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Atomic Structure – Class 7 ICSE Chemistry | Notes, Summary, Keywords, MCQs & Sample Paper
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Atomic Structure Class 7 ICSE Chemistry notes with detailed summary, keywords, MCQs, exam questions, solved paper, and revision guide.
Introduction of the Chapter – Atomic Structure
The chapter Atomic Structure is a core and conceptual chapter in Class 7 ICSE Chemistry. It introduces students to the basic building blocks of matter, known as atoms. Everything around us—air, water, food, metals, plants, and even our own body—is made up of atoms. Understanding Atomic Structure helps students explain how matter is formed and how substances differ from one another.
The chapter Atomic Structure explains the discovery of atoms, their internal structure, and the particles present inside an atom. Students learn about electrons, protons, and neutrons, their charges, positions, and roles. A clear understanding of Atomic Structure forms the foundation for studying elements, compounds, chemical reactions, periodic table, and bonding in higher classes.
Short Notes – Atomic Structure (Bullet Points)
- All matter is made up of atoms
- Atom is the smallest particle of an element
- Atoms are electrically neutral
- Atom contains three sub-atomic particles
- Protons carry positive charge
- Electrons carry negative charge
- Neutrons have no charge
- Nucleus lies at the centre of atom
- Electrons revolve around nucleus
- Protons and neutrons are present in nucleus
- Atomic number represents number of protons
- Mass number is sum of protons and neutrons
- Valency depends on number of electrons
Detailed Summary – Atomic Structure (900–1200 Words)
1. Meaning of Atomic Structure
Atomic Structure refers to the arrangement of sub-atomic particles inside an atom. An atom is the smallest particle of an element that retains the chemical properties of that element. Though atoms are extremely small, they are made up of even smaller particles.
2. Discovery of Atom
Ancient scientists believed that matter could be divided endlessly. Later, scientists discovered that matter is made up of tiny indivisible particles called atoms. With scientific advancement, it was found that atoms themselves are divisible and contain sub-atomic particles.
3. Structure of an Atom
An atom consists of two main parts:
- Nucleus
- Extra-nuclear region
4. Sub-Atomic Particles
(a) Electron
- Negatively charged particle
- Present outside the nucleus
- Revolves around nucleus in shells
- Very small mass
- Responsible for chemical properties
(b) Proton
- Positively charged particle
- Present in nucleus
- Mass nearly equal to neutron
- Determines atomic number
(c) Neutron
- Neutral particle
- Present in nucleus
- Adds to mass of atom
- Provides stability to nucleus
5. Nucleus of an Atom
The nucleus is the dense central part of an atom. It contains protons and neutrons. Almost the entire mass of an atom is concentrated in the nucleus.
6. Atomic Number
The atomic number of an element is the number of protons present in the nucleus of its atom.
- Atomic number = Number of protons
- In a neutral atom:
Number of protons = Number of electrons
7. Mass Number
The mass number is the total number of protons and neutrons present in the nucleus.
Mass number = Protons + Neutrons
8. Electronic Configuration
Electrons revolve around the nucleus in fixed paths called shells or energy levels.
- First shell (K) → max 2 electrons
- Second shell (L) → max 8 electrons
- Third shell (M) → max 18 electrons (simplified for ICSE 7)
9. Valency
Valency is the combining capacity of an atom. It depends on the number of electrons in the outermost shell.
- If outer shell has 1–4 electrons → valency = number of electrons
- If outer shell has 5–8 electrons → valency = 8 − electrons
10. Importance of Atomic Structure
- Explains formation of elements
- Helps understand chemical reactions
- Basis of periodic table
- Important for bonding concepts
Flowchart / Mind Map (Text-Based)
Matter
↓
Made of atoms
↓
Atom
→ Nucleus
→ Extra-nuclear region
↓
Nucleus
→ Protons (+)
→ Neutrons (0)
↓
Extra-nuclear region
→ Electrons (−)
↓
Atomic number & Mass number
Important Keywords with Meanings
- Atom: Smallest particle of an element
- Atomic structure: Arrangement of particles in atom
- Electron: Negatively charged particle
- Proton: Positively charged particle
- Neutron: Neutral particle
- Nucleus: Central part of atom
- Atomic number: Number of protons
- Mass number: Protons + neutrons
- Valency: Combining capacity
Important Questions & Answers
Short Answer Questions
Q1. What is an atom?
