Basic Concepts

Chemistry: The science that deals with composition, structure, properties and interaction of matter is called chemistry.

Matter: Anything which occupies space and has mass is called matter.

States of Matter:

There are three states of matter, viz. solid, liquid and gas.

  1. Solid: It has definite shape and definite volume.
  2. Liquid: It has definite volume but indefinite shape.
  3. Gas: It has indefinite volume and indefinite shape.

The three states of matter are inter-convertible by changing conditions of temperature and pressure.

Classification of Matter:

There are two broad types of matter, viz. pure substance and mixture.

  1. Pure Substance: When matter is made up of only one kind of particles, it is called pure substance. Pure substances are of two types, viz. element and compound.
    1. Element: When matter is made of only one kind of atom, it is called element.
    2. Compound: When matter is made up of two or more kinds of atom, and atoms of different elements are combined in definite proportion, it is called compound. Constituents of a compound cannot be separated by physical method. They can, however, be separated by applying chemical method.
  2. Mixture: When matter is made up of more than one kind of particles, it is called mixture. There are two types of mixture, viz. homogeneous and heterogeneous mixtures.
    1. Homogeneous Mixture: When components of a mixture are thoroughly mixed and uniformly distributed throughout the bulk, it is called homogeneous mixture. Solution and colloid are homogeneous mixture.
    2. Heterogeneous Mixture: When components of a mixture are not mixed thoroughly, it is called heterogeneous mixture. Suspension is heterogeneous mixture.

NOTE: For notes on measurement of physical properties of matter, you can view notes for Chapter 1 of Class 11 Physics on our website.

Laws of Chemical Combination

Law of Conservation of Mass: This law was given by Antoine Lavoisier in 1789. This law says that matter can neither be created nor destroyed.

Law of Definite Proportions: This law was given by Joseph Proust from France. This law says that a given compound always contains exactly the same proportion of elements by weight. This law is also referred to as the Law of Definite Composition.

Law of Multiple Proportions: This law was given by Dalton in 1803. This law says that if two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element, are in the ratio of small whole numbers.

Example: Hydrogen combines with oxygen to form two compounds, viz. water and hydrogen peroxide.

Hydrogen (2g) + Oxygen ¬(16g) → Water (18g)

Hydrogen (2g) + Oxygen (32g) → ¬ Hydrogen Peroxide (34g)

It can be noted that the masses of oxygen (16g and 32 g) which combine with a fixed mass of hydrogen (2g) bear a simple ratio, i.e. 16 : 32 or 1 : 2

Gay Lussac’s Law of Gaseous Volumes: This law was given by Gay Lussac in 1808. This law says that when gases combine in a chemical reaction, they combine in a simple ratio by volume, provided all gases are at the same temperature and pressure.

Example: Following equation shows combination of hydrogen and oxygen to produce water.

Hydrogen (100 mL) + Oxygen (50 mL) → Water (100 mL)

Here, hydrogen and oxygen combine in a simple ratio, i.e. 2 : 1

In fact, this law is the law of definite proportion by volume.

Avogadro’s Law: This law was given by Avogadro in 1811. This law says that equal volumes of all gases at the same temperature and pressure should contain equal number of molecules.

Dalton’s Atomic Theory:

Dalton published ‘A New System of Chemical Philosophy’ in 1808 in which he proposed the following:

Dalton’s theory could explain the laws of chemical combination. However, it could not explain the laws of gaseous volumes. Moreover, it could not provide the reason for combining of atoms.

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