DIRECTIONS: Drag a proton into the atom model (x with two dashed circles around it). Click on "Net Charge" to see if what you have made has a charge or not. Next, click on "Mass Number" to find out the atom's atomic mass.

QUESTION: What happens when you drop the proton into the model?

• It forms the element hydrogen which has a positive charge and an atomic mass of 1.

• Nothing

• It forms the element hydrogen which has a negative charge and no mass.

• It forms the element hydrogen which has a neutral (no) charge and atomic mass of 1.

DIRECTIONS: Add a neutron to your model from the previous question.

QUESTION: What happens to the element when you add a neutron?

• Nothing changes.

• The charges do not change, but the atomic mass does.

• The charges and mass number change.

• The charges change, but the atomic mass does not.

DIRECTIONS: Add an electron to your atom of hydrogen.

QUESTION: What happens to the atom? Select all that apply.

• Its becomes a new element (not hydrogen anymore).

• It remains hydrogen.

• Its charge stays the same.

• Its charge increases to +2.

• Its charge decreases to 0.

DIRECTIONS: Select the best answers from the dropdowns to fill in the blanks and complete the statement.

QUESTION: Adding a proton​ (a)   the charge, meaning that protons have a​ (b)   charge. Adding a neutron​ has no effect on the charge, meaning that neutrons have a​ (c)   charge. Adding an electron​ (d)   the charge, meaning that electrons have a​ (e)   charge.

• increases
• positive
• decreases
• negative
• neutral

DIRECTIONS: Based on your observations from when you added protons, neutrons, and electrons to the model, complete the statement below.

QUESTION: ​ Both protons and neutrons​ (a)   the mass by​ (b)   . Adding an electron​ (c)   change the mass. This is because its mass is so small it is ignored. in terms of their individual mass, protons are​ (d)   to neutrons and both are​ (e)   electrons.

• increase
• 1
• does not
• equal
• greater than
• decrease
• does
• less than

DIRECTIONS: Add another proton to your model and check what happens.

QUESTION: Which of the following best describes what changes?

• Just the charge changes.

• Just the mass changes.

• The mass and the charge change, but nothing else.

• The mass, the charge, and the name of the atom change.

QUESTION: Based on your observations so far, which subatomic particle determines what element an atom is (its name)?

• Nucleus

• Electron

• Neutron

• Proton

DIRECTIONS: Reset the sim and check the box towards the bottom-right corner that says "Stable/Unstable." Add two protons and nothing else.

QUESTION: Is the atom you built stable or unstable?

• Stable

• Unstable

• Cannot tell

DIRECTIONS: Add one electron to your two-proton atom and check its stability. Next, add one neutron and again check its stability.

QUESTION: Which subatomic particle was able to stabilize your atom?

• electron

• neutron

• both

• neither

DIRECTIONS: Make sure that all of the boxes under "Show" are checked. Add or remove any number of neutrons to your atom.

QUESTION: Which property does NOT change?

• The element's name

• The mass number

• The atomic structure

• They all change