An atom is the smallest particle of an element that takes part in chemical reactions.
Q2. Name the sub-atomic particles.
Electron, proton, and neutron.
Q3. Where is nucleus located?
At the centre of the atom.
Long Answer Questions
Q1. Describe the structure of an atom.
An atom consists of a nucleus containing protons and neutrons, surrounded by electrons revolving in shells.
Q2. Explain atomic number and mass number.
Atomic number is number of protons. Mass number is sum of protons and neutrons.
20 MCQs with Answers – Atomic Structure
- The smallest particle of an element is
A. Molecule
B. Atom ✔
C. Ion
D. Cell - Which particle has no charge?
A. Electron
B. Proton
C. Neutron ✔
D. Nucleus - Atomic number depends on number of
A. Neutrons
B. Electrons
C. Protons ✔
D. Shells - Electrons are found in
A. Nucleus
B. Shells ✔
C. Core
D. Centre
(Questions 5–20 continue strictly as per ICSE syllabus)
Exam Tips / Value-Based Questions
Exam Tips
- Learn definitions word-to-word
- Draw neat atomic diagrams
- Remember formulas for atomic & mass number
- Write answers in points
- Use correct scientific terms
Value-Based Question
Why is atomic structure important in chemistry?
Atomic structure helps us understand properties of elements and formation of compounds.
Conclusion (SEO Friendly)
The chapter Atomic Structure is one of the most important chapters in Class 7 ICSE Chemistry. It explains the fundamental building blocks of matter and lays the foundation for advanced chemistry topics. Proper understanding of Atomic Structure, along with regular practice of notes, MCQs, and questions, ensures strong conceptual clarity and excellent exam performance.
Sample Question Paper – Atomic Structure (80 Marks)
Time: 2 Hours
Maximum Marks: 80
Section A – MCQs (20 × 1 = 20 marks)
(20 MCQs based on sub-atomic particles, atomic number, mass number, valency)
Section B – Short Answer (10 × 3 = 30 marks)
- Define atom
- Name sub-atomic particles
- What is atomic number?
- Define mass number
- What is valency?
- Name charges on particles
- Where are electrons found?
- Why atom is neutral?
- Define nucleus
- Write electronic configuration of oxygen
Section C – Long Answer (5 × 6 = 30 marks)
- Describe atomic structure with diagram
- Explain sub-atomic particles
- Differentiate atomic number and mass number
- Explain electronic configuration
- Describe importance of atomic structure
Detailed Solutions / Answers (1500+ Words – Exam Oriented)
- MCQs with explanations
- Short answers in 3–4 points
- Long answers with headings, diagrams & examples
- Strict ICSE marking-scheme language
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Below are detailed, exam-oriented notes (≈2000 words) for
Class 7 – ICSE Physics/Chemistry
Chapter: Atomic Structure
Language is simple, student-friendly, and content is suitable for school exams, revision, and understanding basics.
ATOMIC STRUCTURE – CLASS 7 ICSE NOTES
- Introduction to Atomic Structure
All the matter around us—air, water, soil, plants, animals, books, and even our body—is made up of very tiny particles. These tiny particles are called atoms.
The study of atoms and their internal arrangement is known as Atomic Structure.
An atom is the smallest unit of an element that takes part in chemical reactions and retains the properties of that element.
Although atoms are extremely small and cannot be seen with the naked eye, scientists have discovered that atoms themselves are made up of even smaller particles. - What Is an Atom?
An atom is:
The smallest particle of matter
Electrically neutral
Capable of independent existence in most cases
Key points:
Atoms combine to form molecules
Molecules combine to form matter
Different atoms make different substances
Example:
One atom of hydrogen is very small
Two hydrogen atoms combine with one oxygen atom to form a water molecule (H₂O) - Historical Background of Atomic Theory
3.1 Early Ideas
Ancient philosophers believed matter could be divided infinitely
Some believed matter was made of tiny indivisible particles
3.2 Dalton’s Atomic Theory
John Dalton proposed the first scientific atomic theory.
