Element Builder
Some of the greatest breakthroughs in understanding the structure of the atom were provided by J.
J. Thompson during his time at the renowned Cavendish Laboratory in Cambridge, England.
Thompson had a reputation for being rather clumsy with his hands, and he always needed to have
assistants to set up equipment for him. Nevertheless, he was a brilliant experimental physicist. Work
conducted under his watchful eye led to the first discovery of a subatomic particle, the electron.
In this activity, you will create and alter various elements to observe the structural changes.
1) Go to the following website: www.explorelearning.com
2) Login using the following name and password:
Username:
Password:
4) Scroll to and Launch the Element Builder Gizmo
bannon
science
Atomic Number and the Identity of an Element
In this activity, you will examine the components of an atom's structure. As you work through the
different parts of the interactive lab, the questions are to be discussed by the group members.
When you finish working through the activity you will answer the set of questions on the
Knowledge Page.
1. In this Gizmo, subatomic particles (protons, neutrons and electrons) can be added to an
atom or removed from it by clicking the arrows next to each supply of particles. Remove any
protons, neutrons or electrons that are currently in the atom by clicking the left arrows.
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Using the right arrows, set it up so it has 2 protons, 2 neutrons, and 2 electrons in the atom.
1. Where in the atom are the protons and the neutrons located?
2. Where are the electrons located?
3.Which type of particle appears to be the smallest?

Check Show element name. 4. What is this particular element?

Experiment with adding and removing protons to and from the atom.
5. Does changing the number of protons change the identity of the element you have built?
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When you are done experimenting, make sure there are exactly two protons in the atom
again.
Perform a similar experiment, adding and removing neutrons, and then adding and
removing electrons.
6. Do these changes affect the identity of the element?
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

Build an atom again with exactly 2 protons, 2 neutrons, and 2 electrons.
Check Show element symbol. Now, check element notation.
The symbol for helium, He, is shown. The number to the upper left of the symbol indicates
the atomic mass of the atom (in this case it has a mass of 4). Again, experiment with
adding and removing protons, neutrons, and electrons.
7. Which particles affect the atomic mass?
8. Which particle does not?

You should have seen that protons and neutrons both affect the atomic mass of the atom,
and electrons do not. Both protons and neutrons have a mass that is almost exactly equal to
one atomic mass unit, or amu (one twelfth of the mass of a single carbon-12 atom). The
mass of an electron is less than one thousandth of an atomic mass unit. Adding and
removing electrons does change the mass of an atom, but only by a very small,
insignificant amount. Looking at the atom in the Gizmo,
9. where in the atom is most of the mass located?
.
 With Show element symbol still selected, create an atom again with exactly 2 protons, 2
neutrons and 3 electrons.
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Notice the 1− notation to the right of the element symbol. Protons and electrons each carry a
charge. Protons carry a positive charge and electrons carry an equal negative charge. The 1−
indicates the net charge of the atom. Atoms that have a net charge are said to be ionized, and
are called ions.

Remove one electron from the atom so that it once again has 2 protons and 2 electrons.
10. What is the net charge on the atom now? Explain.

Remove one more electron from the atom.
11. What is the net charge now? Explain why the charge is changing the way it does.
Name
Element Builder
Knowledge Page
Date
Period
Checking for understanding:
1. Where are the following particles located in an atom (are they in the nucleus or
not)?
a. Proton
b. Neutron
c. Electron
2. What happens when you added neutrons to an atom (what does it change)?
3. What happens when you added protons to the atom (what does it change) ?
4. Explain why atoms have a zero or neutral charge?
5. What particles add to the mass of an atom? Which one does not?
6. Based on your answer to number 5, where is the majority of an atom’s mass
located?
7. Which particle determines the identity of an element? Explain.
8. What happens to an element if it gains electrons and if it loses electrons? Give
an example.
9. What is the atom called if it loses or gains electrons?