CHE 105 – Week 3

Formative Assessment.

Instructions:  

• Each student will work on this assignment alone.  
• Assignments with identical answers will earn grades of zero.  
• If you have questions, you are to ask me, your instructor, not your peers.
• The assessment will be printed out, completed, scanned, or photographed and uploaded to the upload area.  Only assignments uploaded to the class will be graded.
• You must show ALL work.  Submissions with answers only will not be evaluated.

Formats:  

The following formats will be evaluated:

• Microsoft Word

Note: if you cannot scan your work before submitting, you are welcomed and encouraged to do the following:

• Take an image of each page of your work with your phone.  
• Copy/paste those images to a Word document.
• Make sure the image size is the same as the page. Submit one image per page.
• Save the file as a Word document. 

Submitted files in the following formats will NOT be evaluated:

• Pages
• Lone Jpeg images
• Any other file formats

Introduction: Structure of the atom

Part 1: Atomic structure

The following exercise involves an understanding of the structure and component parts of an atom.  The main things to consider before completing this assignment are:

• The atom is composed of two primary regions:
  • An atomic nucleus at the center which is constructed with protons and neutrons of different numbers.  The number of protons determines which atom we are discussing.
  • Electrons, which are found in zones of probability called ‘orbitals’ surrounding the nucleus.
• Both protons and neutrons have roughly the same mass, 1 AMU, which is 1.67 x 10^-24 grams.
• Each electron has a negative charge.
• Each proton has a positive charge
• Each neutron has no charge.
• A neutral atom has no net charge.
• A charged atom is the result of a loss or gain of some unit of charge, either an electron or a proton.  Usually – it’s the electron which leaves or joins.

Part 2: Evaluate:

Review the following diagram and answer the following questions:

• How many protons are found in
  • ¹²C? _____
  • ¹³C?  _____
  • ¹³C^–? _____
• How many neutrons are found in
  • ¹²C? ____
  • ¹³C?  _____
  • ¹³C^–? _____
• How many electrons are found in
  • ¹²C? _____
  • ¹³C?  _____
  • ¹³C^–? _____
• What feature distinguishes a neutral atom from an ion?

• How would you calculate the charge in the ion?

• Based on the model on the picture,
  • what do all carbon atoms (and ions) have in common?

• what do all hydrogen atoms (and ions) have in common?

• how many protons, neutrons, and electrons are there in one atom of 1H⁺?

Part 3: Collect the data and interpret using PhET similator

1. Neutral Atom: instructions:
2. Go to the web site: https://phet.colorado.edu/sims/html/build-an-atom/latest/build-an-atom_en.html
3. Start with the Build Atom icon. Make sure that all of the <+> boxes on the right of the screen are open. You should see the following picture:

• Add protons and neutrons to the nucleus by dragging them from the bowl to the orbit. Watch what happens to the Periodic Table, Atomic Symbol, the Mass Number and the Net Charge.
• Add electrons and watch the Net Charge.
• Try a variety of different combinations of protons, neutrons, and electrons.
• Complete the table below for the first 10 elements.
  • You want to have a stable nucleus and a ZERO net charge.
  • Start with 1 proton and 1 electron. This is hydrogen. Record the numbers in the table.
  • Add a second proton and the add neutrons until the nucleus is stable. Add electrons so that you have a zero net charge. Record the values.
  • Continue through to Atomic Number 10.

DATA
Symbol	Name	Atomic Number	Mass Number	Number of Protons	Number of Neutrons	Number of Electrons
H
He
Li
Be
B
C
N
O
F
Ne

Questions

1. Which particles contribute to the mass number and which do not? Why?

• Which particle contributes to the atomic number and why?

• Which particles contribute to the net charge and how does each change the net charge?

B.    Isotopes

For all elements, the number of neutrons can make the nucleus stable or unstable. The Nuclear Strong Interaction (also called the nuclear strong force or nuclear force) is what holds the nucleus together. Neutrons help hold the protons the right distance apart from each other to maintain nuclear stability.

Different isotopes of the same element are written in words and symbols to show the mass number.  (Recall that mass number is the number of protons and neutrons). For example, the two isotopes of Carbon that discussed were carbon-12 and carbon-14.  The symbolic notation for these two isotopes would be:

        for carbon 12 with an atomic number of 6 and a mass number of 12.

              for carbon 14 with an atomic number of 6 and a mass number of 14

Activity:

1. Go back to the simulation at https://phet.colorado.edu/sims/html/build-an-atom/latest/build-an-atom_en.html. Click on Symbol:

Your next screen should look like the following picture:

• Start by creating the isotope oxygen-16. This will have 8 protons, 8 neutrons, and 8 electrons. 
  • What is the symbolic notation for this isotope?  ____________
  • Is this isotope stable or unstable?________________________