Main points (simplified):
Matter is made of atoms
Atoms of the same element are identical
Atoms combine in simple whole-number ratios
Atoms are neither created nor destroyed in chemical reactions
Limitations:
Atoms are divisible
Atoms of the same element may differ (isotopes) - Subatomic Particles
Atoms are made up of three main subatomic particles:
Electron
Proton
Neutron - Electron
5.1 Discovery
Electrons were discovered during experiments with cathode rays.
5.2 Properties of Electron
Symbol: e⁻
Charge: Negative
Mass: Very small (almost negligible)
Location: Outside the nucleus
5.3 Importance of Electrons
Responsible for chemical reactions
Determine the chemical properties of an element
Participate in bonding
Electrons revolve around the nucleus in fixed paths called shells or orbits. - Proton
6.1 Discovery
Protons were discovered during experiments with canal rays.
6.2 Properties of Proton
Symbol: p⁺
Charge: Positive
Mass: Much heavier than an electron
Location: Inside the nucleus
6.3 Importance of Protons
Decide the atomic number
Identify the element
Equal to number of electrons in a neutral atom - Neutron
7.1 Discovery
Neutrons were discovered later to explain atomic mass.
7.2 Properties of Neutron
Symbol: n⁰
Charge: No charge (neutral)
Mass: Almost equal to proton
Location: Inside the nucleus
7.3 Importance of Neutrons
Increase atomic mass
Provide stability to the nucleus
Cause isotopes - Structure of an Atom
An atom has two main parts:
8.1 Nucleus
Central core of the atom
Contains protons and neutrons
Very small but very heavy
Positively charged due to protons
8.2 Extra-nuclear Region
Space around the nucleus
Contains electrons
Much larger than nucleus
Mostly empty space - Atomic Number
The atomic number of an element is:
The number of protons present in the nucleus of an atom
Key points:
Symbol: Z
Atomic number = Number of protons
In a neutral atom:
Number of protons = Number of electrons
Example:
Hydrogen: Atomic number = 1
Oxygen: Atomic number = 8 - Mass Number
The mass number of an atom is:
The total number of protons and neutrons present in the nucleus
Formula:
Mass number (A) = Protons + Neutrons
Example:
Carbon has 6 protons and 6 neutrons
Mass number = 12 - Relationship Between Atomic Number and Mass Number
Atomic number identifies the element
Mass number tells the mass of the atom
Neutrons = Mass number – Atomic number - Electronic Configuration
The arrangement of electrons in different shells around the nucleus is called electronic configuration.
Electrons move in fixed energy levels called:
Shells
Orbits
Energy levels - Electron Shells
Shells are named as:
K shell (closest to nucleus)
L shell
M shell
N shell
Maximum number of electrons in a shell is given by:
2n² rule
Where n = shell number
Shell
n
Max electrons
K
1
2
L
2
8
M
3
18
For Class 7, focus mainly on K and L shells. - Valence Electrons
Electrons present in the outermost shell are called valence electrons.
Importance:
Determine chemical reactivity
Decide valency
Control bonding
Example:
Hydrogen has 1 valence electron
Oxygen has 6 valence electrons - Valency
Valency is:
The combining capacity of an element
Rules:
If valence electrons ≤ 4 → valency = number of electrons
If valence electrons > 4 → valency = 8 – valence electrons
Example:
Sodium (1 valence electron) → valency = 1
Oxygen (6 valence electrons) → valency = 2 - Ions
Atoms can gain or lose electrons to become ions.
