Remember from Chemistry:
• Mass numberMass number: the number of protons + number of neutrons
• Atomic numberAtomic number: the number of protons in an atom of an element.
• Isotopes:Isotopes: atoms of the same elements that have a different number of neutrons and therefore a different mass number
There are many isotopes of carbon.
• For example: carbon-12, carbon-13 andcarbon-14
• How many protons in each of these atoms of carbon? – 6
• How many neutrons in each of these atoms of carbon?
• Carbon-12 = ____ neutrons• Carbon-13 = ____ neutrons• Carbon-14 = ____ neutrons
Standard Atomic Notation
• Carbon-12 = 12 C
6
• Carbon-13 = _____
• Carbon-14 = _____
Mass number
Atomic number
Isotopes of Hydrogen
• Hydrogen: 1 proton and 0 neutrons
• Deuterium: 1 proton and 1 neutron
• Tritium: 1 proton and 2 neutrons
Radioactive Decay:
• The nuclei of some isotopes are stable, whereas, others are not.
• In unstable nuclei, the nuclear force is not enough to overcome the repulsive electrical forces with in the nucleus.
• As a result the nuclei are radioactive.
• When an unstable nucleus emits radiation, it undergoes a radioactive decay
Types of radioactive decay
• Alpha Decay:Alpha Decay:• Particle emitted: Helium nucleus• Result: Atom with two fewer protons and
neutrons Sample Equations:Parent isotope Daughter isotope
• U → _____ + He
• U → Th + _____
Types of radioactive decay
• BetaBeta• Particle emitted: Electron• Result: # of neutrons decrease by one and the #
of protons increase by one = new element
Sample Equations:Parent isotope Daughter isotope
• C → ____ + e
• C → N + ____
• GammaGamma• Particle emitted: No particle, but gives off
excess energy• Result: No change to type of nucleus, it just has
less energy. Sample Equations:Parent isotope Daughter isotope
• Ba → _____ + Gamma radiation
• Ba → Ba + ______
Types of radioactive decay
On your data sheets: p12
Assignment:• Fill in the 7.1 worksheets p123-5 (all) and
p126 (pick two alpha, two beta and two gamma questions)
• You are going to have to look up some of this information in your textbook
• Quiz next class– Identifying and completing decay equations– Given # of neutrons and number of protons
can you determine, mass #, atomic #, the element, isotope name and isotope symbol.
Half Life
Section 7.2
PLO: Unit 2 #5.2
Half Life:
• Half Life: The time required for half the nuclei of a sample of a radioactive isotope to decay.
• The half life is the same regardless of the starting amount of the isotope.
• Because the amount of all radioactive isotopes decrease by half in each half life, graphs that show the amounts of these isotopes at various times look similar.
• The only difference is the time scale for decrease.
Examples of half life:carbon
020406080
100120
0 20000 40000 60000 80000
Time (Years)
amo
un
t o
f sa
mp
le
left carbon
Uranium
0100200300400500600
0 50000 100000 150000
Time (years)
sam
ple
of
ura
niu
m
Uranium
Half Life Problems
• Figure out what the problem is asking you to find.
• Fill in the table with the information given to you in the problem.
Half Life Table for Solving Word Problems
Time # of Half lives Amount of parent isotope
** optional ** Amount of daughter isotope
0 0 Original Amount 0
1
2
3
4
Homework:
• Fill in the 7.2 worksheets p134 (odd) and 135
• For p 134 you must show the half life tables
Half Life Table for Solving Word Problems
Time # of Half lives Amount of parent isotope
** optional ** Amount of daughter isotope
0 0 Original Amount 0
1
2
3
4