Key to In-Class Group Activity #2 (Chem 101, Summer 2006)
Name _____________KEY___________________
1. Give the name of each of the elements with the following symbols:
a) Br _____Bromine________
b) K _______Potassium_______
c) Ag _____Silver_______
d) S _______Sulfur_______
2. Give three common properties of metals:
Metals are typically shiny, ductile/malleable and good conductors of heat/electricity.
(Also, metals usually have relatively high melting points and densities.)
3. a) Which group in the periodic table contains only nonmetals?
Group 8A
b) Which period in the periodic table contains only nonmetals?
Period 1
4. If an element has atomic number 17 and mass number 35,
a) What is the element?
Chlorine
b) How many protons does it have?
17 protons
c) How many neutrons does it have?
18 neutrons
d) How many electrons does it have?
17 electrons
5. Copper has two naturally occurring isotopes: copper-63 (69.17%) and copper-65
(30.83%). Calculate the approximate atomic mass of copper.
(0.6917 x 63 amu) + (0.3083 x 65 amu) = 63.62 amu
6. Which isotope is produced when krypton-81 undergoes beta decay?
reaction.
81
36 Kr
81
37 Rb
+
0
-1
Write the
e
7. By what process does thorium-230 decay to radium-226? Write the reaction.
Alpha decay:
230
90
Th
226
88
Ra
+
4
2
He
8. The half-life of 32P is about 14 days.
a) Approximately how much activity will be left in a sample of
activity of 25 mCi after 42 days?
32P
with an initial
42 days = 3 x 14 days = 3 half-lifes
25 mCi/2 = 12.5 mCi
12.5 mCi/2 = 6.25 mCi
6.25 mCi/2 = 3.1 mCi
b) About how many days will it take for the 25 mCi sample to decay to an activity
below 1 mCi?
25 mCi/2 = 12.5 mCi
3.13 mCi/2 = 1.56 mCi
12.5 mCi/2 = 6.25 mCi
6.25 mCi/2 = 3.13 mCi
1.56 mCi/2 = 0.78 mCi < 1 mCi
5 half-lifes x 14 days = 70 days
9. Positron emission tomography (PET) is a medical imaging technique that uses
positron emitters, such as oxygen-15.
a) What type of radiation is detected with PET?
Gamma radiation
b) Write the equation for the positron decay of oxygen-15.
15O

15N
+ e+
10. Without looking in your book (except for the periodic table in the front), fill out the
following table:
Name of
Element
Symbol
Atomic
Number
#
Electrons
in
1s orbital
#
Electrons
in
2s orbital
#
Electrons
in
2 p orbitals
#
Electrons
in
3 s orbitals
#
Electrons
in
3p
orbitals
Carbon
Silicon
Fluorine
Hydrogen
Sodium
Oxygen
Sulfur
Phosphorus
Beryllium
Boron
Magnesium
Argon
C
Si
F
H
Na
O
S
P
Be
B
Mg
Ar
6
14
9
1
11
8
16
15
4
5
12
18
2
2
2
1
2
2
2
2
2
2
2
2
2
2
2
0
2
2
2
2
2
2
2
2
2
6
5
0
6
4
6
6
0
1
6
6
0
2
0
0
1
0
2
2
0
0
2
2
0
2
0
0
0
0
4
3
0
0
0
6
11. Finish filling out the table below with chemical symbols, using the above
information. Note valence electrons are electrons in the outermost shell of the atom.
Shell containing
Valence electrons
1 (1s orbital)
2 (2s & 2p orbitals)
3 (3s & 3p orbitals)
1
2
# VALENCE ELECTRONS
3
4
5
6
H
Li
Na
He
Be
Mg
N/A
B
Al
N/A
C
Si
12. Do you see a pattern in the above table? Explain.
Yes, it is the first part of the periodic table.
13. Write the electron configuration for phosphorus.
1s22s22p63s23p3
or
[Ne]3s23p3
N/A
N
P
N/A
O
S
7
8
N/A
F
Cl
N/A
Ne
Ar