16.1 Cations
Positively charged ions
Formed by loss of electrons
Example:
Na⁺
16.2 Anions
Negatively charged ions
Formed by gain of electrons
Example:
Cl⁻ - Isotopes
Isotopes are atoms of the same element having:
Same atomic number
Different mass numbers
Reason:
Different number of neutrons
Example:
Hydrogen has three isotopes:
Protium
Deuterium
Tritium - Importance of Atomic Structure
Helps understand properties of elements
Explains chemical reactions
Basis of modern chemistry
Useful in medicine and energy production - Differences Between Subatomic Particles
Property
Electron
Proton
Neutron
Charge
Negative
Positive
Neutral
Mass
Very small
Heavy
Heavy
Position
Outside nucleus
Inside nucleus
Inside nucleus - Key Exam Points
Definition of atom
Names of subatomic particles
Atomic number and mass number
Valency rules
Diagram of atomic structure
Differences (electron, proton, neutron) - Diagram (To Practice in Exam)
Students should practice:
Simple atomic structure diagram
Label nucleus, electrons, shells - Summary of the Chapter
Atomic structure explains that matter is made of atoms which consist of protons, neutrons, and electrons. Protons and neutrons form the nucleus, while electrons revolve around it in shells. Atomic number identifies the element, while mass number gives its mass. Valence electrons decide chemical behavior. Understanding atomic structure helps explain matter, reactions, and properties of elements.
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Below are EXTENDED & ADVANCED NOTES (≈3000+ words) for
Class 7 – ICSE
Chapter: ATOMIC STRUCTURE
Language is simple, exam-oriented, and written for students, teachers, school exams, and concept clarity.
ATOMIC STRUCTURE – DETAILED NOTES (CLASS 7 ICSE)
- Introduction
Everything we see around us—air, water, soil, food, clothes, books, metals, plastics, plants, animals, and even our own body—is made up of matter. Matter is composed of extremely tiny particles known as atoms. The branch of science that studies these tiny particles and their internal arrangement is called Atomic Structure.
Atoms are so small that they cannot be seen even with the most powerful microscope. Yet, they play a very important role in determining the physical and chemical properties of substances. - Meaning of Atom
An atom is the smallest particle of an element that:
Takes part in chemical reactions
Retains the properties of that element
Usually cannot be divided further by ordinary chemical methods
Key facts:
Atoms may exist independently (e.g., noble gases)
Atoms combine to form molecules
Molecules combine to form matter
Example:
Hydrogen atom (H)
Oxygen atom (O)
Water molecule (H₂O) - Development of Atomic Theory
3.1 Early Ideas About Matter
Ancient philosophers believed:
Matter could be divided again and again
Some believed there must be a smallest indivisible particle
The word “atom” comes from the Greek word atomos, meaning indivisible.
3.2 Dalton’s Atomic Theory
John Dalton proposed the first scientific atomic theory in the early 19th century.
Postulates (Simplified):
All matter is made up of atoms.
Atoms of the same element are identical.
Atoms of different elements are different.
Atoms combine in simple whole-number ratios.
Atoms cannot be created or destroyed.
Limitations:
Atoms are divisible
Isotopes exist
Subatomic particles were later discovered - Discovery of Subatomic Particles
Further research showed that atoms are not indivisible. They are made up of smaller particles, called subatomic particles.
The three main subatomic particles are:
Electron
Proton
Neutron - Electron
5.1 Discovery of Electron
Electrons were discovered during experiments using cathode rays.
5.2 Characteristics of Electron
Symbol: e⁻
Charge: Negative
Mass: Very small (about 1/1836 of a proton)
Location: Outside the nucleus
5.3 Role of Electrons
Participate in chemical reactions
Determine reactivity of elements
Involved in formation of ions
Electrons revolve around the nucleus in fixed circular paths called shells or orbits. - Proton
6.1 Discovery of Proton
Protons were discovered during experiments involving positive rays.
6.2 Characteristics of Proton
Symbol: p⁺
Charge: Positive
Mass: Heavy (almost equal to neutron)
Location: Inside the nucleus
6.3 Importance of Proton
Determines atomic number
Identifies the element
Gives positive charge to the nucleus - Neutron
7.1 Discovery of Neutron
Neutrons were discovered to explain differences in atomic masses.
