2. 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.

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

4. Symbols of Elements – nuclear  General format for identifying a particular nuclide

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

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

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

8. Symbols of Elements 12 C Nuclear SymbolHyphen notation Carbon-12

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

10. Atomic Mass

11. 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

12. 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