Electronics Basic Concepts of Matter Atoms & Molecule, The electron theory, which is now accepted and used to explain the behavior of electricity, states that electric current consists of electron flow and can be defined as a moving charge. Electricity can be defined, then, as charged matter. Because an electron, even though smaller than the smallest known microscopic organism, has mass and occupies space, it is matter. To understand what an electron is, you need first to understand the structural nature of matter.
Matter is basically composed of two kinds of electricity (positive and negative). The electron is the basic unit of negative electricity and the proton is the basic unit of positive electricity. There is also a neutral particle called the neutron.
Molecules
Matter exists in three states; solid, liquid, and gas. You are familiar with water in each of its three states; ice, water, and steam. Regardless of its state, all matter is composed of small particles known as molecules. Solids, liquids, and gases differ in the spacing and forces between the molecules. You know it takes more force to separate ice than it does liquid water. The molecules in gas (steam) will separate themselves if left alone. Molecules in any state are in constant motion.
The molecule is the smallest component into which a compound can be sub-divided by physical means. Boiling water subdivides into separate molecules without changing the chemical composition of the molecules. This is a physical change. To subdivide the molecule into its components requires a chemical change.
Molecules are composed of atoms. A substance which contains atoms of one kind only is called an element, while those containing more than one kind are called compounds or mixtures. When two or more atoms combine, they form a molecule. If these atoms are not all alike, then the substance formed is a compound. Oxygen and hydrogen are both examples of an element. When one oxygen atom and two hydrogen atoms unite, they form a molecule of water. Water is a compound.
Atoms
As mentioned above, molecules are composed of even smaller particles known as atoms. According to the present concept, an atom is one or more negatively charged particles called electrons, revolving at great speeds in regular, circular, or elliptical orbits around a positive nucleus. The nucleus is one or more positively charged particles called protons and a number of uncharged particles called neutrons. A typical atom, lithium, is shown in
Figure Atomic Structure as Shown by Lithium.
According to present theory, the nucleus of an atom always has the same number of protons in it as it has electrons outside of it. Uncharged particles, neutrons, are found in the nucleus and add weight to the atom. A proton and a neutron have the same weight, and each is approximately 1,845 times heavier than an electron. The difference between the different atoms is in the number and arrangement of the protons and electrons. Atoms of each of the known elements are of a different weight and size and have distinguishing characteristics.
Figure 1-2 shows the three atoms that make up a molecule of water. It consists of two hydrogen atoms and one oxygen atom. In the hydrogen atom, the nucleus contains one proton (+) whose positive charge is balanced by the negative charge of its one electron (-). In the oxygen atom, the nucleus contains eight protons whose positive charge is balanced by the negative charges of the eight electrons.
The hydrogen atom in figure 1-2 is the lightest of all atoms, with its single proton and single electron. Some of the heavier atoms (those of the heavier metals such as gold) have over 90 electrons. In the normal atom, the sum of the positive charges of the protons in the nucleus equals exactly the sum of the negative charges of the electrons. Such an atom is neutral.
Figure Atoms in a Molecule of Water.
