The matter is anything that occupies space and has mass. All physical objects are composed of matter, and an easily observed property of matter is its state or phase. We will also learn the atomic structure of solids, liquids, and gases. Further in the chapter, we will also learn that the states of matter are interconvertible. The state of matter can be changed by changing temperature or pressure. 

Matter is everything in this universe that occupies space and mass. The matter is particulate in nature. Particles of matter have spaces between them, are moving all the time, and attract each other.

There are various states of matter because of variations in the characteristics of particles of matter. There are three states of matter: They are solids, liquids, and gases. The atoms or molecules are packed together much more tightly in a solid than in a gas or a liquid. Whereas in liquid they can move freely and have greater space between each other as compared to in the solid state.

The states of matter can also be changed. When the matter is heated enough, the molecules move faster and with greater energy. If enough heat is added, a solid can become liquid and a liquid can become gas. In the same way, molecules slow down when they are cooled.