Atoms

Atoms

1. smallest particle on an element with all of the properties of the element

2. Atomic Number =“Z”

   • identifies the element
     • number of protons in the nucleus (always a whole, counting number)

3. Mass Number

   • the total number of protons and neutrons in an atom of an element; written following the chemical symbol
     • Example: C-12 has a total of 12 protons and neutrons

4. Atomic Mass Unit (amu)

   • by definition 1/12 of the mass of a C-12 atom

5. Atomic Mass

   • the weighted average of the isotopes of an element; most elements have 2 or more isotopes in nature
     • The average atomic mass of an element is often close to the mass of the most abundant isotope

6. Isotopes

   • atoms that have the same number of protons but a different number of neutrons
   • they are atoms of the same element with different mass numbers