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Subatomic Particles Protons and electrons are the only particles that have a charge. Protons and neutrons have essentially the same mass. The mass of an electron is so small we ignore it.

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Isotopes Isotopes are atoms of the same element with different masses. Isotopes have different numbers of neutrons.

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Symbols of Elements nuclear General format for identifying a particular nuclide

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Symbols of Elements Elements are symbolized by one or two letters.

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Symbols of Elements All atoms of the same element have the same number of protons, which is called the atomic number, Z.

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Symbols of Elements The mass of an atom in atomic mass units (amu) is the total number of protons and neutrons in the atom.

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Symbols of Elements 12 C Nuclear SymbolHyphen notation Carbon-12

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Atomic Mass Atomic and molecular masses can be measured with great accuracy using a mass spectrometer.

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Atomic Mass

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Average Mass Because in the real world we use large amounts of atoms and molecules, we use average masses in calculations. IsotopeMass (amu)Natural abundance (%) Neon-2019.992490.4838 Neon-2120.99400.2696 Neon-2221.99149.2465

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Average Mass Average mass is calculated from the isotopes of an element weighted by their relative abundances. IsotopeMass (amu)Natural abundance (%) Neon-2019.992490.4838 Neon-2120.99400.2696 Neon-2221.99149.2465