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

$A = Z + N$

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.