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 $${.box .has-text-centered} <figure style='float: right'> <img src='https://shaunmwilliams.com/IntroChem/figures/chapter2/Picture7.jpg' alt='Isotopes' width='300' height='300' /> <figcaption>Hydrogen isotopes</figcaption> </figure> An [isotope](https://shaunmwilliams.com/IntroChem/lecture2.html#slide-15) of an element is an atom that contains a specific number of neutrons. Isotopes, Hydrogen, Deuterium, and Tritium An [atomic mass](https://shaunmwilliams.com/IntroChem/lecture2.html#slide-19) unit (amu) is equal to 1/12 the mass of a carbon-12 atom.