakdown
Part (a): Prediction of Anomalous Outcome: Accurately predict the deviation from theoretical expectations when standard assumptions are violated.
1 Mark
Part (b): Scientific Justification: Provide a rigorous scientific explanation using first principles and mandatory keywords: Periodic functions, Atomic numbers, Not atomic mass, Energy required.
2 Marks
Part (c): Correction Protocol & Mathematical Remedy: State the exact rectification formula or procedural calibration necessary to restore accuracy.
Formula: Nuclear Charge ↑ | Atomic Radius ↓ | I.P. ↑ | E.A. ↑ | E.N. ↑ | Non-metallic Character ↑
1 Mark
Final Answer: Full scenario analysis with anomaly prediction, first-principles justification, and correction method.
(Units: HOTS Analytical Reasoning)
💡 Examiner Tip: HOTS questions in ICSE evaluate depth of conceptual understanding. Avoid superficial guessing; reason backward from core laws.