2. Level A
Atom Building
What is inside an atom?

3. Investigation Topics
Identify and describe particles which comprise atoms.
Build Bohr models of stable, neutral atoms.
Relate the structure of an atom and it’s position on the periodic table.
Materials:
Atom Building Game

4. Subatomic Particles What three basic particles make up all atoms?
Most adults will know the terms proton, neutron and electron.

5. Can you guess which marble represents which particle?
Everyone will guess that the small yellow marbles are electrons, which is correct. The electron is represented with a small marble because it contributes almost no mass to the atom. However, no one will know for sure which particle goes with red and blue marbles, since they are the same size and protons and neutrons contribute equally to the mass of the atom.
A Modeling an atom
Red marbles = protons
Blue marbles = neutrons
Yellow marbles = electrons
In the atom game, colored marbles represent the three kinds of particles.

6. Part 1 The Board Which particles are shown in the nucleus of the atom?
Where are the electrons located?
Take a moment to look at the diagram in the center of the page.
You can see that the atom represented in the diagram has three protons, three neutrons, and three electrons.
The protons and neutrons are in the nucleus.
The electrons are located in the energy levels. There are two electrons in the first energy level and one electron in the second energy level.
Build the atom shown in the diagram using the correct marbles. Then fill in the blanks in the empty periodic table box for the atom you constructed.

7. Build the atom shown in the picture.
Practice
Build the atom shown in the picture.
The model of the atom used in this activity is based on both the Bohr atom and the more modern quantum description of the atom.
The activities are designed to teach the basic ideas behind the structure of the atom.
These ideas include:
• Protons and neutrons are in the nucleus while electrons are outside the nucleus.
• The atomic number is the number of protons in the nucleus and determines which element an atom is.
• The mass number is the total number of particles in the nucleus and determines the isotope.
• Isotopes may be stable or unstable. Unstable isotopes are radioactive.
• Radioactivity occurs because the nucleus changes.
• The electrons in atoms are arranged in well-defined energy
levels.

8. Li Lithium What is the symbol for Lithium? 6,7 3
What is the atomic number?
How many lithium atoms are stable?
How many neutrons can lithium have?
Answer the questions for Part 2...
6,7 Li 3

9. Part 2 Thinking about the atom
a. What is the number below the element symbol called and what does this number tell you about the atom?
The number below the element symbol is called the atomic number, which indicates the number of protons in the nucleus.

10. Part 2 Thinking about the atom
b. What is the number above the element symbol called and what does this number tell you about the atom?
The number above the element symbol is the mass number, which indicates the total number of protons and neutrons in the nucleus. Some elements can have more than one mass number.

11. Part 2 Thinking about the atom
c. Why do some elements have more than one number above the symbol? What are the variations in this number called?
Some elements have more than one number above the symbol because there is more than one possible composition of the nucleus.
These different combinations are called isotopes. All isotopes of a particular element have the same number of protons but different numbers of neutrons.

12. Part 3 Making Atoms
Build the 6 atoms shown on the chart and fill in the missing information.

13. Part 3 Making Atoms

14. Part 4 Stop and think
a. Two of the atoms you made were the same element. What was different about them?
In steps 3b and 3c, carbon was made. One form of carbon had six neutrons while the other form had eight. As a result of the different numbers of neutrons, their mass numbers were also different. These two atoms are isotopes of carbon.

15. Part 4 Stop and think
b. One of the atoms had just enough electrons to completely fill the first two rows. Which atom was this? Where on the periodic table is it found?
This atom was neon. It is the last element in the second period (or row) of the periodic table.

16. Oxygen has an atomic number equal to eight.
Part 4 Stop and think
c. Which atom had an atomic number of 8?
Oxygen has an atomic number equal to eight.
d. Which atom had a mass number of 14?
Carbon-14 has a mass number equal to 14.

17. Part 4 Stop and think
e. One atom is found in a lightweight, silvery metal used in airplanes. Which atom was it?
The lightweight, silvery metal used in airplanes is aluminum.
f. One atom is found in an element that makes up about 21% of the air you breathe. You could not live without this element.
The atom is oxygen.