Chemistry is often referred to as a "science center"

Chemistry is often referred to as the "central science" because it connects various other sciences, like physics, materials science, nanotechnology, biology, pharmacy, medicine, bioinformatics, and geology [1]. This connection arises through the various sub-disciplines that utilize concepts from various disciplines. For example, physical chemistry involves the application of physical principles to the matter at the atomic and molecular level.

Chemicals associated with the interaction of matter that may involve two substances or between matter and energy, especially in conjunction with the first law of thermodynamics. Traditional chemistry involves interactions between chemicals in a chemical reaction, which converts one or more substances into one or more other substances. Sometimes the reaction is driven by enthalpy considerations, such as when two high berentalpi substances such as elemental hydrogen and oxygen react to form water, a substance with a lower enthalpy. Chemical reactions can be facilitated by a catalyst, which is generally an other chemicals involved in the reaction media but not consumed (eg sulfuric acid which catalyzes the electrolysis of water) or immaterial phenomena (such as electromagnetic radiation in photochemical reactions). Traditional chemical analysis also handle chemical substances, both inside and outside of a reaction, such as in spectroscopy.

All normal matter consists of atoms or subatomic components that make up atoms: protons, electrons, and neutrons. Atoms can be combined to produce more complex forms of matter such as ions, molecules or crystals. The structure of the world that we live everyday and properties of matter that interacts with us is determined by the properties of chemical substances and their interactions. Steel harder than iron because its atoms are bound in the crystal structure is more rigid. Wood burning or experiencing rapid oxidation because it can react spontaneously with oxygen in a chemical reaction if it is above a certain temperature.

Substances tend to be classified on the basis of energy, phase, or its chemical composition. The material can be classified into 4 phases, the sequence of which has the lowest energy is a solid, liquid, gas, and plasma. Of the four types of this phase, the phase of the plasma can only be found in outer space in the form of stars, because of its energy needs are very great. Solids have a fixed structure at room temperature that can defy gravity or other weak forces are trying to change it. Liquids have limited bonds, without structure, and will flow with gravity. Gases have no bonds and act as free particles. Meanwhile, the plasma consists of ions that move freely; supply of energy that prevents excess ions are united into the particle element. One way to distinguish three phases of the first is with the volume and shape: roughly, to own solid volume and fixed shape, liquids have a fixed volume but no fixed shape, whereas gases have neither fixed volume or shape.