• Physical nature of Matter:
• Matter is made up of very small particles. These small particles are called atoms.
• These particles cannot be seen by a naked eye, as they are too small in size.
• Atoms can be observed under electron microscope.

• Diffusion:
  Particles of matter intermix on their own with each other. They do so by getting into the spaces between the particles. This intermixing of particles of two different types of matter on their own is called diffusion.
  
  
• Brownian Motion: The random or zig-zag movement of microscopic particles in a fluid, as a result of continuous bombardment from molecules of the surrounding medium, is known as Brownian motion. For example: Dust moves randomly because the random moving particles of air collide with dust particles.
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• Anything that occupies space and has mass is called matter.
• The entire universe is composed of matter. However, few things like heat, sound, light, and electricity cannot come under the term matter, because they do not have mass, but they can be useful to do work.
• Heat can be used to iron clothes, cook food, water, etc.
• Electricity has multiple uses like making the fans revolve, useful in operating machines, etc. Our eardrums vibrate due to sound.
• Plant use light to create their food. Light is also useful during the night time to work or study. 
• All these things are forms of energy. Energy means the ability to do work.
• It exists in the form of five basic elements, the Panch tatva – air, earth, fire, sky and water. For example: Chair, bed, river, mountain, dog, tree, building, etc. Everything is made up of matter.
• In this chapter we will study the different states of matter such as solid, liquid, and gaseous.

• Substance: Matter is made of one or more components known as substances.
• Pure Substance: A substance which has only one component and nothing else in it is called a pure substance. 
• Impure substance: Impure substance is any substance of interest that contains some (small or large) amount of unwanted material.

Concept of Substance (Matter):

• Matter is made of one or more components known as substances.
• A substance is a matter that has definite properties and composition. Every pure compound and element is a substance.
• Example: Iron, Sodium chloride, etc.

Properties of Substance:

• A substance is a kind of matter which cannot be separated into any other type of matter by some physical means.
• The substance must be composed of atoms and molecules
• The substance must have a particular amount of weight, mass, and volume.

Types of Substance:

1) Pure Substance:

• A substance which has only one component and nothing else in it is called a pure substance.
• A pure substance is anything composed of a single type of material. In other words, it is free of contaminants.
• So, in addition to elements, compounds, and alloys, a pure substance might include honey, even though it consists of many different types of molecules. If you add corn syrup to the honey, you no longer have pure honey. Pure alcohol could be ethanol, methanol, or a mixture of different alcohols, but as soon as you add water (which is not alcohol), you no longer have a pure substance.

• Example of the pure substance are as follows:

  1. Tin
  2. Sulphur
  3. Diamond
  4. Sugar
  5. Water

2) Impure substance:

• Impure substance is any substance of interest that contains some (small or large) amount of unwanted material.
• Impure substance contains a random amount of constituent particles which is nothing but the mixture, which itself do not contain a fixed amount of matter.

• Example of impure substance are as follows:

  1. Salt mixed in water
  2. Chocolate chips dipped in cookies
  3. Fruit salad
  4. Muddy  water
  5. Milk and cereals
  6. Vegetable soup
  7. Rocks
  8. Sand mixed in water
  9. Sandwich
  10. Milkshake