Counting Atoms

Counting Atoms

1. Average atomic mass is a weighted value

   • Average Atomic Mass is the weighted average of the atomic masses of the naturally occurring isotopes of an element
   • Different samples of the same element can differ in the relative abundance of isotopes.
   • Unlike atomic numbers, the average atomic mass is a statistical calculation.

2. A relative mass scale makes counting atoms possible

   • The relative atomic mass scale makes it possible to know-how many atoms of an element are presented in a sample of the element with a measurable mass.
   • Avogadro's number
     • 6.02 x 1023, the number of atoms or molecules in 1 mol
       • The number of particles in a mole is known as Avogadro's number is named for the nineteenth-century Italian scientist Amedeo.
     • Mole
       • The SI base unit used to measure the amount of a substance whose number of particles is the same as the number of atoms of carbon in exactly 12g of carbon 12
         • The molde is a counting unit, just like a dozen is.
     • Molar Mass
       • The mass in grams of 1 mol of a substance
         • Is the amount of substance that contains Avogadro's numbers of particles.

3. ATOMS-NEUTRONS

   • All atoms of an element must have the same number of protons but not neutrons.
     • Atomic Number
       • The number of protons in the nucleus of an atom.
       • Isotopes
         • Are atoms of the same element that have different masses
         • Mass Number
           • Is the total number of protons and neutrons that make up the nucleus of an isotope.
           • Nuclide
             • It is a general term for a specific isotope of an element.
   • Atomic Mass is a Relative Measure
     • Unified atomic mass unit- 1u, is exactly 1/12 the mass of a carbon-12 atom. The atomic mass of another atom is determined by comparing it with the mass of carbon -12 atom