Chapter 7 Lesson 2
Isotopes and Radioactivity
Left
What’s the difference
between the two atoms
in Figure 12?
Isotopes – Different Numbers of
Neutrons
What’s the difference
between the two atoms
in Figure 12?
O-17 has one
extra neutron
These two
atoms are
called
Isotopes
How Many Neutrons?
Isotopes with more neutrons are heavier than
isotopes with fewer neutrons.
Lets calculate the number of neutrons in a Carbon-14
atom:
Left
How many neutrons?
How many neutrons are in Carbon-12 atoms?
How many neutrons are in Carbon-13 atoms?
How many neutrons?
How many neutrons are in Carbon-12 atoms?
12 – 6 = 6 neutrons
How many neutrons are in Carbon-13 atoms?
13 – 6 = 7 neutrons
What determines properties?
Chemical properties are determined by the number
of valence electrons an atom has.
Valence electrons determine what type of bond an
element will form.
Do isotopes have similar chemical properties??
What determines properties?
Chemical properties are determined by the number
of valence electrons an atom has.
Valence electrons determine what type of bond an
element will form.
Do isotopes have similar chemical properties??
Yes they do, because they have the same number of
electrons.
What is radioactive decay?
The three isotopes of Carbon have similar properties,
but C-14 is radioactive.
What is radioactive decay?
When radioactive decay occurs, an unstable atomic
nucleus changes into another nucleus by releasing
one or more particles and energy.
Stability increases and a different element is formed.
(See Figure 15 on page 303)
Left
Uses of Radioactive Decay
Look on page 304 at the bottom.
List 3 ways that we have found to use radioactive
decay
Uses of Radioactive Decay
Look on page 304 at the bottom.
List 3 ways that we have found to use radioactive
decay:
1.
2.
3.
4.
Medical imaging
Detection of cancer cells
Killing of cancer cells
Preservation of food
Radioactive Elements and the
Periodic Table
Radioactive elements = elements that have only
radioactive isotopes
Radioactive Elements are HEAVY so they are found
near the bottom of the periodic table (See figure 18
below)
Half-life
Isotopes decay at very
different rates
Half-life= the time it
takes for half of the
original sample to decay
Uranium-235 has a half
life of 713 million years!
How many grams would
be left after another 713
million years?
Left
Half-life
Erbium has many isotopes:
1. How many seconds is the half-life for
Er-147?
2. How much time would it take for a
100g sample of Er-145 to decay to a
25g sample?
3. How much time would it take for a
200g sample of Er-169 to decay to a
100g sample?
Half-Lives of Erbium
Isotope
Half-Life
Er-145
0.9 s
Er-147
2.5 s
Er-154
3.73 min
Er-156
19.5 min
Er-158
2.29 h
Er-169
9.40 days
Half-life
Erbium has many isotopes:
1. How many seconds is the half-life for
Er-147? 2.5 s
2. How much time would it take for a
100g sample of Er-145 to decay to a
25g sample? (0.9 +0.9 = 1.8 s)
3. How much time would it take for a
200g sample of Er-169 to decay to a
100g sample? 9.40 days
Half-Lives of Erbium
Isotope
Half-Life
Er-145
0.9 s
Er-147
2.5 s
Er-154
3.73 min
Er-156
19.5 min
Er-158
2.29 h
Er-169
9.40 days