Download Atomic Mass Review Sheet

Atomic Mass Review Sheet
Atomic Number
The atomic number is equal to the number of protons in an atom. Each
element has a different atomic number. Do not get atomic number mixed up
with atomic mass or atomic weight. Remember it this way, the atomic number
is equal to the number of protons in an atom.
The atomic number can be found on the periodic table:
Symbol: Z
Units: none
Alternate names: proton number
Mass Number
The mass number is equal to the sum of the protons and neutrons in an atom.
Remember it this way, the mass number is equal to the total number of
protons plus neutrons. The mass number can be used to estimate atomic mass
(see atomic mass below)
The mass number is often indicated as a superscript in front of an atomic
symbol. The atomic number is sometimes written as a subscript before the
elemental symbol.
Example:
Mass number
12
6
C
Atomic number
Symbol: A
Units: none
Alternate names: atomic mass number
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Isotope
Isotopes are variations of elements that differ in the number of neutrons.
Because they differ in number of neutrons, they also differ in mass number.
Example:
12
13
12
6 C and 6 C are both isotopes of the element carbon. 6 C has 6 protons, 6
13
neutrons and a mass number of 12 (6+6 = 12). 6 C has 6 protons, 7 neutrons
and a mass number of 13 (6+7=13).
Atomic Mass
The atomic mass is simply the mass of an atom. The atomic mass of an atom is
about equal to the mass number of that atom expressed in amu.
Example:
12
6 C has a mass number of 12. Its atomic mass is 12.00 amu.
Units: atomic mass units (abbreviated u or amu)
Atomic Weight
The atomic weight is a weighted average of the isotopes of a particular
element. Remember it this way, atomic weight is a weighted average.
Units: none
Molecular Mass
The molecular mass is the mass of a molecule. It is calculated by adding
together the atomic masses in the molecule.
Units: amu
Molar Mass
The molar mass is the mass of an element or molecule present in 1 mole of the
element or molecule. Remember it this way, the molar mass is a the mass of 1
mole of an element or molecule. The molar mass of an element is equal to the
atomic weight expressed in g/mole. The molar mass of a molecule is calculated
by adding together the atomic weights of the atoms in the molecule.
Units: g/mole
www.ChemistryUnderstood.com
Chemistry made simple.
 Oz Scott Halpern 2011