ICSE Class 7 Chemistry Important Questions Chapter 1 Elements and Compounds

Chemistry ICSE Class 7 Important Questions Chapter 1 Elements and Compounds

Question 1.
List few characteristics of elements.
Answer:

• An element is a pure substance made up of only one kind of atoms.
• Atoms of an element cannot be broken down by physical or chemical means.
• An element has its own fixed melting point and boiling point.
• It may occur naturally or may be prepared.

Question 2.
What are metalloids ? Give two properties and examples.
Answer:
Elements having intermediate properties between those of metals and non-metals are called metalloids.

Properties :
(i) They are solids at room temperature.
(ii) They are brittle rather than malleable.
Examples : Silicon, germanium, etc.

Question 3.
Different between metals and non-metals with respect to their properties.
Answer:
Metals :

1. They are usually solids at room temperature.
2. They are generally quite hard.
3. They are good conductors of heat and electricity.
4. They have a lustre.
5. They are malleable and ductile.
6. They are sonorous.
7. They have high melting and boiling points.
8.  Examples : Gold, silver, copper, sodium, iron etc.

Non-metals :

1. They exist as solids or gases at room temperature.
2. The solid non-metals are brittle.
3. They are bad conductors of heat and electricity except graphite.
4. They are not lustrous.
5. They are not malleable and not ductile.
6. They are not sonorous.
7. They have low melting and boiling points.
8. Examples : carbon, oxygen, nitrogens sulphur, bromine, etc.

Question 4.
What are inert or noble gases ?
Answer:
The elements which do not ordinarily combine with other elements to form compounds are called inert or noble gases. These elements are colourless gases. Examples : Helium, neon, argon, krypton, xenon and radon.

Question 5.
Give symbols for the following elements :

1. Cobalt
2. Manganese
3. phosphorous
4. silicon
5. sodium
6. helium
7. tin
8. lead
9. gold
10. mercury.

Answer:

1. Cobalt – Co
2. Manganese – Mn
3. phosphorous – P
4. silicon – Si
5. sodium – Na
6. helium – He
7. tin – Sn
8. lead – Pb
9. gold – Au
10. mercury – Hg

Question 6.
Why is valency of noble gases zero ?
Answer:
Noble gases do not gain or lose electrons and do not combine with other elements to form compounds, hence their valency is zero.

Question 7.
Write the cations, anions and polyatomic ions present in the following compounds:

1.  Ammonium chloride (NH₄Cl)
2. Magnesium oxide (MgO)
3. Copper sulphate (CuSO₄)
4. Ammonium nitrate (NH₄NO₃)

Answer:
1. Ammonium chloride (NH₄Cl) – Polyatomic cation is NH⁺₄ (ammonium ion) .
Anion is Cl^– (chloride ion)

2. Magnesium chloride (MgO) – Cation is Mg²⁺ (magnesium ion)
Anion is O^2- (oxide ion)

3. Copper sulphate (CuSO₄) – Cation is Cu²⁺ (Copper (II) ion)
Polyatomic anion is SO₄^2- (sulphate ion)

4. Ammonium nitrate (NH₄NO₃) – Polyatomic cation is NH⁺₄ (ammonium ion)
Polyatomic anion is NO₃^– (nitrate ion)

Question 8.
What is the significance of a chemical formula ?
Answer:
The chemical formula of a compound indicates the following things.

1. the name of the compound
2. the elements or ions constituting the compound.
3. the number of atoms of various elements or ions present in one
4. molecule of the compound, and
5. one molecule of the compound.

Question 9.
Name the following :
1. Metal which is liquid at room temperature.
Answer:
Mercury

2. two metals which are soft
Answer:
Sodium and potassium

3. One hard non-metal
Answer:
Diamond (a form of carbon)

4. One non-metal which is a good conductor of electricity.
Answer:
Graphite (a form of carbon)

5. Two non-metals which have metallic lustre.
Answer:
Graphite and iodine

6. One non-metal having high melting point
Answer:
Diamond (a form of carbon)

7. Two elements which are .liquid at room temperature.
Answer:
Mercury and bromine

8. Two metals which can exist as liquids at a temperature . around 30°C
Answer:
Gallium and caesium

9. An atom which has eight atoms in its molecule (atomicity is 8)
Answer:
Sulphur (Sg)

Question 10.
Fill in the blanks.
1.  About 93% of atoms in the entire universe are ………… atoms.
Answer:
About 93% of atoms in the entire universe are hydrogen atoms.

2. …………. and ………… are the main elements present in stars.
Answer:
Hydrogen and helium are the main elements present in stars.

3. The majority of the elements are ………….. eleven are ………….. while only ………… are liquid at room temperature.
Answer:
The majority of the elements are solids, eleven are gaseous ” while only two are liquid at room temperature.

4. ………….. is the best conductor of heat and electricity.
Ansswer:
Silver is the best conductor of heat and electricity.

5. ……………… is the most malleable and ductile metal.
Answer:
Gold is the most malleable and ductile metal.

6. Latin name of iron (Fe) is ………. while of sodium (Na) is
Answer:
Latin name of iron (Fe) is ferrum while of sodium (Na) is natrium.

7. The word ‘atomos’ was first coined by
Answer:
The word ‘atomos’ was first coined by Democritus.

8. …………….. put forward the atomic theory.
Answer:
John Dalton put forward the atomic theory.

9. Generally ………….. lose electrons to form positive ions and …………. gain electrons to form negative ions.
Answer:
Generally, metals lose electrons to form positive ions and non metals gain electrons to form negative ions.

10. …………… is the only polyatomic cation.
Answer:
Ammonium ion (NH4+) is the only polyatomic cation.

11. A …………… is formed when atoms of different elements join together chemically.
Answer:
A compound is formed when atoms of different elements join together chemically.

12. …………….. can be monoatomic or polyatomic.
Answer:
Ions can be monoatomic or polyatomic.

Concept Map :

ICSE Class 7 Chemistry Important Questions