Download Atomic mass unit (AMU) The masses of protons and neutrons are

Atomic mass unit (AMU)
The masses of protons and neutrons are nearly equal (1.0073 and 1.0087 amu respectively).
Avogadro’s Number and the mole
A mole is the amount of matter that contains as many objects (atoms, molecules, or other objects) as
the number of atoms in 12 grams of 12 C . This number has been determined through experimentation
to be 6.022 ! 10 23 , and is known as Avogadro’s number.
A mole of atoms, a mole of molecules, or a mole of anything all contain Avogadro’s number of these
objects:
1 mol 12C atoms = 6.022 ! 10 23 12C atoms
1 mol H 2O molecules = 6.022 ! 10 23 H 2O molecules
Ex: Convert 1.8 ! 10 –11
J
J
to
, where U = Uranium.
U nucleus
mole of U
%
J
J
"
%"
–11
23 U nuclei
13
$# 1.8 ! 10 1 U nucleus '& $ 6.022 ! 10 mole of U ' = 1.08 ! 10 mole of U
#
&
The mass of a single atom of an element [amu] is numerically equal to the mass [g] of 1 mol of that
element, regardless of the element.
1 atom of
12
C has a mass of 12 amu ! 1 mol
12
C has a mass of 12 g.
Molar mass
The molar mass of an element is the atomic weight in grams per mole, i.e. the molar mass [g/mol] of
any substance is always numerically equal to its formula weight [amu]
e.g.
1 H2O molecule has a mass of 18.0 amu ↔ 1 mol H2O has a mass of 18.0 g
1 O2 molecule has a mass of 16.0 amu ↔ 1 mol O2 has a mass of 16.0 g
Q: How many moles of water are in a liter of water, if 1 liter = 1 kilogram water.
A: Atomic weights:
Hydrogen: 1.008 amu
Oxygen: 16.00 amu
Formula weight = 1.008 amu + 1.008 amu + 16.00 amu = 18.016 amu
! 1 mol $
1000 g #
= 55.55 moles of water
" 18.0 g &%
References
Chemistry, the Central Science. Brown et al., Pearson