1. Atom
   An atom is a microscopic structure found in all ordinary matter around us
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2. Atomic mass
   In reference to a certain isotope of a chemical element, atomic mass is the mass of one atom of the isotope expressed in units
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3. Atomic number
   The atomic number (Z) is a term used in chemistry and physics to represent the number of protons found in the nucleus of an atom
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4. Chemical element
   A chemical element, often called simply element, is a substance that cannot be divided or changed into different substances by ordinary chemical methods
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5. Electron
   The electron is a subatomic particle. In an atom the electrons surround the nucleus of protons and neutrons..
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6. Neutron
   In physics, the neutron is a subatomic particle with no net electric charge
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7. Proton
   In physics, the proton is a subatomic particle with an electric charge of one positive
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