Page 105 - Innovator's Science-8

When you bring a burning candle near the mouth of the two test tubes, the
reactions of the gases help identify them. In one test tube, you hear a small

pop sound when the candle is brought close—this shows that the gas inside
is hydrogen because hydrogen burns quickly with a popping noise. In the
other test tube, the candle flame glows brighter instead of popping—this
means that the gas in that tube is oxygen, which supports burning and

makes flames burn more brightly.

Flame glows
Pop sound brighter

Test tube Candle
Test tube
stand
Water Water

(a) (b)
Testing the nature of gas (a) hydrogen; (b) oxygen

We can infer that water is composed of two different constituents—
hydrogen and oxygen.

Water Hydrogen + Oxygen

ELEMENTS

According to the above activity the hydrogen and oxygen obtained are pure
substances known as elements. An element is made up of only one kind of
particle, called atoms, and these atoms are different from the atoms of any

other element. Elements cannot be broken down into simpler substances,
and they serve as the basic building blocks for all matter. Examples of other
a.
elements include gold, silver, sulfur, and carbon.

Elements can be classified into metals and non-metals. You have already
studied that gold, silver, magnesium, iron, and aluminium are metals,
whereas carbon, sulfur, hydrogen, and oxygen are non-metals. Isn't it

interesting to know that some elements like silicon and boron have
b.
intermediate properties between those of metals and non-metals? They
Depiction of are called metalloids, about which you will learn in higher grades.
molecules of
(a) hydrogen;
(b) oxygen COMPOUNDS
We cannot separate hydrogen and oxygen in water by just physical means
because, in water, their particles are strongly joined together in a way that

forms an entirely new substance. This is why water is called a compound; it
is made when different elements combine in a fixed ratio through a

105
Science-8