Matter Around Us | Term 1 Unit 3 | 7th Science - Molecules | 7th Science : Term 1 Unit 3 : Matter Around Us
Chapter: 7th Science : Term 1 Unit 3 : Matter Around Us
Molecules
Molecules
When an atom combines with another
atom (or atoms) and forms a compound it is called as molecule.
A
molecule is made up of two or more atoms chemically combined.
* Oxygen gas in the air that we
breathe is made up of two oxygen atoms chemically combined.
* Ozone is a substance that is made
up of three oxygen atoms chemically combined.
An atom of oxygen (O) and two atoms
of hydrogen (H2) combine to form a molecule of water (H2O).
Molecules also exhibit properties of
matter and have individual existence. A molecule can be formed by the same or
different kinds of atoms.
Molecules can be
classified as follow :
* A molecule which contains only one
atom is called monatomic molecule (inert gases)
* A molecule which contains two
atoms is called diatomic molecule (oxygen, nitric oxide, hydrogen, etc.)
* A molecule containing three atoms
is called a triatomic molecule (ozone, sulphur dioxide, carbon dioxide, etc.)
* A molecule containing more than 3
atoms are known as polyatomic molecule (phosphate, sulphur, etc.)
Molecules of Elements
A molecule of an element consists of
a fixed number of one types of atom chemically combined.
The table below shows gases that are
made up of two atoms of the same type of element.
Molecules of Compounds
Molecule of a compound consists of a
fixed number of different types of atoms chemically combined.
For example, let us look at the
model of a water molecule below:
Each molecule of water consists of one oxygen atom and two hydrogen atoms. This ratio of oxygen and hydrogen atom remains fixed whether water is in liquid, solid or gaseous state. This principle applies to the molecules of all compounds.
Bismuth in diarrhea medicine
Bismuth is an element that occurs naturally. It is combined
with other elements to make medicine for treating diarrhea.
Molecules of some compounds
Classification of Matter
Matter is classified into two broad categories,
namely, pure substances and mixtures. Pure substances are further divided into
categories as elements and compounds.
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