matter
In physics, anything that has mass. All matter is made up of atoms, which in turn are made up of elementary particles; it ordinarily exists in one of three physical states: solid, liquid, or gas.
States of matter
Whether matter exists as a solid, liquid, or gas depends on its temperature and the pressure on it.
Kinetic theory describes how the state of a material depends on the movement and arrangement of its atoms or molecules. In a solid the atoms or molecules vibrate in a fixed position. In a liquid, they do not occupy fixed positions as in a solid, and yet neither do they have the freedom of random movement that occurs within a gas, so the atoms or molecules within a liquid will always follow the shape of their container. The transition between states takes place at definite temperatures, called melting point and boiling point.
Conservation of matter
In chemical reactions matter is conserved, so no matter is lost or gained and the sum of the mass of the reactants will always equal the sum of the end products.
| The history of science and philosophy is largely taken up with accounts of theories of matter, ranging from the hard atoms of Democritus to the ‘probability waves’ of modern quantum theory. The earliest theory of matter of any importance is that of Democritus and Lucretius, who supposed that matter consisted of hard atoms that could neither be created, destroyed, nor altered in any way. In the 19th century, investigations into the nature of combustion and chemical combination led to the firm identification of the atomic nature of the elements, and to the understanding that these atoms combined to form molecules, the smallest particles of chemical compounds (see atomic structure). The kinetic theory of matter, the theory of the motion of these atoms and molecules in gases, liquids, and solids, successfully accounted quantitatively for many of the phenomena of gases, liquids, and solids. In particular heat energy was shown to consist simply of the kinetic energy of the chaotic motion of the atoms and molecules in matter. Electrical research initiated by English physicist J J Thomson in the last decade of the 19th century heralded the spectacular progress in understanding of the 20th century. While the atom of English chemist John Dalton was the ‘ultimate particle’ in chemical reactions, it proved to be divisible by electrical means, when Thomson identified the existence of the electron, a particle carrying a negative charge of electricity, and of mass nearly 2,000 times smaller than the lightest atom, hydrogen. Its mass and electrical charge were determined by US physicist Robert Millikan. Researchers in radioactivity gradually established that in addition to negatively charged electrons, all matter is composed of positively charged protons, uncharged neutrons, and other shorter-lived particles. |
