Matter Around Us — Exercise Solutions
Comprehensive solutions for TN State Board Class 7 Science Term 1 Chapter 3: Matter Around Us. Covers MCQs, fill in the blanks, true/false, match the following, analogy, assertion-reason, very short answers, short answers, detailed answers, and HOTS.
I. Choose the Appropriate Answer (MCQ)
Q1. Which of the following is an example of a metal?
(a) Iron ✓ (b) Oxygen (c) Helium (d) Water
Q2. Oxygen, hydrogen, and sulphur are examples of which of the following?
(a) Metals (b) Non-metals ✓ (c) Metalloids (d) Inert gases
Q3. Which of the following is a short and scientific way of representing one molecule of an element or compound?
(a) Mathematical formula (b) Chemical formula (c) Mathematical symbol (d) Chemical symbol ✓
Q4. The metal which is a liquid at room temperature:
(a) Chlorine (b) Sulphur (c) Mercury ✓ (d) Silver
Q5. An element which is always lustrous, malleable, and ductile:
(a) non-metal (b) metal ✓ (c) Metalloid (d) gas
Additional MCQs
Q6 (Additional). The graphite refill used in pencil is made of the element called ____
(a) graphite (b) carbon ✓ (c) silicon (d) sodium
Q7 (Additional). The smallest unit of an element is ____
(a) atom ✓ (b) molecule (c) compound (d) none
Q8 (Additional). The most abundant type of atom in the universe is ____
(a) Helium (b) Hydrogen ✓ (c) Argon (d) Oxygen
Q9 (Additional). ____ can be formed by the same or different kinds of atoms.
(a) Atom (b) Molecule ✓ (c) Gases (d) None
Q10 (Additional). ____ is a substance made up of three oxygen atoms chemically combined.
(a) Oxygen (b) Hydrogen (c) Ozone ✓ (d) CO₂
Q11 (Additional). A molecule containing three atoms is called a ____ molecule
(a) monoatomic (b) diatomic (c) triatomic ✓ (d) polyatomic
Q12 (Additional). A molecule which contains only one atom is called ____ molecule
(a) monoatomic ✓ (b) diatomic (c) triatomic (d) none
Q13 (Additional). An atom of oxygen (O) and two atoms of hydrogen (H₂) combine to form a molecule of ____
(a) hydrogen (b) ozone (c) water ✓ (d) none
Q14 (Additional). ____ is the first scientist who used the term element.
(a) Newton (b) Einstein (c) Robert Boyle ✓ (d) Robert Hooke
Q15 (Additional). Matter in its simplest form is called ____
(a) molecule (b) Metals (c) element ✓ (d) none
II. Fill in the Blanks
1. The smallest particle of matter that can exist by itself: atom. 2. A compound containing one atom of carbon and two atoms of oxygen is: CO₂. 3. ____ is the only non-metal that conducts electricity: Graphite. 4. Elements are made up of ____ kinds of atoms: same. 5. ____ of some elements are derived from Latin or Greek names of the elements: Symbol. 6. There are ____ number of known elements: 118. 7. Elements are the ____ form of pure substances: simplest. 8. The first letter of an element is always written in ____ letter: capital. 9. Molecules containing more than three atoms are known as: polyatomic molecule. 10. ____ is the most abundant gas in the atmosphere: Nitrogen.
Additional Fill in the Blanks
11. The name copper was taken from: cypress. 12. The first letter of a symbol is always written as a ____ letter and the second letter as a ____ letter: capital, small. 13. There are ____ hydrogen atoms in a water molecule: 2. 14. There is ____ oxygen atom in a water molecule: 1. 15. ____ is the total number of atoms present in one molecule of an element, compound, or a substance: Atomicity. 16. ____ is a mixture of gases: Air. 17. ____ is the life-giving element in the air: Oxygen. 18. During heating or expansion, the ____ of matter does not change: mass. 19. ____ is the smallest particle of an element: Atom. 20. ____ of an element consist of a fixed number of different types of atoms: Molecules.
III. Analogy Fill in the Blanks
1. Mercury : liquid at room temperature :: Oxygen : gas at room temperature 2. Non-metal conducting electricity : Graphite :: Metal conducting electricity : Copper 3. Elements : combine to form compounds :: Compounds : can be split into elements 4. Atoms : fundamental particle of an element :: Elements : fundamental particles of a compound
IV. True or False (with corrections)
Q1. Two different elements may have similar atoms.
