Chapter 7 Lesson 2Chapter 7 Lesson 2Isotopes and RadioactivityIsotopes and Radioactivity
What’s the What’s the difference difference between the two between the two atoms in Figure atoms in Figure 12?12?
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Isotopes – Different Isotopes – Different Numbers of NeutronsNumbers of Neutrons
What’s the difference What’s the difference between the two between the two atoms in Figure 12?atoms in Figure 12?
O-17 has O-17 has one extra one extra neutronneutron
These two These two atoms are atoms are called called IsotopesIsotopes
How Many Neutrons?How Many Neutrons?
Isotopes with more neutrons are Isotopes with more neutrons are heavier than isotopes with fewer heavier than isotopes with fewer neutrons.neutrons.
Lets calculate the number of neutrons Lets calculate the number of neutrons in a Carbon-14 atom:in a Carbon-14 atom:
How many neutrons?How many neutrons?
How many neutrons are in Carbon-12 How many neutrons are in Carbon-12 atoms?atoms?
How many neutrons are in Carbon-13 How many neutrons are in Carbon-13 atoms?atoms?
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How many neutrons?How many neutrons?
How many neutrons are in Carbon-12 How many neutrons are in Carbon-12 atoms?atoms?
12 – 6 = 6 neutrons12 – 6 = 6 neutrons
How many neutrons are in Carbon-13 How many neutrons are in Carbon-13 atoms?atoms?
13 – 6 = 7 neutrons13 – 6 = 7 neutrons
What determines What determines properties?properties?
Chemical properties are determined by Chemical properties are determined by the number of valence electrons an the number of valence electrons an atom has.atom has.
Valence electrons determine what type Valence electrons determine what type of bond an element will form.of bond an element will form.
Do isotopes have similar chemical Do isotopes have similar chemical properties??properties??
What determines What determines properties?properties?
Chemical properties are determined by Chemical properties are determined by the number of valence electrons an atom the number of valence electrons an atom has.has.
Valence electrons determine what type Valence electrons determine what type of bond an element will form.of bond an element will form.
Do isotopes have similar chemical Do isotopes have similar chemical properties??properties??
Yes they do, because they have the same Yes they do, because they have the same number of electrons.number of electrons.
What is radioactive decay?What is radioactive decay?
The three isotopes of Carbon have The three isotopes of Carbon have similar properties, but C-14 is similar properties, but C-14 is radioactive.radioactive.
What is radioactive decay?What is radioactive decay?
When radioactive decay occurs, an When radioactive decay occurs, an unstable atomic nucleus changes into unstable atomic nucleus changes into another nucleus by releasing one or more another nucleus by releasing one or more particles and energy.particles and energy.
Stability increases and a different element Stability increases and a different element is formed. (See Figure 15 on page 303)is formed. (See Figure 15 on page 303)
Uses of Radioactive DecayUses of Radioactive Decay
Look on page 304 at the bottom.Look on page 304 at the bottom.
List 3 ways that we have found to use List 3 ways that we have found to use radioactive decayradioactive decay
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Uses of Radioactive DecayUses of Radioactive Decay
Look on page 304 at the bottom.Look on page 304 at the bottom.
List 3 ways that we have found to use List 3 ways that we have found to use radioactive decay:radioactive decay:1.1. Medical imagingMedical imaging
2.2. Detection of cancer cellsDetection of cancer cells
3.3. Killing of cancer cellsKilling of cancer cells
4.4. Preservation of foodPreservation of food
Radioactive Elements and Radioactive Elements and the Periodic Tablethe Periodic Table
Radioactive elements = elements that Radioactive elements = elements that have only radioactive isotopeshave only radioactive isotopes
Radioactive Elements are HEAVY so Radioactive Elements are HEAVY so they are found near the bottom of the they are found near the bottom of the periodic table (See figure 18 below)periodic table (See figure 18 below)
Half-lifeHalf-life
Isotopes decay at very Isotopes decay at very different ratesdifferent rates
Half-life= the time it Half-life= the time it takes for half of the takes for half of the original sample to original sample to decaydecay
Uranium-235 has a Uranium-235 has a half life of 713 million half life of 713 million years!years!
How many grams How many grams would be left after would be left after another 713 million another 713 million years?years?
Half-lifeHalf-life
Erbium has many isotopes:Erbium has many isotopes:
1. How many seconds is the 1. How many seconds is the half-life for Er-147?half-life for Er-147?
2. How much time would it take 2. How much time would it take for a 100g sample of Er-145 to for a 100g sample of Er-145 to decay to a 25g sample?decay to a 25g sample?
3. How much time would it take 3. How much time would it take for a 200g sample of Er-169 to for a 200g sample of Er-169 to decay to a 100g sample? 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
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Half-lifeHalf-life
Erbium has many isotopes:Erbium has many isotopes:
1. How many seconds is the half-1. How many seconds is the half-life for Er-147? 2.5 slife for Er-147? 2.5 s
2. How much time would it take for 2. How much time would it take for a 100g sample of Er-145 to decay a 100g sample of Er-145 to decay to a 25g sample? (0.9 +0.9 = 1.8 to a 25g sample? (0.9 +0.9 = 1.8 s)s)
3. How much time would it take for 3. How much time would it take for a 200g sample of Er-169 to decay a 200g sample of Er-169 to decay to a 100g sample? 9.40 daysto 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
