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24
ChemQuest 8
Name: ____________________________
Date: _______________
Hour: _____
Information: Structure of the Atom
Note the following symbols: (they are not to scale)
= proton (positive charge)
= electron (negative charge)
= neutron (no charge)
The following three diagrams are hydrogen atoms:
1
1
2
1
H
3
1
H
H
The following three diagrams are carbon atoms:
12
6
13
6
C
(6 protons, 6 neutrons)
Notice the type of notation used for atoms:
(6 protons, 7 neutrons)
A
Z
14
6
C
C
(6 protons, 8 neutrons)
X
X = chemical symbol of the element
Z = “atomic number”
A = “mass number”
12
6
1
1
C , 136 C, and 146 Care notations that represent isotopes of carbon.
3
H , 21 H and 1 H are notations that represent isotopes of hydrogen.
The part of the atom where the protons and neutrons are is called the nucleus.
Copyright 2002-2004 by Jason Neil. All rights reserved.
25
Critical Thinking Questions
1. How many protons are found in each of the following:
1
1
H ? in 21 H ? in 31 H ?
1
2. How many neutrons are found in each of the following:1 H ? in
3. How many electrons are found in each of the following:
1
1
2
1
H? in 31 H ?
H ? in 21 H ? in 31 H ?
4. What structural characteristics do all hydrogen atoms have in common?
5. What structural characteristics do all carbon atoms have in common?
6. What does the mass number tell you? Can you find the mass number of an element on the
periodic table?
7. What does the atomic number tell you? Can you find the atomic number of an element on the
periodic table?
8. Define the term isotope.
9. How does one isotope of carbon differ from another isotope of carbon?
Copyright 2002-2004 by Jason Neil. All rights reserved.
26
Information: Atoms, Ions, Masses of Subatomic Particles
The atomic mass unit (amu) is a special unit for measuring the mass of very small particles such as
atoms. The relationship between amu and grams is the following: 1.00 amu = 1.66 x 10-24g
Note the following diagrams comparing atoms and ions.
Atom
Ion
9 protons
10 neutrons
9 protons
10 neutrons
19
9
19
9
F
mass = 18.9980 amu
F -1
mass = 18.9985 amu
Atom
Ion
12 protons
12 neutrons
12 protons
12 neutrons
24
12
Mg
mass = 23.9978 amu
24
12
Mg + 2
mass = 23.9968 amu
Critical Thinking Questions
10. What is structurally different between an atom and an ion? Note: This is the ONLY structural
difference between an atom and an ion.
11. In atomic mass units (amu), what is the mass of an electron?
12. Is most of the mass of an atom located in the nucleus or outside the nucleus? How do you know?
Copyright 2002-2004 by Jason Neil. All rights reserved.
27
13. If protons and neutrons have the same mass, what is the approximate mass of a proton and
neutron in atomic mass units (amu)?
14. The mass of
and 13?
14
6
C is about 14 amu. Does this agree with what you determined in questions 11
15. The charge (in the upper right hand corner of the element symbol) is –1 for a fluorine ion. Why
isn’t it +1 or some other number?
16. What is the charge on every atom? Why is this the charge?
17. How do you determine the charge on an ion?
18. An oxygen ion has a –2 charge. (Use your periodic table if necessary)
a) How many protons does the oxygen ion have?
b) How many electrons does the oxygen ion have?
Copyright 2002-2004 by Jason Neil. All rights reserved.
28
ChemQuest 9
Name: ____________________________
Date: _______________
Hour: _____
Information: Weighted Averages
Examine the table of student test scores for five tests they have taken.
Test
1
2
3
4
5
Average Grade
Student A
95
74
82
92
81
Student B
76
88
90
81
72
Critical Thinking Questions
1. Calculate the average grade for students A and B and enter the average in the table above.
2. If you know a student’s average grade can you tell what the student’s individual test scores were?
Explain.
3. Suppose student C had an average of 83%. On each of his five tests he scored either 65% or
95%. Which score occurred more often? Explain.
4. What if the teacher decided that test five would count for 40% of the final grade and test four
would count for 30% of the final grade and each of the other tests would count for 10%.
Calculate the new average for each student. Note: this is called the weighted average.
Student A’s new average: _____________ Student B’s new average: _______________
Copyright 2002-2004 by Jason Neil. All rights reserved.
29
Information: Average Atomic Mass
On the periodic table you can find the average atomic mass for an element. This average is a
weighted average and it tells you the average mass of all the isotopes of an element. The periodic
table does not contain mass numbers for individual atoms, instead you can find the average mass of
atoms. The average atomic mass is calculated just how you calculated the weighted average in
question 4 above.
Critical Thinking Questions
5. Neon has three different isotopes. 90.51% of neon atoms have a mass of 19.992 amu. 0.27% of
neon atoms have a mass of 20.994 amu. 9.22% of neon atoms have a mass of 21.991 amu. What
is the average atomic mass of neon?
6. Chlorine-35 is one isotope of chlorine. (35 is the mass number.) Chlorine-37 is another isotope
of chlorine. How many protons and how many neutrons are in each isotope of chlorine?
7. Of all chlorine atoms, 75.771% are chlorine-35. Chlorine-35 atoms have a mass of 34.96885
amu. All other chlorine atoms are chlorine-37 and these have a mass of 36.96590. Calculate the
average atomic mass of chlorine.
8. Do your answers for questions 5 and 7 agree with the average atomic masses for neon and
chlorine on the periodic table?
Copyright 2002-2004 by Jason Neil. All rights reserved.
30
Skill Practice
9. Complete the following table.
Symbol
31
15
28
13
# of neutrons
# of protons
# of electrons
Atomic #
Mass #
38
38
80
P
Al +3
119
50
Sn
8
84
84
7
10
210
10. A certain element has two isotopes. One isotope , which has an abundance of 72.15% has a mass
of 84.9118 amu. The other has a mass of 86.9092 amu. Calculate the average atomic mass for
this element.
11. Given the following data, calculate the average atomic mass of magnesium.
Isotope
Magnesium-24
Magnesium-25
Magnesium-26
Mass of Isotope
23.985
24.986
25.983
Copyright 2002-2004 by Jason Neil. All rights reserved.
Abundance
78.70%
10.13%
11.17%