Law of the conservation of mass

the mass of the products (overall) always equals the mass of the reacting substances

A Graphic of the Atom

Atomic number and Mass Number

Atomic Number and Mass Number

• Atomic Number (Z)
  • the number of protons in the nucleus of an element's atom
  • is generally found on the periodic table above the elemental symbol
• Mass Number (A)
  -the number of protons and neutrons in the nucleus of an element's atom
  is generally found below the elemental symbol on the periodic table

  $A = Z + N$

• Neutron Number (N)
  • the number of neutrons in the nucleus of an element's atom

An isotope of an element is an atom that contains a specific number of neutrons.

Isotopes, Hydrogen, Deuterium, and Tritium

An atomic mass unit (amu) is equal to 1/12 the mass of a carbon-12 atom.