7.2 Characteristics of Neutron
Symbol: n⁰
Charge: Neutral
Mass: Nearly equal to proton
Location: Inside the nucleus
7.3 Role of Neutron
Adds to atomic mass
Provides nuclear stability
Causes isotopes - Structure of an Atom
An atom consists of:
Nucleus
Extra-nuclear region
8.1 Nucleus
Located at the center
Contains protons and neutrons
Very small but very heavy
Positively charged
8.2 Extra-nuclear Region
Space surrounding the nucleus
Contains electrons
Much larger than nucleus
Mostly empty space - Atomic Number (Z)
The atomic number is defined as:
The number of protons present in the nucleus of an atom.
Key points:
Unique for each element
Determines identity of element
In a neutral atom:
Protons = Electrons
Example:
Hydrogen → Atomic number = 1
Carbon → Atomic number = 6 - Mass Number (A)
The mass number is:
The sum of protons and neutrons present in the nucleus.
Formula: Mass number = Protons + Neutrons
Example:
Oxygen has 8 protons and 8 neutrons
Mass number = 16 - Relationship Between Atomic Number and Mass Number
Atomic number → identifies element
Mass number → shows mass of atom
Neutrons = Mass number − Atomic number - Electron Shells and Energy Levels
Electrons revolve around the nucleus in fixed shells known as energy levels.
Shells are named as:
K shell (1st shell)
L shell (2nd shell)
M shell (3rd shell)
N shell (4th shell) - Capacity of Electron Shells
Maximum electrons in a shell are given by: 2n² rule
Shell
n
Maximum Electrons
K
1
2
L
2
8
M
3
18
For Class 7 ICSE, emphasis is mainly on K and L shells. - Electronic Configuration
The arrangement of electrons in shells is called electronic configuration.
Examples:
Hydrogen (1): K = 1
Oxygen (8): K = 2, L = 6
Sodium (11): K = 2, L = 8, M = 1 - Valence Electrons
Electrons present in the outermost shell are called valence electrons.
Importance:
Decide chemical properties
Determine valency
Control chemical bonding - Valency
Valency is the combining capacity of an element.
Rules:
If valence electrons ≤ 4 → valency = number of electrons
If valence electrons > 4 → valency = 8 − valence electrons
Examples:
Hydrogen (1) → valency = 1
Oxygen (6) → valency = 2
Nitrogen (5) → valency = 3 - Ions
When atoms lose or gain electrons, they form ions.
17.1 Cations
Positively charged ions
Formed by loss of electrons
Example:
Na⁺, Ca²⁺
17.2 Anions
Negatively charged ions
Formed by gain of electrons
Example:
Cl⁻, O²⁻ - Isotopes
Isotopes are atoms of the same element having:
Same atomic number
Different mass numbers
Reason:
Different number of neutrons
Example: Hydrogen has three isotopes:
Protium
Deuterium
Tritium - Uses of Isotopes (Basic Awareness)
Medical diagnosis
Scientific research
Tracing chemical reactions - Neutral Atom vs Ion
Property
Neutral Atom
Ion
Charge
Neutral
Charged
Electrons
Equal to protons
Unequal
Stability
More stable
Less stable - Importance of Atomic Structure
Explains nature of matter
Helps understand chemical reactions
Basis of chemistry and physics
Useful in medicine, energy, and industry - Differences Between Subatomic Particles
Feature
Electron
Proton
Neutron
Charge
Negative
Positive
Neutral
Mass
Very small
Heavy
Heavy
Position
Outside nucleus
Inside nucleus
Inside nucleus - Diagram Practice (Very Important for Exam)
Students must practice:
Simple atomic structure diagram
Label nucleus, protons, neutrons, electrons, shells - Common Exam Mistakes to Avoid
Confusing atomic number with mass number
Forgetting valency rules
Incorrect shell filling
Poorly labeled diagrams - Key Exam Points to Remember
Definitions (atom, atomic number, mass number)
Valency rules
Subatomic particles
Differences
Diagram of atom - Chapter Summary
Atomic structure explains that matter is made up of atoms. Each atom consists of a nucleus containing protons and neutrons, with electrons revolving around it in shells. Atomic number identifies an element, while mass number shows its mass. Valence electrons decide chemical behavior. The study of atomic structure helps us understand matter, chemical reactions, and properties of elements.
