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Atom: The smallest indivisible particle of matter that can have an independent existence.

Atomic Mass Unit: A unit of mass equal to 1/12 the mass of a carbon-12 nucleus, which is 1.660 538 73 × 10-27 kg ± 0.000 000 13 × 10-27 kg [1998 CODATA values]. Abbreviated as amu or u. Sometimes called the d . . . View Full Definition

Atomic Nucleus: A tiny, incredibly dense positively charged mass at the heart of the atom. The nucleus is composed of protons and neutrons (and other particles). It contains almost all of the mass of the at . . . View Full Definition

Atomic Number (Z): The number of protons in an atomic nucleus. The atomic number and the element symbol are two alternate ways to label an element. In nuclide symbols, the atomic number is a leading subscript; . . . View Full Definition

Atomic Orbital: A wavefunction that describes the behavior of an electron in an atom.

Anatomy: The study of form. Gross anatomy involves structures that can be seen with the naked eye. It is as opposed to microscopic anatomy (or histology) which involves structures seen under the micr . . . View Full Definition

Subatomic Particles: The three kinds of particles that make up atoms: protons, neutrons, and electrons.

Spring Diatom Increase: The major rapid population increase of diatoms, occurring in the spring in temperate-boreal latitudes

Atomic Radius: One half the distance between nuclei of atoms of the same element, when the atoms are bound by a single covalent bond or are in a metallic crystal. The radius of atoms obtained from covalent . . . View Full Definition

Atomic Mass: The mass of an atom is primarily determined by the number of protons and neutrons in its nucleus. Atomic mass is measured in Atomic Mass Units (amu) which are scaled relative to carbon, 12C, . . . View Full Definition