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# Building an Atom Mark as Favorite (26 Favorites)

SIMULATION in Model of the Atom, Atomic Theory, Subatomic Particles, Unit Plans. Last updated September 19, 2019.

### Summary

In this simulation, students manipulate the number of protons, neutrons, and electrons in an element and determine how these effect the mass number, atomic number, and other properties of an atom.

### Grade Level

Middle or high school

### Objectives

By the end of this lesson, students should be able to

• use the number of protons, neutrons, and electrons in an element to predict an atom’s identity.
• calculate atomic mass.
• calculate atomic number.
• understand ions.

### Chemistry Topics

This lesson supports students’ understanding of

• Atomic structure
• Mass number
• Atomic number
• Atomic charge
• Subatomic particles

### Time

Teacher Preparation: 10 minutes

Lesson: 2 class periods

### Materials

• Computer with internet connection

### Safety

No special safety precautions are necessary for this lab activity

### Teacher Notes

• It may be helpful to walk around the room to ensure students are staying on task.
• There are two handouts. One is an activity built around the simulation; the other allows students to summarize their findings in their own words. It’s essentially an extended conclusion.

### For the Student

###### Lesson

Purpose
Understand the roles of properties of protons, neutrons, and electrons in an atom.

Procedure

Visit the PhET simulation. Click the “play” button on the image to open the simulation. Choose the Atom version.

1. Add one proton to the nucleus of the atom (the X). What element did you just create? Notice that it’s also highlighted on the periodic table to the right.

2. Add another proton. What element do you now have?

3. Keep adding protons. Describe any patterns you notice.

Click on the reset button in the bottom right corner.

4. Add one proton and one neutron to the nucleus (X). Which element did you create?

5. Add another neutron. Which element did you create?

6. What changes when you add a second neutron?

7. Keep adding protons and neutrons to the nucleus. Describe any patterns you notice.

8. From the “Show” menu on the right, add a check mark by clicking the box next to the stable/unstable label. Using at least four protons, add neutrons and electrons to make a stable atom. What element did you create? How many protons, neutrons, and electrons does the atom have? Describe why you think it’s stable.

Element ___________ (____ p ____ n ____ e)

9. Now make an atom that is unstable. What element did you create? How many protons, neutrons, and electrons does it have? Describe why you think it’s unstable.

Element ____________ (____ p ____ n ____ e)

10. Describe what you think is meant by the term stable.

Click on the reset button.

11. Add one proton to the nucleus. Add one electron. Describe what happens when you add it (remove it and add it again if you missed it).

12. Add another electron. Describe what changes.

13. Add more electrons. What do you notice about where they are placed on the atom compared to the first two?

14. Add various amounts of protons, neutrons, and electrons. Describe any patterns you notice. How can you predict whether an ion is positive (+) or negative (-)?

15. What do you think is meant by the term neutral?

Click on the reset button. Expand the ‘Net Charge’ and ‘Mass Number’ menus by clicking the green + on the right side of the boxes. Change the numbers of protons, neutrons, and electrons and observe the effects of these changes on the net charge and mass number of the element. Answer the following questions after you’ve investigated what happens.

16. What variables are you manipulating in this exercise? Identify a symbol to represent each variable.

17. Using the symbols you just defined, write a math equation that explains how to calculate the mass number.

18. Using the symbols you defined, write a math equation that explains how to calculate the net charge.

At the bottom of the webpage, open the Symbol portion of the simulation by clicking on the Symbol icon. You will use the simulation to figure out what each part of the symbol represents in an atom.

19. Place an amount of protons, neutrons, and electrons in the atom so that you have a neutral, stable atom with at least five protons. What element did you create? How many protons, neutrons, and electrons does the atom have?

Element ___________ (____ p ____ n ____ e)

20. Explain what the letter(s) in the middle of the card represent.

21. Explain what the bottom left number represents.

22. Explain what the top left number represents.

23. Explain with the top right number represents.

24. Create a different ion. What number changes? Why?

25. Create an unstable atom. What number changes? Why?

If you finish early, try the games. At the bottom of the webpage, click on the Game icon. You can choose from four different games.