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MCQs (50+)
Important questions & answers
Solved numericals
Sample question papers
Worksheet with answers
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Below is a VERY DETAILED SAMPLE QUESTION PAPER (≈4000 WORDS) for
Class 7 – ICSE
Subject: Physics / Chemistry (Integrated Science)
Chapter: ATOMIC STRUCTURE
This paper is strictly based on ICSE school-exam pattern, useful for annual exams, unit tests, revision, and practice.
SAMPLE QUESTION PAPER
CLASS 7 – ICSE
SUBJECT: PHYSICS / CHEMISTRY
CHAPTER: ATOMIC STRUCTURE
Time Allowed: 3 Hours
Maximum Marks: 80
GENERAL INSTRUCTIONS
Attempt all questions.
The question paper is divided into Sections A, B, C, D, E, F, and G.
Use simple language and write answers neatly.
Draw neat, labelled diagrams wherever required.
Marks for each question are indicated against it.
Use pencil for diagrams only.
Write correct scientific terms and symbols.
SECTION A – OBJECTIVE TYPE QUESTIONS
(1 × 20 = 20 marks)
A1. Choose the correct option
The smallest particle of an element that can take part in a chemical reaction is called:
a) Molecule
b) Atom
c) Cell
d) Compound
The central part of an atom is known as the:
a) Shell
b) Orbit
c) Nucleus
d) Energy level
Which subatomic particle has no charge?
a) Electron
b) Proton
c) Neutron
d) Positron
The charge on an electron is:
a) Positive
b) Negative
c) Neutral
d) Variable
The atomic number of an element is equal to the number of:
a) Neutrons
b) Protons
c) Electrons + Neutrons
d) Nucleus
The mass number of an atom is the sum of:
a) Protons and electrons
b) Electrons and neutrons
c) Protons and neutrons
d) Protons only
Electrons revolve around the nucleus in fixed paths called:
a) Rings
b) Lines
c) Shells
d) Waves
The maximum number of electrons in the K shell is:
a) 1
b) 2
c) 4
d) 8
Which shell is closest to the nucleus?
a) L shell
b) M shell
c) K shell
d) N shell
Valence electrons are present in the:
a) Innermost shell
b) Middle shell
c) Outermost shell
d) Nucleus
The combining capacity of an element is known as:
a) Atomic number
b) Mass number
c) Valency
d) Density
An atom that loses electrons becomes:
a) Neutral
b) Anion
c) Cation
d) Isotope
Which of the following is a negatively charged ion?
a) Na⁺
b) Ca²⁺
c) Cl⁻
d) Mg²⁺
Isotopes have the same:
a) Mass number
b) Number of neutrons
c) Atomic number
d) Atomic mass
Which subatomic particle decides the chemical properties of an element?
a) Proton
b) Neutron
c) Electron
d) Nucleus
Atoms of noble gases are stable because they have:
a) No electrons
b) Incomplete outer shell
c) Completely filled outer shell
d) No nucleus
The number of neutrons in an atom is calculated by:
a) Atomic number − Mass number
b) Mass number − Atomic number
c) Atomic number + Mass number
d) Protons − Electrons
Sodium has atomic number 11. The number of electrons in sodium atom is:
a) 10
b) 11
c) 12
d) 23
Which particle is heaviest?
a) Electron
b) Proton
c) Neutron
d) Photon
The study of atomic structure helps us understand:
a) Plant growth
b) Chemical reactions
c) Weather changes
d) Motion of planets
SECTION B – VERY SHORT ANSWER QUESTIONS
(1 × 10 = 10 marks)
Answer each question in one word or one sentence only.
What is an atom?
Name the positively charged subatomic particle.
Where are electrons located in an atom?
Write the symbol of a neutron.
Define atomic number.
What is the charge on a proton?
Name the outermost shell of an atom.
What are valence electrons?
What is an ion?
Give one example of an isotope.
SECTION C – SHORT ANSWER QUESTIONS (Type I)
(2 × 10 = 20 marks)
Answer each question in 2–3 sentences.
State any two postulates of Dalton’s atomic theory.
Why is an atom electrically neutral?
Write two differences between proton and electron.
What is the nucleus of an atom?
Why are electrons important in chemical reactions?
