Difference between revisions of "Atom"

Revision as of 23:04, November 12, 2007

Subatomic resolution of atoms by AFM

An atom is a particle of matter indivisible by chemical means. ^[1] The word atom comes from the Greek term for indivisible, átomos.

Structure

Atoms are comprised of three subatomic particles: positively charged protons, electrically neutral neutrons and negatively charged electrons. Protons and neutrons are comprised of quarks and are contained in close proximity in the center of an atom, forming the nucleus. Electrons inhabit the space around the nucleus, and are arranged around it in a series of layers, known as shells or energy levels. Currently quarks and electrons are considered truly elementary particles, though neither are capable of being seen.

Those who understand electrical theory might notice that positively charged particles packed closely together would repel one another. The nucleus stays together because of what is known as the strong nuclear force. The quantization of this force is a tiny particle called a "gluon".

Atomic Number

Isotopes

Chemical elements are made up of atoms with certain properties. The number of protons in the nucleus of an atom (known as the atomic number) determine the properties of the atom, and the element it constitutes. For example, Hydrogen has one proton, and therefore an atomic number of 1. Oxygen has 8 protons in its nucleus and has an atomic number of 8. Under normal conditions, atoms contain an equal number of protons and electrons.

Ions

Atoms are normally electrically neutral; they have no charge. However, electrons in the valence shell can be gained or lost (depending on the element and the conditions) to form an ion. An atom that loses electrons becomes positively charged and is known as a cation. An atom that gains electrons electrons becomes negatively charged and is known as an anion.

Many common substances are made up of ions. For example, sodium chloride (NaCl), otherwise known as table salt, is made up of sodium cations (Na⁺) and chlorine anions (Cl^-) in equal proportions. The negatively charged chlorine ions are attracted to the positively charged sodium ions, forming an ionic bond. This results in a lattice structure, which is responsible for sodium chloride being crystalline in its solid state.

Isotopes

Atoms of the same element that have different numbers of neutrons are known as isotopes. Some isotopes are more stable than others, and occur more often in nature, but there is no "standard" number of neutrons in a given element. The atomic weight of an element is a weighted average of the number of neutrons and protons (number of protons remains constant in a given element) in all naturally occurring isotopes.

References

1. ↑ Glossary of Nuclear Terms