How Atoms Differ
I.
Particle
Properties of Subatomic
Particles
Symbol
e- or
Electron
0e
1
p+ or
Proton
1p
1
n0 or
Neutron
1n
0
Location
In the space
surrounding
the nucleus
In the
nucleus
In the
nucleus
Relative
Charge
Relative
mass
Actual
mass (g)
1-
1
1840
9.11
x 10-28
1
1.673
x 10-24
1
1.675
x 10-24
1+
0
II. Atomic Number
• the number of protons in an atom
• Identifies element
– each atom has unique #
– # never changes
III. Mass Number
• represents the total number of protons and
neutrons in the nucleus
• # of neutrons = mass number – atomic
number
IV. Isotopes
• Atoms of the same element but have a
different # of neutrons
• Ex: 3 isotopes of carbon:
• All elements have isotopes (some 2, some 3,
etc.)
• Some isotopes are naturally radioactive.
• Ex: Plutonium
V. Representing Isotopes
• In Ag-107, the 107 represents the mass number
(neutrons + protons)
• the 47 represents the number of protons
Practice:
1. What is the mass number for Co-59? 59
2. What is the mass number for
7
VI. Atomic Mass
• The standard is the atomic mass unit (amu): defined
as 1/12 of the mass of a carbon-12 atom
• the weighted average of the isotopes of that
element.
• Formula:
Atomic
mass of
an
element
=
%
abundance
(
of
Isotope #1
x
mass
of
Isotope
#1
)
+
%
abundance
(
of
Isotope #2
x
mass
of
)
Isotope #2
+
…
Practice 3
• Silver has two naturally occurring isotopes.
Ag-107 has an abundance of 51.82% and mass of
106.9 amu.
Ag-109 has a relative abundance of 48.18% and a
mass of 108.9 amu.
Calculate the atomic mass of silver.
Practice 4
• Rubidium is a soft, silvery-white metal that
87
has two common isotopes, 85
Rb
and
Rb.
37
37
If the abundance of 85Rb is 72.2% and the
abundance of 87Rb is 27.8%, what is the
average atomic mass of rubidium?
Vocabulary to Know
• Atomic #- same # of protons & electrons
• Mass #-protons + neutrons
14
written 2 ways: Carbon-14 or 6 C
• Isotopes-same # of protons, different # of
neutrons
• Atomic mass-weighted average mass