True. Some different elements share similar atomic properties.
Q2. Compounds and elements are pure substances.
True. Both elements and compounds are pure substances with fixed compositions.
Q3. Atoms cannot exist alone; they can only exist as groups called molecules.
True. Most atoms combine to form molecules, though noble gases exist as single atoms.
Q4. NaCl represents one molecule of sodium chloride.
True. NaCl is the formula for one molecule of sodium chloride.
Q5. Argon is a monoatomic gas.
True. Argon (Ar) exists as individual atoms.
Additional True/False
Q6. Metals are usually solids or gases at room temperature.
False. Metals are usually solids at room temperature (except mercury which is liquid).
Q7. Non-metals are non-malleable.
True. Non-metals cannot be hammered into sheets; they are brittle.
Q8. Non-metals are usually good conductors of heat and electricity.
False. Metals are usually good conductors of heat and electricity. Non-metals are generally poor conductors (except graphite).
Q9. Sodium chloride is used as table salt and for flavoring and preserving food.
True. NaCl is common table salt.
Q10. Lead is also known as plumbum.
True. The Latin name for lead is plumbum, hence its symbol Pb.
V. Match the Following
Set 1:
| Answer | ||
|---|---|---|
| 1. CO₂ | (a) Robert Boyle | 1 → c (Triatomic molecule) |
| 2. Sulphur | (b) Making mobile phones | 2 → d (Polyatomic molecule) |
| 3. Element | (c) Triatomic molecule | 3 → a (Robert Boyle) |
| 4. Gallium | (d) Polyatomic molecule | 4 → b (Making mobile phones) |
Set 2:
| Answer | ||
|---|---|---|
| 1. Non-metals | (a) Silicon | 1 → c (dull and soft) |
| 2. Metals | (b) fire extinguisher | 2 → d (hard and shiny) |
| 3. Metalloids | (c) dull and soft | 3 → a (Silicon) |
| 4. Oxygen | (d) hard and shiny | 4 → e (supports fire) |
| 5. Water | (e) supports fire | 5 → b (fire extinguisher) |
VI. Very Short Answer Questions
Q1. How many elements are known at present?
118 elements.
Q2. Name the element used for making computer chips.
Silicon (Si).
Q3. Name the constituents of water.
Hydrogen (H) and Oxygen (O).
Q4. What is the expansion of IUPAC?
International Union of Pure and Applied Chemistry.
Q5. What is the Latin name of Sodium?
Natrium (Na).
Q6. What is a molecule?
A molecule is the smallest unit of a compound that retains its chemical properties. It is formed when two or more atoms combine chemically.
Q7. What is the fundamental particle of an element?
Atom.
Q8. What is a chemical formula?
A chemical formula is a symbolic representation of one molecule of an element or a compound. It shows the number and type of atoms present.
Additional Very Short Answers
Q9. What is an atom?
The smallest unit of an element that exhibits the properties of the element is called an atom.
Q10. What are the 3 most abundant atoms on Earth?
Iron, Oxygen, and Silicon.
Q11. Give two classifications of molecules.
1. A molecule containing only one atom is called a monoatomic molecule (e.g., noble gases). 2. A molecule containing two atoms is called a diatomic molecule (e.g., O₂, H₂).
Q12. Classify: (i) Silver (ii) Ammonia (iii) Water (iv) Mercury.
Silver — element; Ammonia — compound; Water — compound; Mercury — element.
Q13. Give an account of elements known to us.
There are 118 known elements. 94 occur naturally while 24 have been created artificially in the laboratory.
Q14. What are metalloids? Give examples.
Metalloids are elements with properties intermediate between metals and non-metals. Examples: Boron, Silicon, Germanium, Arsenic, Antimony.
Q15. Name a metal which (a) is liquid at room temperature (b) is the best conductor of heat.
(a) Mercury (b) Silver (also Copper)
VII. Short Answer Questions
Q1. Write the chemical formula and name the elements present in the following compounds:
| Compound | Formula | Elements Present |
|---|---|---|
| a. Sodium chloride | NaCl | Sodium (Na), Chlorine (Cl) |
| b. Potassium hydroxide | KOH | Potassium (K), Oxygen (O), Hydrogen (H) |
| c. Carbon dioxide | CO₂ | Carbon (C), Oxygen (O) |
| d. Calcium oxide | CaO | Calcium (Ca), Oxygen (O) |
| e. Sulphur dioxide | SO₂ | Sulphur (S), Oxygen (O) |
Q2. What do you understand by chemical formula of a compound? What is its significance?
