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| Ancient Greek philosopher who came up with the idea of the atom. Atom comes from the Greek atomos meaning indivisible. |
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| Ancient Greek philosopher who disagreed with Democritus and said that matter was infinitely divisible. |
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| English Schoolteacher and chemist who revived the idea of the atom in the early 1800's and made five important statements in his atomic theory. |
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| English physicist who worked with cathode rays and discovered these rays had a negative charge and contained particles traveling at a high rate of speed. The particles in these cathode rays were later named electrons. |
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| American physicist who carried out an oil drop experiment to find the charge to mass ratio of an electron. The results of this experiment showed that the mass of an electron is approximately 2000 times smaller than a hydrogen atom. Despite its small size, the electron has a negative charge equal in magnitude to the positive charge on a proton. |
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| Physicist from New Zealand who performed the gold foil experiment in 1911. This experiment led to a new atomic model that included a densely packed positively charged nucleus, electrons orbiting the nucleus, and large amounts of empty space in between. |
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| Japanese physicist who suggests that an atom has a central nucleus. His idea is confirmed by the gold foil experiment performed by other scientists. |
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| Danish physicist who suggests that electrons move in circular orbits at fixed distances from the nucleus. |
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| Austrian physicist who developed mathematical equations to describe the motion of electrons in atoms. His work led to the electron cloud model |
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| French physicist who proposed that particles like electrons have some properties of waves. |
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| English physicist who confirmed the existence of neutrons, which have no charge and are contained in the nucleus of atoms. |
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| Negatively charged particle that orbits the nucleus. Its mass is 1/1836 of an amu. |
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| Positively charged particle located in the nucleus, with a mass of approximately 1 amu. |
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| Neutrally charged particle found in the nucleus with no charge. |
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| The number of protons in the nucleus of a particular element. |
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| The number of protons and neutrons added together. |
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| The weighted average of the masses of all the isotopes of an element. |
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| A unit of mass equal to one-twelfth of the mass of a carbon-12 atom. |
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| an atom or group of atoms that has a positive of negative charge. |
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| An atom or group of atoms with a positive charge. |
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| An atom or group of atoms with a negative charge. |
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| The tiny, dense central portion of an atom, composed of protons and neutrons. |
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| Atom of the same element that have the same atomic number but different mass numbers due to a different number of neutrons. |
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