ICSE Class 6 Chemistry Important Questions Chapter 3 Element and Compounds

Chemistry ICSE Class 6 Important Questions Chapter 3 Element and Compounds

Practice Questions

Question 1.
Define –
1. Element
2. Atom
Answer:
1. An element is a pure substance which cannot be broken down into simpler substances by any physical or ordinary chemical means.
2. An atom is the smallest particle of an element which possesses all the properties of that element and may or may not have independent existence.

Question 2.
Who introduced the present system of allotting symbols to the elements ?
Answer:
Swedish scientist J.J. Berzelius

Question 3.
What is fuel form of IUPAC ?
Answer:
IUPAC – International Union of Pure and Applied Chemistry.

Question 4.
Give symbols for chlorine, calcium, magnesium, phosphorous.
Answer:
Chlorine – Cl
Calcium – Ca
Magnesium – Mg
Phosphorous – P

Question 5.
Write molecular formula for common salt (sodium chloride), hydrogen chloride, nitrogen dioxide, ammonia, iron oxide, magnesium oxide.
Answer:
Common salt (sodium chloride) – NaCl
Hydrogen Chloride – HCl,
Nitrogen dioxide – NO₂
Ammonia – NH₃
Iron oxide – FeO
Magnesium oxide – MgO

Question 6.
Mention characteristics of an atom.
Answer:

1. The atoms of most elements are very reactive and do not exist as free atoms, (except for atoms of noble gases)
2. All atoms of an element are similar or identical.
3. The atoms of one element are different from those of other elements.
4. An atom maintains its properties through all physical and chemical changes.

Question 7.
Write differences between an atom and a molecule.
Answer:
Atom :

1. An atom is the smallest particle of an element which generally does not exist independently
2. Highly reactive, except noble gas atoms.
3. Cannot be subdivided.
4. No chemical bond in atom.

Molecule :

1. A molecule is the smallest particle of an element or compound which exists independently.
2. Less reactive.
3. Can be subdivided into atoms.
4. Atoms in a molecule are held together by chemical bonds.

Question 8.
Give one example each of monoatomic, diatomic, triatomic and polyatomic molecules.
Answer:
Monoatomic molecule – Helium (He)
Diatomic molecule – Oxygen (O₂)
Triatomic molecule – Ozone (O₃)
Polyatomic molecule – Phosphorous (P₄)

Question 9.
What is the significance of the molecular formula of a compound ?
Answer:
The molecular formula of a compound indicates.

1. the name of the compound.
2. the elements constituting the compound and
3. the number of atoms of various elements present in one molecule of that compound.

Question 10.
Fill in the blanks.
1. There are ………… known elements today, out of which, ………….. are naturally occurring elements.
Answer:
There are 118 known elements today, out of which, 92 are naturally occurring elements.

2. ………….. is a metal and ………….. is a non-metal that are liquids at room temperature.
Answer:
Mercury is a metal and bromine is a non-metal that are liquids at room temperature.

3. The atoms in a molecule are held together by attractive forces called …………..
Answer:
The atoms in a molecule are held together by attractive forces called chemical bonds.

4. The smallest particle of an element is its ………….
Answer:
The smallest particle of an element is its atom.

5. The smallest particle of a compound is its ………….
Answer:
The small est particle of a compound is its molecule.

6. A molecule of a substance can be represented by its …………
Answer:
A molecule of a substance can be represented by its molecular formula.

7. The combining capacity of an element is known as its ……….
Answer:
The combining capacity of an element is known as its valency.

ICSE Class 6 Chemistry Important Questions