Exploring Atoms, Molecules and Ions
Name ______________________________
Group _______
Matter in our universe is made up of tiny, individual particles called atoms. Atoms are made up of even
smaller particles called proton, neutron, and electron.
Exploring atoms and sub-atomic particles
Open the PhET simulation Build an atom. Click on the “Atom” icon. Expand the box labeled “net charge”.
1. Pick up a proton and drop it inside the smaller blue circle. Which element have you made and what is its net
charge?
2. Pick up another proton and drop it inside the smaller blue circle. Which element have you made and what is
its net charge?
3. Pick up one more proton and drop it inside the smaller blue circle. Which element have you made and what
is its net charge?
4. Pick up one more proton and try to place it outside of the small blue circles. What happens?
5. Put all the protons back into the bucket. Repeat steps 1 - 4 with neutrons. Describe what happens.
6. Put all the neutrons back into the bucket. Repeat steps 1 - 4 with electrons and describe what happens.
7. Answer the following questions based on your observations from steps 1 - 6.
What is the charge of:
Each proton?
Each neutron?
Each electron?
Where in the atom are the protons located?
Where in the atom are the neutrons located?
Where in the atom are the electrons located?
Which sub-atomic particles, protons, neutrons or electrons, determine the type of element? Justify your
answer.

Check with your instructor before proceeding
Clear your atom and expand the box labeled “mass number”.
8. Add a proton to your atom. Record the mass number.
Mass number after 1 proton __________________
Mass number after 2 protons _________________
9. Keep the protons in the atom and add a neutron. Record the mass number
Mass number after 1 neutron __________________
Mass number after 2 neutrons__________________
10. Keep the protons and neutrons in the atom and add an electron. Record the mass number.
Mass number after 1 electron __________________
Mass number after 2 electrons _________________
11. Based on the observations above, what mass number would you assign to each proton, neutron and electron?
12. If you know the number of protons, neutrons and electrons in an atom, how would you calculate the mass
number of the atom?

Check with your instructor before proceeding
Ions
When atoms become charged, they form ions. Ions are building blocks of ionic compounds such as the table salt
that we sprinkle on French fries. An ion with a positive charge is called a cation; an ion with a negative charge is
called an anion.
13. Prediction: How can an atom become positively charged? How can it become negatively charged?
14. In the simulation, try to create the following atoms or ions. Draw a schematic diagram in the space below.
A neutral lithium atom
(with 4 neutrons)
A lithium ion with + 1 charge
(with 4 neutrons)
A lithium ion with – 1 charge
(with 4 neutrons)
Isotopes
Isotopes are atoms of the same element with different mass numbers.
15. Prediction: Based on the definition of isotopes and what you have learned from the simulation, what can you
predict about the number of protons and neutrons in different isotopes of the same element?
Different isotopes of the same element have ___________ (same or different) number of protons;
Different isotopes of the same element have ___________ (same or different) number of neutrons.
Open the PhET simulation Isotopes and atomic mass. Expand the box labeled “symbol”.
16. Build the following isotopes in the simulation.
Isotope
Symbol of isotope
# of protons
# of neutrons
Hydrogen-1
Hydrogen-2
Hydrogen-3
Lithium-7
Lithium-8
17. What can you tell about the atom represented by the following symbol?
Is there any redundant information in the above symbol?

Check with your instructor before proceeding
# of electrons
Building models of atoms, isotopes and ions with the atomic board
Each group will need one atomic model board and a set of colored beads.
18. Using your understanding of atoms, isotopes and ions, construct models of the following atoms or ions on the
atomic model board. Use orange beads as protons, clear beads as neutrons, and green beads as electrons.
After you’re done, draw a schematic diagram of each atom or ion below.
Hydrogen-1:
Hydrogen-2:
Hydrogen-3:
A neutral oxygen atom with a symbol of 8 O
7
A lithium 3 Li ion with + 1 charge.
Is it a cation or an anion?
16
A fluorine 9 F ion with −1 charge.
Is it a cation or an anion?

Check with your instructor before proceeding
18
Molecules
Some matter such as helium in carnival balloons consist of individual atoms. Other matter consists of building
blocks with more than one atom. Two atoms of the same kind can combine to form molecules such as O2 that we
breathe. Molecules that consist of only ONE type of atom are called an element. Other examples of elements
include N2 and H2. Atoms of different kinds can also combine to form molecules such as the water (H2O) we drink
and the sugar (C12H22O11) we enjoy in candies. These molecules consist of more than one type of atom, which make
them compounds. Other examples of compounds include carbon dioxide (CO2) and carbon monoxide (CO).
Open the PhET simulation Build a molecule.
19. A. Build the following molecules from atoms. Try out different ways atoms are connected together. After you
build a molecule, drag and drop it into the bin underneath the molecule name. Only atoms connected correctly
can be dropped into the bin.
B. After the correctly connected molecules are dropped into the bins, click on the “3D” button to see what
each molecule looks like. Check out both “space-filling” and “ball-and-stick” models. Draw the ball-and-stick
model of each molecule in the space below.
Hydrogen (H2)
Water (H2O)
Oxygen (O2)
Nitrogen (N2)
Carbon dioxide (CO2)
20. List some different features that you see from the ball-and-stick models of the five molecules above.
Building molecules with a molecular model set.
21. Obtain a molecular model set. Figure out what atoms different color of balls represent and what different
sticks (white, short grey, long grey) are for. Build the ball-and-stick models of the five molecules on the
previous page.
22. Below is the structure of ethylene, the monomer used to make both high-density polyethylene (HDPE) and
low-density polyethylene (LDPE). Use the molecular model set to build the ball-and-stick model of an ethylene
molecule. Show the lab instructor the model you build.