6.2 – Atomic Theory
Science 10
Mr. Francis
 Atoms are made of component
particles called subatomic
particles: protons, neutrons, and
electrons.
 Every atom of any one element
will have the same number of
protons.
 Positive protons and neutral neutrons are found in
the nucleus, and negative electrons are arranged in
shells or orbits around the nucleus.
 There are an equal number of protons and electrons
in an atom. Ions form when the number of electrons
changes.
 The number of electrons in the outer shell
determines the properties of the element.
This one!
 Atomic number is the smaller number shown with
an element on the periodic table
 Atomic mass is the larger number shown with an
element on the periodic table
 In an atom, both the number of protons and the
number of electrons is equal to the atomic number
 To find neutrons:
 Neutrons = Atomic Mass – Atomic Number
 We can show a particular atom in the form: Ag – 107
 The symbol, Ag tells us what the element is (Silver)
 We can refer to the periodic table to determine the
atomic number which tells us the number of protons and
electrons
 107 is the atomic mass of this specific element of Silver
 Even though the periodic table tells you that the atomic
mass of silver is 107.9, that mass is an average of all
known isotopes of Silver
Assignment
 Atomic Theory Worksheet
 P. 156 # 2, 3a,c,e, 4, 5, 7