What are the Types of Pure Substances?

Question 1

Who was the first scientist to use the term element? And in what year?

Answer 1

Robert Boyle, 1661.

Question 2

Which scientist established an experimentally useful definition of an element? And what did he define it as?

Answer 2

Antoine Laurent Lavoisier, a French chemist defined an element as a basic form of matter that cannot be broken down into simpler substances by chemical reactions.

Question 3

List five properties of metals and give two examples.

Answer 3

1. lustre
2. silvery-grey or golden-yellow colour
3. conduct heat and electricity
4. ductile
5. malleable
6. sonorous
   Gold, silver, copper, iron, sodium, and potassium.

Question 4

List some properties of non-metals and give two examples.

Answer 4

1. variety of colours
2. poor conductors of heat and electricity
3. not lustrous
4. not sonorous
5. not malleable
   Hydrogen, oxygen, iodine, carbon (coal, coke), bromine, chlorine.

Question 5

What are metalloids? List two examples of metalloids.

Answer 5

Elements which have intermediate properties between those of metals and non-metals are called metalloids. Examples are boron, silicon, germanium, etc.

Question 6

How many elements are naturally occurring?

Answer 6

92

Question 7

Majority of elements are solids. True of False.

Answer 7

True

Question 8

How many elements are in gaseous state at room temperature?

Answer 8

11

Question 9

Give two examples of elements that are liquid at room temperature.

Answer 9

Mercury and bromine.

Question 10

Which two elements become liquid at a temperature slightly above room temperature?

Answer 10

Gallium and caesium.

Question 11

Define compounds.

Answer 11

A substance composed to two or more elements, chemically combined with one another in a fixed proportion.

Question 12

List the properties of a compound.

Answer 12

1. composition remains the same throughout.
2. we get a compound when heating two elements strongly, which has different properties than the combining elements.
3. texture and the colour of the compound are the same throughout.

Question 13

DID YOU LEARN ACTIVITY 2.4 ON PAGE 20?

Answer 13

Yes

Question 14

Differentiate between mixture and compound.

Answer 14

MIXTURE
1. elements or compounds are just mixed together to form a mixture and no new compound is formed.
2. has a variable composition.
3. shows properties of constituent substances
4. constituents can be separated easily by physical methods

COMPOUND
1. elements react to form new compounds
2. composition of each new substance is always fixed
3. new substance has totally different properties
4. constituents can be separated only by chemical or electrochemical reactions.