What is an Atom?
Name ________________________
1. Go to the web address www.phet.colorado.edu
then type Build an Atom in the search box. Click the link for
Build an Atom then click run now.
2. Click the green plus sign next to Symbol, Mass Number, and Net Charge so that all boxes are maximized.
3. Drag one proton in the center of the diagram where you see the X. Drag one electron toward the center.
4. Draw your diagram in the first box provided below. Use the following legend for drawing protons, electrons and neutrons for the entire activity.
Legend:
A dark circle for an electron (-)
An open circle for a proton (+)
A lightly shaded circle for a neutron (no charge)
5. In the upper right corner of the box, write the symbol found in the symbol box.
6. Below the diagram, write the mass number found in the mass number box.
7. Drag one neutron towards the center.
8. Draw your diagram in the second box including symbol and mass number.
9. Drag your neutron back to the container. Drag one more electron towards the center.
10. Draw your diagram in the third box including symbol and mass number.
Hydrogen Hydrogen Hydrogen
H H H
Mass number ____
Atomic mass 1.0078 amu
Mass number ____
Atomic mass 2.0140 amu
Mass number ____
Atomic mass 1.0083 amu
11. For the fourth diagram, drag a total of 6 protons, 6 neutrons, and 6 electrons towards the center. Draw and label everything as you have in the previous boxes.
12. For the fifth diagram, add one more neutron for a total of 6 protons, 7 neutrons, and 6 electrons.
13. For the sixth diagram, add one more electron for a total of 6 protons, 7 neutrons, and 7 electrons.
Carbon Carbon Carbon
C C C
Mass number ____
Atomic mass exactly 12 amu
Mass number ____
Atomic mass 13.0034 amu
Mass number ____
Atomic mass 13.0039 amu

14. For the next diagram, add a total of 8 protons, 8 neutrons, and 10 electrons. Fill in all the missing information in the diagram below.
Element name ___________
Mass number ____
Atomic mass 15.9960 amu
15. For the next diagram, add a total of 3 protons, 4 neutrons, and 2 electrons. Fill in all the missing information in the diagram below.
Element name ___________
Mass number ____
Atomic mass 6.941 amu
1 H and 2 H are isotopes of hydrogen. 12 C and 13 C are isotopes of carbon.
Inquiry Questions
1.
Play with the simulation to determine: a) Which particles affect the stability of the atom? _____________________ b) Which particles do not affect the stability of the atom? _______________
2.
Play with the simulation and create a definition (using a complete sentence) for each of these items based on the application. a) Element Symbol b) Charge c) Atomic Number d) Mass Number e) Isotope f) Ione

Critical Thinking Questions
1. How many protons are found in
12
C?
13
C?
13
C
-
?
2. How many neutrons are found in 12 C? 13 C? 13 C ?
3. How many electrons are found in
12
C?
13
C?
13
C
-
?
4. Based on your answers to questions 1-3, what do all carbon atoms (and ions) have in common?
5. Based on your diagrams, what do all hydrogen atoms (and ions) have in common?
6. Based on your answers to questions 4 and 5, what is the significance of the atomic number, Z, above each atomic symbol in the periodic table?
7. Based on your answer to question 6, what do all nickel (Ni) atoms have in common?
8. In terms of the numbers of protons, neutrons, and electrons: a) Why does the notation C
-
have a negative sign in the upper right hand corner? b) What feature distinguishes a neutral atom from an ion? c) Provide an expression for calculating the charge on an ion.
9. Determine the number of protons, neutrons, and electrons in one
1
H
+
ion. Explain how you found your answer.
10. What structural feature is different in isotopes of a particular element?
11. How is the mass number, A, (left-hand superscript next to the atomic symbol as shown in your diagrams) determined (from the structure of the atom)?
12. Show that the mass number and charge given for
16
O
2-
and
7
Li
+
are correct.

13. Based on your diagrams, where is most of the mass of an atom, within the nucleus or outside of the nucleus? Explain your reasoning using grammatically correct English sentences.
14. Using grammatically correct English sentences, describe what the isotopes of an element have in common and how are they different.
15. Draw a neutral atom of fluorine, then draw it as an isotope and then as an ion.
Symbol
12
C
6
+
1
Name
Carbon-12
18
F
9
11
5
B
Atom 1
12
C
6
Carbon-12
Argon-40
11
B
5
An atom with 13 protons and 13 neutrons
Atom 2
13
C
6
12
6
C
Argon-41
Boron-10
An atom with 14 protons and 13 neutrons
Relationship between atom 1 and atom 2
Isotopes
Same Atom, Not Isotopes of Each Other
Different Element
Isotopes
Same Atom, Not Isotopes of Each Other
Different Element
Isotopes
Same Atom, Not Isotopes of Each Other
Different Element
Isotopes
Same Atom, Not Isotopes of Each Other
Different Element
Isotopes
Same Atom, Not Isotopes of Each Other
Different Element

Using the periodic table, answer the following questions: a) What is the atomic number of chlorine (Cl)? _____ b) What is the atomic number of tungsten (W)? _____ c) How many protons are there in any Cl atom?_____ d) How many protons are there in any Te atom? _____ e) Can you tell from the periodic table exactly how many neutrons are in an atom?
Name hydrogen-2 sodium-22 carbon-12 carbon-13 carbon-14 carbon-12 carbon-12 argon-40
Symbol
4 He
2 H
3 H
22 Na +
46 Ti -2
107 Ag
19 F -1
70 Ga
70 Ga +3
8
18
Atomic number
1
12
12
4
7
Mass
Number
2
24
25
9
8
Number of neutrons
1
8
10
18
6
6
7
5
Number of
Electrons
1
10
12
13
6
2
8
Charge
0

1. Complete the following table.
ISOTOPE ATOMIC NUMBER Z MASS NUMBER A NUMBER OF ELECTRONS
31
P 15
18
O 8
58
Ni
2+
19 39
58
18
2. Define mass number.
3. Define atomic number.
4. Indicate whether the following statement is true or false and explain your reasoning.
An
18
O atom contains the same number of protons, neutrons, and electrons.
5. How many electrons, protons, and neutrons are found in each of the following?
24
Mg
23
Na
+ 35
Cl
35
Cl
56
Fe
3+ 15
N
6. Complete the following table.
16
O
227
Al
3+
ISOTOPE ATOMIC NUMBER Z MASS NUMBER A NUMBER OF ELECTRONS
27 59 25
14
N
3
3
7
6
3
3
58
Zn
2+
19
F
-