Counting Atoms

Counting Atoms

1. Average Atomic Mass

   • The weighted average of the atomic masses of the naturally occuring isotopes of an element.

2. Mass Number

   • The total number of protons and neutrons that make up the nucleus of an isotope.

3. Atomic Number

   • The number of protons in each atom of an element.

4. Isotopes

   • Are atoms of the same element that have different masses, do not differ notably in their chemical behavior.
   • Isotopes of a particular element have the same number of protons and electrons but different number of neutrons.
   • Scientists can determine where some elements come from by measuring the percentage of isotopes.

5. Vocabulary

   • Nuclide: Is a general term for a specific isotope of an element.
   • Mole: The amount of a substance that contains as many particles as there are atoms.
   • Molar Mass: The mass of one mole of a pure substance.
   • One Urified Atomic Mass: Or 1 u, is exactly 1/12 of the mass of a carbon-12 atom.
   • Avogrado's Number: Is the number of particles in exactly one mole of a pure substance.
     • Can be used to find the number of atoms of an element from the amount in moles or to find the amount of an element in moles from the number of atoms.