Thursday, July 5
• Section 3.8, 4.1 – 4.2
• Valence Electrons (and review for the exam)
• Natural Radioactivity
• Nuclear Reactions
– Suggested Book Questions (Red indicates those covered in this lecture): • CHAPTER 4 ‐ 4.1: 1‐11 ODDS; 4.2: 13‐21 ODDS; 4.3: 23,25,27; 4.4: 29,31,33; 4.5: 35,37; EOC: 45‐81 ODDS
• ALEKS Objective #1 Due TODAY, July 5th at 10:00PM
• Exam 1 is tomorrow, July 6th. Valence Electrons
• Outer shell electrons.
• Participate in bonding (Chapter 5).
• Easy to know from electron configuration or reading the periodic table.
• Electron dot diagram... Let’s do some examples.
Periodic Trends
• Which elements lose electrons, which elements gain electrons?
• Metals ______________________________
• Non‐metals __________________________
• Why? Let’s do a couple examples...
Atomic Symbol Review
Atomic Symbol
A
X
Z
A: Mass number
Z: Atomic number
X: Chemical Symbol
• It is important to be able to think about the meaning behind the atomic symbols for Chapter 3 and 4. Radioactive Particles
Alpha Particle
Beta Particle
Positron
Gamma Particle
Radioactive Isotopes
Elements with Z ≥ ______ usually have one or more radioactive isotopes.
A _________________________has an unstable nucleus due to proton‐
proton repulsion and will emit radiation to become more stable.
Common types of radioactive decay:
Alpha () – He nucleus (2 protons + 2 neutrons) released from the nucleus. Beta () – e– released from a neutron.
Positron () – positively‐charged electron released from a proton.
Gamma () – energy released when nucleus rearranges itself.
Radioactive decay often results in a change in atomic number.
alpha particle
beta particle
positron
Different levels of protection are required for each radiation type.
5
Buddy Quiz
• If radioactive decay results in a change in atomic number, what does that mean? Alpha Decay
When a radioactive nucleus emits an alpha particle, a new nucleus forms that has
 a mass number 4 less than that of the initial nucleus  an atomic number that has decreased by 2 from that of the initial nucleus
In a balanced alpha‐decay equation, the sums of the mass and atomic numbers on both sides of the arrow are equal.
251
98
Cf 
247
96
4
2
Cm + He
7
Alpha Decay Example
Write an equation for the alpha decay of 222Rn.
222
86
 ? +
Rn
4
2
He
Determine the mass number:
Determine the atomic number: A = 222 – 4 = 218
Z = 86 – 2 = 84
Determine the symbol of element:
84 = Po
Complete the equation:
222
86
Rn

218
84
Po +
4
2
He
84
Po
85
At
86
Rn
4
2
He
8
Beta Decay
A beta particle is emitted when a neutron in the nucleus breaks down:
1
0
n

0
-1
e +
1
1
H
The mass number of the atom is unchanged, but the atomic number increases by 1.
131
53
I 
0
1
e +
131
54
Xe
9
Example of Beta Decay
Write an equation for the decay of K42 (potassium‐42), a beta emitter.
42
19
K  ? +
0
-1
e
Mass number: (same) = 42
Atomic number: 19 + 1 = 20
Symbol of element: 20 = Ca
Complete the equation:
42
19
K 
42
20
Ca +
0
-1
e
0
-1
e
19
K
20
Ca
10
Example
Write the nuclear equation for the beta decay of Co‐60.
11
Example
What radioactive isotope is produced when a neutron bombards 59Co?
59
27
Co + n  ? + He
1
0
4
2
12
Positron Emission
In positron emission,
 a proton is converted to a neutron and a positron
1
1
H 
1
0
n +
0
+1

0
-1
e +
1
1
1
0
n
e
H
 the mass number of the new nucleus is the same, but the atomic number decreases by 1
49
25
Mn 
49
24
Cr +
0
+1
e
13
Gamma Radiation
In gamma radiation,
 energy is emitted from an unstable nucleus, indicated by m following the mass number
 the mass number and the atomic number of the new nucleus are:
14
Summary of Types of Radiation
15