7th Std Science Term 1 Solution in English | Lesson.3 Matter Around Us

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Lesson 3. Matter Around Us

Matter Around Us Book Back Solution 2021 - 2022

Lesson 3. Matter Around Us

I . Choose the correct answer.

1. Which of the following is an example of a metal?

  1. Iron
  2. Oxygen
  3. Helium
  4. Water

Ans : Iron

2. Oxygen, hydrogen, and sulphur are examples of which of the following?

  1. Metals
  2. Non-metals
  3. Metalloids
  4. Inert gases

Ans : Non-metals

3. Which of the following is a short and scientific way of representing one molecule of an element or compound?

  1. Mathematical formula
  2. Chemical formula
  3. Mathematical symbol
  4. Chemical symbol

Ans : Chemical formula

4. The metals which is a liquid at room temperature

  1. Chlorine
  2. Sulphur
  3. Mercury
  4. Silver

Ans : Mercury

5. An element which is always lustrous, malleable and ductile

  1. non-metal
  2. metal
  3. metalloid
  4. gas

Ans : metal

II. Fill in the blanks:

1. The smallest particle of matter that can exist by itself .

Ans : Atom

2. A compound containing one atom of carbon and two atoms of oxygen is .

Ans : Carbon-di-oxide

3. ……..is the only non-metal conducts electricity.

Ans : Graphite

4. Elements are made up of kinds of atoms.

Ans : Same

5. ………of some elements are derived from Latin or Greek names of the elements.

Ans : Symbols

6. There are ……….. number of known elements.

Ans : 118

7. Elements are the form of pure substances .

Ans : Simplest

8. The first letter of an element always written in……. letter

Ans : Capital

9. Molecule containing more than three atoms are known as .

Ans : Poly Atomic

10. ……… is the most abundant gas in the atmosphere.

Ans : Nitrogen

III. Fill in the Blanks

1. Mercury: liquid at room temperature: : Oxygen: ……………..

Ans : Gas at room temperature .

2. Non metal conducting electricity: ………..: : Metal conducting electricity: Copper

Ans : Graphite

3. Elements: combine to form compounds: : Compounds: ……………… .

Ans : Combine to form Mixture

4. Atoms : fundamental particle of an element: : ……………….: fundamental particles of a compound.

Ans : Molecules

IV. True of False.

1. Two different elements may have similar atoms.

Ans : False

Cu. An. : Two different elements may have different atoms.

2. Compounds and elements are pure substance. 

Ans : True

3. Atoms cannot exist alone; they can only exist as groups called molecules. 

Ans : False

Cu. An : Atoms can exist alone; they can only exist as groups called molecules.

4. NaCl represents one molecule of sodium chloride.

Ans : True

5. Argon is mono atomic gas. 

Ans : True

V. Answer in brief

1. Write the chemical formula and name the elements present in the following compounds:

a. Sodium chlorideNaclSodium, Chlorine
b. Potassium hydroxideKoHPotassium, Oxygen, Calcium
c. Carbon-di-oxideCO2Carbon, Potassium
d. Calcium oxideCaOCalcium, Potassium
e. Sulphur dioxideSO2Sulphur, Potassium

2. Classify the following molecules as the molecules of element or compound

Molecules of Compound

 

 

Molecules of Element

3. What do you understand by chemical formula of a compound? What is its significance?

A chemical formula is a symbolic representation of one molecules of an element or a compound. The chemical formula tells us the types of atoms and the number of each types of atoms in one molecules of substance.

4. Define the following terms with example of each:

(a) Element

Matter in its simple form is called an element. It cannot be broken down.

ex. Iron ore

(b) Compound

Two or more element are chemically based bonded together is called compound.

ex. Water

(c) Metal

Element or materials may be flattened into thin sheets are called as metals.

ex. Iron

(d) Non- metal

Non-metal are generally dull and soft

ex. Carbon

(e) Metalloids

Metalloids exhibit the properties of both metals and non-metal.

ex. Silicon

5. Write the symbols for the following element and classify them as solid, liquid and gas

Aluminum, carbon, chlorine, mercury, hydrogen and helium

Solids

  • Aluminium – Al
  • Carbon – C

Liquid

  • Mercury – Hg

Gas

  • Chlorine – Cl
  • Hydrogen – H2
  • Helium – He

6. Classify the following as metals, Non-metals and metalloids

Sodium, Bismuth, Silver, Nitrogen, Silicon, carbon, chlorine, Iron, copper

Metals

  • Sodium
  • Silver
  • Iron
  • Copper

Non-metals

  • Nitrogen
  • Carbon
  • Chlorine

Metalloids

  • Bismuth
  • Silicon

7. Classify the following as elements and compounds:

Water, common salt, sugar, carbon dioxide, iodine and lithium

Element

  • Iodine
  • Lithium

Compounds

  • Water
  • Common salt
  • Sugar
  • Carbon dioxide

8. Write the chemical formula for the following elements

Hydrogen

  • H2

Nitrogen

  • N2

Ozone

  • O3

Sulphur

  • S8

9. What are elements? What are they made of? Give two examples.

Matter in its simples form is called element. It cannot be broken down. Elements are made up of atoms.

ex. Iron, Silver

10. Define Molecules.

A molecule is made up of two or more atoms chemically combined.

