The atom is a basic unit of matter, consisting of a central nucleus (containing positively charged protons and electrically neutral neutrons), and surrounded by negatively charged electrons which move in 1 or more orbital “shells” around the nucleus.
For example, consider a carbon atom:
The number of protons in a nucleus is the atomic number, and defines the type of element the atom forms. Thus, carbon has an atomic number of 6.The number of neutrons in a nucleus determines the isotope of an element. For example, carbon-12 has 6 protons and 6 neutrons, while carbon-14 has 6 protons and 8 neutrons.
Most matter is said to be electrically “neutral”, since the #electrons = #protons. (Ions are atoms which are not neutral – ie, they have either gained or lost electrons).
An atom may have multiple electron “orbital shells”. In the case of carbon, the first shell contains 2 electrons, and the second shell contains 4 electrons.
A group of atoms may remain “bound” to each other, forming a molecule.
Electrical Stability
If an atom has multiple electron orbital shells, the outermost shell can have a maximum of 8 electrons. The actual number of electrons in the outer shell determines how electrically “stable” the atom is. Any atom with only 1 electron in the outer shell is electrically “unstable”. This electron (known as a “free electron”) can move easily from one atom to another at random, and is characteristic of metals that are good conductors of electricity.
Conductors are materials made from elements (usually metals) with free electrons. For example,
- Copper (Cu) has 4 shells, with 2 + 8 + 18 + 1 = 29 electrons.
- Silver (Ag) has 5 shells, with 2 + 8 + 18 + 18 + 1 = 47 electrons.
- Gold (Au) has 6 shells, with 2 + 8 + 18 + 32 + 18 + 1 = 79 electrons
Semi-conductors are materials whose conductivity is somewhere between conductors and insulators. Examples are carbon, germanium, and silicon. These materials are used to make transistors and other electronic components.
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