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How Atoms Differ
Properties of Subatomic Particles
Particle
Electron
Proton
Neutron
Symbol
Location
Relative
Charge
Relative
mass
Actual
mass (g)
Chemical Symbols
Atomic Number
• the number of protons in an
atom
• Identifies element
• Symbol: Z
A
Z
X
Mass Number
• Represents the total
number of protons and
neutrons in the nucleus
• Symbol: A
Isotopes
• Variation in the number of neutrons
• Atoms that have the same number of protons
but have a different masses
• Ex: 3 isotopes of carbon:
12
6
C
13
6
C
14
6
C
Average Atomic Mass
• the weighted average of the isotopes of that element.
• Formula:
Average
Atomic
mass of
an element
=
(
%
abundance
of
Isotope #1
x
mass
of
Isotope
#1
)
+
(
%
abundance
of
Isotope #2
x
mass
of
Isotope #2
)
+
…
Example 1
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
average atomic mass of silver.
Example 2
Rubidium is a soft, silvery-white metal that has two
87
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?
Example 3
Boron has two naturally occurring isotopes. If
the abundance of 11B is 80.10% with an amu of
11.0093, find the abundance of 10B.
Ions
Variation in the number of electrons
Anion
• gain of electrons
• overall charge is negative
F
1−
Cation
• lose of electrons
• overall charge is positive
11 protons
12 neutrons
11electrons
11 protons
12 neutrons
10 electrons
Sodium atom
Sodium ion
1+
Na