A chemical formula is a symbolic representation of one molecule of an element or compound. Its significance: it tells us the elements present and the number of atoms of each element in one molecule of the substance.
Q3. Define the following terms with examples:
(a) Element: A substance that cannot be broken down into simpler substances by chemical means. Examples: Oxygen, Hydrogen, Gold, Helium.
(b) Compound: A pure substance formed when atoms of two or more elements combine chemically in definite proportions. Examples: H₂O, NaCl.
(c) Metal: A chemical element that is an effective conductor of electricity and heat, and is lustrous, malleable, and ductile. Examples: Copper, Iron, Silver.
(d) Non-metal: An element that is not lustrous, not malleable, and is a poor conductor of heat and electricity. Examples: Carbon, Iodine, Sulphur.
(e) Metalloid: An element exhibiting some properties of metals and some of non-metals; generally semiconductors. Examples: Silicon, Arsenic, Antimony, Boron.
Q4. Write the symbols for the following elements and classify them as solid, liquid, and gas:
| Element | Symbol | Classification |
|---|---|---|
| Aluminium | Al | Solid |
| Carbon | C | Solid |
| Chlorine | Cl | Gas |
| Mercury | Hg | Liquid |
| Hydrogen | H | Gas |
| Helium | He | Gas |
Q5. Classify the following as metals, non-metals, and metalloids: Sodium, Bismuth, Silver, Nitrogen, Silicon, Carbon, Chlorine, Iron, Copper.
| Category | Elements |
|---|---|
| Metal | Sodium, Bismuth, Silver, Iron, Copper |
| Non-metal | Nitrogen, Carbon, Chlorine |
| Metalloid | Silicon |
Q6. Classify the following as elements and compounds: Water, common salt, sugar, carbon dioxide, iodine, lithium.
| Category | Substances |
|---|---|
| Element | Iodine, Lithium |
| Compound | Water, Common salt, Sugar, Carbon dioxide |
Q7. Write the chemical formula for the following elements:
| Element | Formula |
|---|---|
| Hydrogen | H |
| Nitrogen | N |
| Ozone | O₃ |
| Sulphur | S |
Q8. What are elements? What are they made of? Give two examples.
Elements are chemically the simplest substances and cannot be broken down using chemical reactions. They are made entirely from one type of atom. Examples: Hydrogen, Oxygen.
Q9. Define molecule.
When an atom combines with another atom (or atoms) and forms a compound, it is called a molecule. A molecule is made up of two or more atoms chemically combined.
Q10. What are compounds? Give two examples.
A compound is a pure substance formed when atoms of two or more elements combine chemically in definite proportions. Examples: H₂O (water), NaCl (sodium chloride).
Q11. Give examples of elements derived from their Latin names:
| Element | Latin Name | Symbol |
|---|---|---|
| Copper | Cuprum | Cu |
| Lead | Plumbum | Pb |
| Potassium | Kalium | K |
| Iron | Ferrum | Fe |
| Mercury | Hydrargyrum | Hg |
| Sodium | Natrium | Na |
Q12. What is atomicity of elements?
Atomicity is the total number of atoms present in one molecule of an element, compound, or substance. Example: Atomicity of O₂ = 2 (diatomic), O₃ = 3 (triatomic).
Q13. Calculate the atomicity of H₂SO₄.
A molecule of sulphuric acid (H₂SO₄) consists of 2 hydrogen atoms + 1 sulphur atom + 4 oxygen atoms. Atomicity = 2 + 1 + 4 = 7.
VIII. Detailed Answer Questions
Q1. Differentiate metals and non-metals.
| Property | Metals | Non-Metals |
|---|---|---|
| Luster | Lustrous (shiny surface) | Non-lustrous (dull surface) |
| Hardness | Generally hard | Generally soft |
| Bendability | Bendable | Non-bendable |
| Malleability/Ductility | Can be bent, beaten into sheets, drawn into wires | Non-ductile, brittle |
| Electrical conductivity | Good conductors | Bad conductors (except graphite) |
| Heat conductivity | Good conductors | Bad conductors |
| Sound | Produce ringing sound when struck (sonorous) | Do not produce sound when struck |
| Examples | Copper, Lead, Tin, Nickel | Carbon, Iodine, Sulphur |
Q2. Explain the characteristics of compounds.