11. What are compounds? Give two examples.

A compound is a pure substance that is formed when the atoms of two or more elements combine chemically in definite proportions.

ex. Water, Salt

12. Give an examples for the elements derived from their Latin names.

GoldAurumAu
CopperCuprumCu

13. What is atomicity of elements?

In chemistry atomicity is used to implies the total number of atoms present in one molecules of an element.

14. Calculate the atomicity of H2SO4

A molecule of sulphuric acid (H2SO4) consists of 2 hydrogen atom, 1 sulphur atom and 4 oxygen atoms.

Hence its atomicity is 2+1+4=7

VI. Answer in detail:

1. Differentiate metals and non-metals.

MetalsNon-Metals
1. Metals are lustrous. They have a shiny surface.Non-metals are non lustrous. They non shiny surfaces.
2. Metals are generally hard.Non-metals are generally soft.
3. Most metals are bendable. SI unit of velocity is metre / second
4. Most metals can be bent, beaten into sheets and they can drawn into wires.Non-metals are non ductile
5. Most metals are good conductors of electricity and heat.5. It is bad conductors of electricity and heat.
6. It making ringing sound when struck.6. Does not make any sound when they struck.

2. Explain the characteristics of compound.

  • A compound is formed only when the constituent elements combine in a fixed proportion.
  • The properties of a compound are different from those of it constituent elements.
  • A compound cannot be broken down by physical methods.
  • This is because a compound is made up of different elements that are chemically combined.
  • Sodium chloride cannot be separated by physical methods such as filtration.
  • A compound can be separated into its constituent elements by chemical methods only.

3. Describe the different ways in which we can write the symbols of element. Give approximate examples.

  • Chemical symbols usually consist of one or two letters. ex. Carbon – C
  • The symbols of most elements correspond to the first letter of their English name.
    • ex : oxygen – O, Hydrogen – H
  • When there is more than me element that begins with the same letter, symbols take two letters. The first letters is capitalised while the second letter has a lower case.
    • For ex. Hydrogen – H, Helium – He
  • The symbols for some elements are derived from their Latin names.
    • For ex. The symbol for gold is AU after its Latin name Aurum. Similarly, the symbols for copper is Cu after its Latin name Cuprum.

4. Difference between elements and compound:

ElementsCompounds
1. An element is the simplest substance.A compound is a chemical substance formed by the combination of two or more elements.
2. Elements combine to form compounds.Compound can be split into elements.
3. Atoms are the fundamental particle of an element.Molecules are the fundamental particles of a compound.

5. Write ant five characteristics of compound.

  • A compound is formed only when the constituent elements combine in a fixed proportion.
  • The properties of a compound are different from those of its constituent elements.
  • A compound cannot be broken down by physical methods.
  • A compound can be separated into its constituent elements by chemical methods only.
  • Compound exhibit properties entirely different from the properties of their constituent element.

6. Comparative properties of metals and non-metals. Give three examples of each.

MetalsNon – Metals 
1. Metals are generally hard and shiny elements.Non-metal are generally dull and soft.
2. All metals, except mercury are solids at room temperature.Non-metals such as oxygen, hydrogen and chlorine are gases at room temperature. Non-metals such as carbon, iodine, sulphur and phosphorus are solids at room temperature. Bromine is the only non-metals that liquid at room temperature.
3. Metals are malleable can be bent or beaten into sheets.Non-metals are non bendable.
4. Metals are good conductor of heat and electricity.Non-metals are poor conductors of heat and electricity.
5. Examples: Copper, Iron, GoldExamples: Carbon, Iodine, Sulphur

7. Write down the properties of metalloids.

Metalloids exhibit the properties of both metals and non-metals. Metalloids are solid at room temperature.
In metalloids, silicon and Germanium are semiconductors metalloids mixed with metals can form alloys.

VII. Rewrite the sentence in correct form:

1. Elements contain two or more kinds of atoms and compounds contain only one kind of
atom.

Compounds contains two or more kinds of atoms and elements contains only kind of atom.

VIII. Assertion-reason questions:

Directions : Please refer to the following instructions:

  1. Both statements are true and the 2nd statement is a correct explanation of the 1st statement.
  2. Both statements are true but the 2nd statement is NOT a correct explanation of the 1st statement.
  3. The 1st statement is false while the 2nd statement is true.
  4. Both statements are false.
AssertionReason
1. Oxygen is a compoundOxygen cannot be broken down into anything simpler
2. Hydrogen is an elementHydrogen cannot be broken down into anything simpler
3. Air is a compoundAir consists of carbon dioxide
4. Air is a mixture of elements onlyOnly nitrogen, oxygen and neon gases exist in air
5. Mercury is solid in room temperatureMercury is a non-metal

Ans : 1 – C, 2 – A, 3 – C, 4 – A, 5 – D


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