Chemistry – King William High School




Foundations…
Law of conservation of mass – mass is neither
created nor destroyed
Law of definite proportions – a compound
contains the same elements in the same
proportions regardless of sample size
Law of multiple proportions – elements can
form compounds in different ratios





All matter is composed of atoms
Atoms of the same element are identical
Atoms cannot be subdivided, created or
destroyed
Atoms of different elements combine in small
whole number ratios to form compounds
In a reaction…atoms are combined,
separated or rearranged (NOT destroyed!)
 What do we still take from Dalton…
 All matter is composed of atoms
 Atoms of one element differ in
properties from atoms of another
element
Discovery of the electron  JJ
Thompson  Plum Pudding model
(electron’s = plums and protons =
pudding)
 Mass and charge of the electron 
Millikan
 Discovery of atomic nucleus 
Rutherford  Gold foil experiment
(nucleus has a dense, positive center)



Nucleus = protons and neutrons (both with
large mass)
Electrons outside the nucleus (very small
mass…but large volume)



Atomic number = the # of protons in the
nucleus (and the # of electrons in a neutral
atom)
Mass number = protons + neutrons
EX:



Same element with different number of
neutrons
Do not differ significantly in their chemical
behavior
EX:



Weighted average of the atomic masses of
the naturally occurring isotopes of an
element
The decimal # on the periodic table
EX: 105B has an abundance of 19.91% and 115B
has an abundance of 80.09%. What is the
atomic mass of boron?



Avogadro’s number = 6.02 x 1023
EX: How many moles of gold are in 5.64 x
1036 atoms of gold?
EX: How many atoms of gold are in a sample
that contains 0.259 mol?

The mass of one mole of a pure substance
EX: What is the molar mass of potassium?

EX: What is the molar mass of water?


EX: What is the mass in grams of 6.21 x 10-2
mol of sodium?

EX: How many moles of copper are present
in a 0.125 g sample?