1. A compound forms only when constituent elements combine in a fixed proportion. 2. Properties of a compound differ from those of its constituent elements. 3. A compound cannot be broken down by physical methods (e.g., filtration cannot separate sodium chloride). 4. A compound is made of different elements chemically combined. 5. A compound can be separated into constituent elements only by chemical methods (e.g., electrolysis).
Q3. Describe the different ways of writing symbols of elements with examples.
1. Chemical symbols usually consist of one or two letters. 2. The symbol of most elements corresponds to the first letter (capitalized) of their English name. Example: "O" for oxygen, "H" for hydrogen. 3. When more than one element begins with the same letter, their symbols take two letters — the first letter capitalized and the second letter lowercase. Example: Hydrogen = H, Helium = He. 4. Some symbols are derived from Latin names. Example: Iron = Fe (from Ferrum), Sodium = Na (from Natrium).
Q4. Differentiate between elements and compounds.
| Elements | Compounds |
|---|---|
| The simplest form of pure substance | A chemical substance formed by combination of two or more elements |
| Elements combine to form compounds | Compounds can be split into elements |
| Atoms are the fundamental particles | Molecules are the fundamental particles |
| Made of one kind of atom | Made of two or more kinds of atoms |
Q5. Write any five characteristics of compounds.
1. A compound forms when constituent elements combine in a fixed proportion. 2. Properties of a compound differ from its constituent elements. 3. A compound cannot be broken down by physical methods. 4. A compound is made of different elements chemically combined. 5. A compound can be separated into constituent elements only by chemical methods.
Q6. List comparative properties of metals and non-metals with three examples each.
| Property | Metals | Non-Metals |
|---|---|---|
| Luster | Lustrous | Not lustrous |
| Conductivity | Good conductors | Poor conductors (except graphite) |
| Malleability | Malleable and ductile | Neither malleable nor ductile |
| State at room temp. | Mostly solid (except Hg) | Solid, liquid, or gas |
| Examples | Copper, Iron, Silver | Carbon, Iodine, Sulphur |
Q7. Write down the properties of metalloids.
1. Metalloids usually look like metals but behave largely like non-metals. 2. Physically they are shiny, brittle solids with intermediate to relatively good electrical conductivity. 3. They can form alloys with metals. 4. Most physical and chemical properties are intermediate in nature. 5. They are semiconductors. 6. All are solids at room temperature. 7. Examples: Germanium, Boron, Antimony, Silicon.
IX. Rewrite the Sentence in Correct Form
Q1. "Elements contains two or more kinds of atoms and compounds contains only one kinds of atoms."
Corrected: Elements contain only one kind of atom and compounds contain two or more kinds of elements.
X. Assertion-Reason Questions
Key: A = Both true, 2nd explains 1st; B = Both true, 2nd doesn't explain 1st; C = 1st false, 2nd true; D = Both false.
| # | 1st Statement | 2nd Statement | Answer |
|---|---|---|---|
| 1 | Oxygen is an element | Oxygen cannot be broken down into anything simpler | A |
| 2 | Hydrogen is an element | Hydrogen cannot be broken down into anything simpler | A |
| 3 | Air is a compound | Air consists of carbon dioxide | D — Both false. Air is a mixture of gases; air consists mainly of Nitrogen, Oxygen, CO₂, and noble gases. |
| 4 | Air is a mixture of elements only | Only nitrogen, oxygen and neon gases exist in air | A |
| 5 | Mercury is solid at room temperature | Mercury is a non-metal | D — Both false. Mercury is liquid at room temperature; mercury is a metal. |
XI. Higher Order Thinking Questions (HOTS)
Q1. List metals, non-metals, and metalloids used in your house/school. Compare their properties.
Metals used: Magnesium (lab ribbon), Copper (cooking utensils), Zinc (protective coat for iron gates), Aluminium (cooking utensils, electrical cables), Iron/steel (construction), Sodium (table salt), Nickel (coins), Lead (car batteries).
Non-metals used: Oxygen (breathing, lab oxidising agent), Chlorine (water purification), Graphite (pencil leads), Carbon (fuel), Bromine (dyes), Iodine (starch test).
