Important points and formula of chemistry for class 9 chapter-Is matter around us is pure

Important points and formula of chemistry for class 9 chapter-Is matter around us is pure

May 13, 2022, 16:45 IST

Class-9 chapter-Is matter around us is pure

A pure substance consists of particles of only one kind of matter which are similar to one another and which cannot be separated into other kinds of matter by any physical process. Furthermore, a pure substance has a uniform composition throughout. Pure substances are classified into two categories, le, elements and compounds.

Element, Compound and Mixture

An element is defined as the simplest form of a pure substance which can neither be broken into nor built from simpler substances by any physical or chemical method. For example, hydrogen, oxygen, mercury, gold, iron, copper, etc.

Elements are further classified into metals, non-metals and metalloids or semi-metals

• Metals possess luster. They are malleable and ductile, good conductors of heat and electricity and are sonorous. For example, iron, copper, mercury, sodium, etc.
• Non-metals are neither malleable nor ductile. They are not lustrous and are non-conductors of heat and electricity. For example, hydrogen oxygen, bromine, sulphur phosphorus, etc
• Metalloids or semi-metals have properties in between those of metals and nonmetals. For example, silicon, germanium, arsenic, antimony and tellurium.

1. A compound is defined as a pure substance made up of two or more elements chemically combined in a fixed proportion by mass. For example, water, carbon dioxide, lime stone, etc.
2. Mixtures. A mixture contains two or more substances (elements or compounds), which are physically mixed in any proportion but not chemically combined. Thus, mixtures have carriable  composition and hence no definite formula can be assigned to a mixurte.

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