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Atoms & Atomic Models

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Atomic Mass Unit (AMU)
A unit of mass that describes the mass of an atom or molecule.
average atomic mass
The average of the atomic masses for the isotopes of an element.
mass number
Sum of protons and neutrons
Basic building block of all matter.
A negatively charged subatomic particle located in the electron cloud outside the nucleus. It determines how atoms combine with other atoms.
valence electrons
an electron in the highest occupied energy level of an atom;available to be lost, gained, or shared in the formation of chemical compounds
A charged atom
thomson atomic model
plum pudding - atom was a positively charged solid mass (pudding) which has negatively charged electrons stuck to it. (plums)
Rutherford atomic model
Rutherford concluded that the atom is mostly empty space. All the positive charge and almost all of the mass are concentrated in a small region called the nucleus
Bohr atomic model
Atoms described as electrons orbiting the nucleus in well defined paths (solar system model), electrons can jump paths
modern atomic model
atom consists of a nucleus that contains protons and neutrons surrounded by an electron cloud
A Greek that stated that all matter is made up of four elements: earth, air, fire, and water.
atomic theory based on experiments: