The Chemistry Book

In most middle schools, students are introduced to the concept of matter. The simple definition is matter is anything which has mass and occupies space. In high school chemistry, students expand on this definition by classifying the matter as mixtures or pure substances and relate the different models of an atom's structure to matter. Matter is also found in different forms (called phases or states of matter).

The concept of matter has changed dramatically over the past two centuries. First matter consists of a basic substances, the element, with defined physical and chemical properties. Initially, atoms were believed to the be the basic building blocks of matter. With the discovery of different subatomic particles, the complexity of the atom created debates regarding its structure. The latest model of the atom is the Standard Model.