Atom (science)

An atom (from the Greek atomos, indivisible) is the smallest physical unit that can retain its chemical properties. While atoms were once thought to be the smallest instances of mass in the universe, we now know that they are made up of smaller subatomic-particles.

Structure of the Atom

Atoms are made of a dense nucleus formed by the two nucleons (positively charged protons and zero charge neutrons and surrounded by a much larger "cloud" of electrons. The number of protons contained in the nucleus determines the atomic number of the atom and in turn what element it is classified as. The number of neutrons further specifies the isotope number of that element.

The nucleus of an atom is held together by the residual strong force despite its significant positive charge. The electrons which surround the atom are electromagnetism attracted to the nucleus due to their negative charge.

Most combinations of nucleons are inherently unstable and undergo a number of radiation in order to form more stable nuclei.

• Alpha decay
• Beta+ decay
• Beta- decay
• Gamma decay

See Also

• Element