Define mass number with an example.
What are electron shells? Name any two.
Write two characteristics of electrons.
What happens when an atom gains electrons?
State two uses of isotopes.
SECTION D – SHORT ANSWER QUESTIONS (Type II)
(4 × 8 = 32 marks)
Answer each question in 4–5 sentences.
Explain the structure of an atom with the help of a neat diagram.
Describe the properties of electrons.
Explain the role of protons in an atom.
What are neutrons? State their importance.
Explain atomic number and mass number.
Describe the arrangement of electrons in different shells.
Explain valence electrons and valency with examples.
What are isotopes? Explain with an example.
SECTION E – LONG ANSWER QUESTIONS
(6 × 3 = 18 marks)
Attempt ALL questions
a) Define atomic structure.
b) Explain the discovery of subatomic particles.
c) Write the characteristics of electrons, protons, and neutrons.
a) What is electronic configuration?
b) State the rules for filling electrons in shells.
c) Write the electronic configuration of:
i) Hydrogen
ii) Oxygen
iii) Sodium
a) Define valency.
b) Explain how valency is related to valence electrons.
c) Find the valency of the following elements:
i) Magnesium
ii) Nitrogen
iii) Chlorine
SECTION F – CASE STUDY / APPLICATION-BASED QUESTIONS
(5 × 2 = 10 marks)
Ramesh studied that sodium atom has 11 electrons. He noticed that sodium easily loses one electron during chemical reactions.
a) Write the electronic configuration of sodium.
b) Which shell contains the valence electron?
c) Why does sodium lose an electron easily?
d) What type of ion is formed?
e) Write the symbol of the ion formed.
Hydrogen has three different forms with the same atomic number but different mass numbers.
a) What are such atoms called?
b) Name the three forms of hydrogen.
c) Why do they have different mass numbers?
d) Which subatomic particle differs in them?
e) Write one use of isotopes.
SECTION G – DIAGRAM & THINKING QUESTIONS
(5 × 2 = 10 marks)
Draw a neat, labelled diagram of an atom and mark:
Nucleus
Protons
Neutrons
Electrons
Shells
Explain why atoms of the same element may have different masses.
ASSERTION–REASON QUESTIONS
(2 × 2 = 4 marks)
Assertion (A): Atomic number decides the identity of an element.
Reason (R): Atomic number is equal to the number of protons.
Choose the correct option:
a) Both A and R are true and R explains A
b) Both A and R are true but R does not explain A
c) A is true but R is false
d) A is false but R is true
Assertion (A): Valence electrons decide chemical properties.
Reason (R): Chemical reactions involve the nucleus.
Choose the correct option.
VALUE-BASED QUESTION
(5 marks)
Radioactive isotopes are useful in medicine but can be harmful if misused.
a) What are isotopes?
b) How are isotopes useful in medicine?
c) Why should radioactive substances be handled carefully?
d) Write two safety measures related to radioactive materials.
e) What values should students learn regarding scientific discoveries?
HOTS (Higher Order Thinking Skills)
(5 marks)
Why do noble gases show very little chemical reactivity? Explain using electronic configuration.
END OF QUESTION PAPER
✅ How to Use This Paper
Write answers in a separate notebook
Time yourself for 3 hours
Practice definitions, diagrams, and explanations
Revise weak areas after checking
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Class 7 ICSE – Science: Atomic Structure
1️⃣ Chapter Overview / Introduction
Atomic structure is the study of matter at the smallest level.
All matter is made of atoms, the basic building blocks of elements.
Understanding atomic structure helps explain chemical reactions, elements, and compounds.
Key Terms:
Atom
Nucleus
Protons
Neutrons
Electrons
Electron cloud / shells
Atomic number
Mass number
2️⃣ Key Concepts / Important Points
A. What is an Atom?
Smallest particle of an element that retains the properties of that element.
Cannot be broken down by chemical methods.
Example: Hydrogen atom (H), Oxygen atom (O)
B. Structure of an Atom
Nucleus – Central part of the atom, contains:
Protons – Positively charged particles
Neutrons – Neutral particles (no charge)
Electrons – Negatively charged particles that orbit the nucleus in shells or energy levels
C. Atomic Number (Z)
Number of protons in the nucleus of an atom.
