From the CISCE curriculum. 4 key concepts, about 2 days of study at 20 to 30 minutes a day.
Objects that take shape and have mass are called matter. A block of wood, milk and air are all made of matter. Matter is made up of tiny particles called atoms and molecules that cannot be seen by the human eye as they are very small. Matters exists in form of solid, liquid or gas. A solid has a certain size and shape, like a block of wood. A liquid, like water, has a size but does not have a definite shape. It takes the shape of the container it is put in. A gas, like air, is a form of matter that has no definite shape or size.
From the CISCE Curriculum for Classes I to VIII (2016). CISCE sets what is taught, not the textbooks, so schools use different books and there are no page numbers here. Adhian Gurus is not affiliated with CISCE.