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Current understanding of the atom

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• The nucleus of an atom is extremely small even though it contains almost all the mass of an atom.
• Atomic number (or proton number) = the number of protons in an atom (also the same number of electrons)
• Mass number (or nucleon number) = the mass of an atom
• Electron configuration : shows the number of electrons in each shell - first shell contains a maximum of 2 electrons, second and third shell have a maximum of 8 electrons.
• Group number = number of outer-shell electrons
• Period number = number of shells of electrons
• Atoms are neutral because they have the same number of protons and electrons
• Some atoms lose or gain electrons so that they have a full outer shell of electrons and gain noble gas stability. They are then positively or negatively charged ions
• A positive ion is called a cation (pawsitive :))
• A negative ion is called an anion ( nobody likes onions)
• Bildunterschrift: Atoms are made from three subatomic particles:

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