Metalloids used: Silicon (glass items), Antimony (optical discs), Tellurium (solar cells), Boron (washing powders), Germanium (transistors).
| Property | Metals | Non-metals | Metalloids |
|---|---|---|---|
| Luster | Lustrous | Not lustrous | Intermediate |
| Conductivity | Good conductors | Poor (except graphite) | Semi-conductors |
| Malleability | Malleable and ductile | Neither malleable nor ductile | Intermediate |
Q2. Aakash noticed the metal latch on a gate was difficult to open on hot sunny days but not at night.
(a) Hypothesis: Solids (like iron) expand on heating and contract on cooling. During expansion, volume increases but mass stays the same. (b) Testing explanation: When heated, distance between iron particles increases, making the latch tight and hard to open. At night, cooling decreases the distance between particles, making it easy to open.
Q3. What changes take place in the movement and arrangement of particles during heating?
When a substance is heated, internal energy increases. Particle movement increases. Bonds between particles break during melting/evaporation, causing volume to increase. The closeness, arrangement, and motion of particles change when state changes, but particle size (mass) remains the same.
Q4. Why is hydrogen considered an element?
Hydrogen cannot be broken into new substances by ordinary physical or chemical means. Hydrogen has only one kind of atom.
Q5. Why is water considered a compound?
Water is composed of two elements (H₂ and O₂). The ratio of hydrogen to oxygen by mass is always the same. Properties of water differ from those of its constituent elements. Water can only be decomposed into hydrogen and oxygen by chemical methods (electrolysis).
Q6. Difference between a mixture and a compound:
| Mixture | Compound |
|---|---|
| Two or more substances mixed at random | Atoms of two or more elements combine chemically in definite proportion |
| Constituents can be separated by physical methods | Constituents can be separated only by chemical methods |
| Properties are the same as constituent substances | Properties differ from constituent elements |
| No fixed composition | Fixed composition |
XII. Complete the Table Exercises
Table 1: Compounds and Constituent Elements
| Compound | Constituent Elements |
|---|---|
| Sodium carbonate | Sodium, Carbon, Oxygen |
| Water | Hydrogen, Oxygen |
| Calcium oxide | Calcium, Oxygen |
| Sugar | Carbon, Hydrogen, Oxygen |
Table 2: Element Symbols
| Element | Symbol |
|---|---|
| Aluminium | Al |
| Nickel | Ni |
| Bromine | Br |
| Helium | He |
| Magnesium | Mg |
Table 3: Latin Names and Symbols
| Element | Latin Name | Symbol |
|---|---|---|
| Mercury | Hydrargyrum | Hg |
| Lead | Plumbum | Pb |
| Iron | Ferrum | Fe |
| Potassium | Kalium | K |
Common Mistakes to Avoid
1. Confusing elements and compounds — Elements are made of one kind of atom; compounds contain two or more kinds of atoms chemically combined. 2. Saying graphite is a metal — Graphite conducts electricity but is a non-metal (form of carbon). 3. Confusing atomicity with atomic number — Atomicity is the number of atoms in a molecule; atomic number is the number of protons. 4. Writing symbols incorrectly — First letter is always capital, second letter is always lowercase (e.g., Na, not NA or na). 5. Saying mixtures and compounds are the same — Mixtures can be separated physically; compounds can only be separated chemically. 6. Forgetting mercury is a metal that is liquid — Mercury (Hg) is the only metal that is liquid at room temperature; it is NOT a non-metal. 7. Confusing molecule and atom — An atom is the smallest unit of an element; a molecule is formed when two or more atoms combine.
Exam Checklist
- [ ] Can define element, compound, and mixture with examples
- [ ] Can classify substances as element, compound, or mixture
- [ ] Can differentiate metals, non-metals, and metalloids with examples
- [ ] Can write chemical symbols correctly (capital first letter, lowercase second)
- [ ] Know Latin-derived symbols (Fe, Cu, Na, K, Hg, Pb)
- [ ] Can write chemical formulas for common compounds (H₂O, NaCl, CO₂, H₂SO₄)
- [ ] Can calculate atomicity of molecules
- [ ] Can list five characteristics of compounds
- [ ] Can explain why water is a compound and not a mixture
- [ ] Can compare properties of metals, non-metals, and metalloids
- [ ] Can identify elements from their symbols and vice versa