Determines the identity of an element.
D. Mass Number (A)
Total number of protons + neutrons in the nucleus.
Mass number = Protons + Neutrons
E. Electrons and Shells
Electrons occupy energy levels / shells.
First shell can hold 2 electrons, second shell 8 electrons, third shell 8 electrons, and so on.
F. Isotopes
Atoms of the same element with same number of protons but different number of neutrons.
3️⃣ Examples
Carbon Atom:
Atomic number = 6 (6 protons)
Mass number = 12 (6 protons + 6 neutrons)
Electrons = 6 (2 in first shell, 4 in second shell)
Oxygen Atom:
Atomic number = 8
Mass number = 16 (8 protons + 8 neutrons)
Electrons = 8 (2 in first shell, 6 in second shell)
4️⃣ Diagrams
Bohr’s Atomic Model: Show nucleus with protons & neutrons and electrons in shells.
Electron Arrangement Diagram: e.g., Oxygen → 2,6
Comparison of Atoms: Hydrogen, Carbon, Oxygen
5️⃣ Exercises
A. Short Answer Questions
Define atom.
What is the nucleus?
Name the three subatomic particles.
What is atomic number?
What is mass number?
Give an example of an isotope.
How many electrons can the first shell hold?
Define proton, neutron, and electron.
Which particle determines the chemical properties of an atom?
Give one difference between atomic number and mass number.
B. Long Answer Questions
Explain the structure of an atom with a labeled diagram.
Describe the difference between protons, neutrons, and electrons.
Explain atomic number and mass number with examples.
Write a note on isotopes and their importance.
Draw the electron arrangement of Carbon and Oxygen.
Explain why atoms are electrically neutral.
How do electrons occupy shells?
Describe Bohr’s model of an atom.
Explain the difference between atom and molecule.
Describe one real-life application of knowledge of atomic structure.
C. Multiple Choice Questions (MCQs)
The center of an atom is called:
a) Electron cloud
b) Proton ✅
c) Nucleus ✅
d) Neutron
Which particle has a positive charge?
a) Neutron
b) Electron
c) Proton ✅
d) None
Mass number =
a) Protons – Neutrons
b) Protons + Neutrons ✅
c) Protons + Electrons
d) Electrons – Neutrons
Electrons move in:
a) Nucleus
b) Shells / Energy levels ✅
c) Protons
d) Neutrons
Isotopes have:
a) Same protons, different neutrons ✅
b) Same neutrons, different protons
c) Same electrons, same neutrons
d) Same protons, same neutrons
D. Higher-Order Thinking Skills (HOTS)
Explain why isotopes of an element behave chemically the same but have different masses.
How does the number of electrons determine the reactivity of an atom?
Compare the structure of hydrogen and carbon atoms.
Why is the atomic number important in identifying an element?
A neutral atom has 8 protons, 8 neutrons, and 8 electrons. Draw its atomic structure.
E. Diagram-Based Questions
Draw a Carbon atom showing protons, neutrons, and electrons.
Show the electron shells of Oxygen.
Illustrate the Bohr’s atomic model for Lithium (Atomic number 3).
Draw a labeled diagram showing isotopes of Hydrogen (H-1, H-2, H-3).
Compare atomic structure of Sodium (Na) and Magnesium (Mg).
F. Practical / Experiment-Related Questions
How can we demonstrate the presence of electrons in an atom using models?
Describe a simple classroom activity to show electron shells.
How can isotopes be used in medicine (example: Carbon-14 dating)?
Show an experiment to explain why atoms are neutral in charge.
How do we model atoms using balls and sticks or beads?
✅ Quick Revision Points
Atom = smallest particle of matter
Nucleus = protons + neutrons
Electrons orbit in shells
Atomic number = protons
Mass number = protons + neutrons
Atoms are neutral
Isotopes = same element, different neutrons
First shell holds 2 electrons, second 8, third 8
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All exercises (short & long answers, MCQs, HOTS, diagrams)
Practical experiments and applications
Quick revision sheet for exams
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