1. Atomic structure
Building atoms

2. ChemCatalyst
A Bohr model of a helium atom and a beryllium atom are given below.
Helium, He
Berylium, Be
(cont.)
Unit 1 • Investigation III

3. a. List three similarities and three differences between the drawings
b. How do you think a gold atom would be represented different from a copper atom?
Unit 1 • Investigation III

4. Compare Helium and Berylium

5. Differences between Gold and Copper?

6. The Big Question
What does the periodic table tells us about the structures of different atoms?
Unit 1 • Investigation III

7. BY the end of the section, you should be able to:
Use the periodic table to identify the number of:
protons, neutrons, electrons
in a neutral element’s atom.
2: Determine what the atomic number represents about the atom
3. Determine the atomic mass of any atom
Unit 1 • Investigation III

8. Opening questions in the lab
1. For each atom shown to be neutral, what must be true about the number of protons and electrons it has?
2. How can you identify the neutrons in the diagrams?
3. List the number of electrons, protons and neutrons for each atom shown

9. Bohr Models of atoms
Beryllium Atom
Fluorine Atom
Carbon Atom

10. Comparison
Compare the numbers in the periodic table to the pictures of the atoms
What connections do you see?

11. HOW DO YOU DETERMINE THE NUMBER OF PROTONS IN AN ATOM?

12. Atomic number Whole number
Equals the number of protons in a single element atom

13. Proton changes
If a proton is added or subtracted to atom, the atom becomes a new element!

14. Question set 1 How many protons do Ca, HS, Kr have?
What element has 48 protons
If I can add 1 proton to a gold atom, what have I created?

15. HOW DO YOU DETERMINE THE NUMBER OF ELECTRONS IN AN ATOM?

16. Determining electrons
If the atom is neutral, the number of electrons equals the number of protons
# protons = Atomic # = # electrons

17. Question set 2 How many electrons does a neutral atom of Cs Hg Br
Have?

18. HOW DO YOU DETERMINE THE ATOMIC MASS OF AN ATOM?
Atomic mass and mass number describe the same thing

19. Determining the Mass Number of an atom
Is the mass of an individual atom
Sum of protons and neutrons in nucleus
Each proton or neutron has a mass value of 1 atomic unit (1 amu)
Electrons’ mass are insignificant (why?)

20. Atomic weight Why is the Atomic weight usually a decimal?
Since mass value is arbitrarily assigned , could also be used to represent weight
The number on the periodic table represents the average mass (weight) of an individual atom of a specific element
Why is the Atomic weight usually a decimal?
Unit 1 • Investigation III

21. Answering questions with questions
Do stable atoms have parts of protons or neutrons?
Do all atoms of the same element have the same number of protons and neutrons?

22. Answers
The Atomic weight is the average weight(mass) of EVERY atom of that element
Not all atoms are the same
No partial subatomic particles

23. To determine the mass number of the most common version of an element
Round off the weight to the nearest whole number

24. Question set 3
If an atom had 23 protons and 24 neutrons, what would be its mass number?
What is the mass number of the most common version of Vanadium?
What is the atomic weight of Argon? Its most common mass number?

25. HOW DO YOU DETERMINE THE # OF NEUTRONS IN AN ATOM?

26. Determining neutrons
Subtract the number of protons (represented by the atomic number) from the atomic mass of the atom
Neutrons = Mass number – Atomic number

27. Question 4
What is the number of numbers in the most common version of the following atoms: Be Rn La

28. In your Comp Book
Draw a Lithium atom with 4 neutrons using the Bohr-orbital style
Check with your neighbors, any variations?

30. Class/Lab assignment
Each Person must complete their own chart. Students at table may work together.
Identify the names of the unknown elements
You may use a periodic table to help you complete the chart

31. “Building atoms” Chart
element
chemical symbol
atomic number
# of protons
# of electrons
# of neutrons
mass number
atomic weight
beryllium 5
fluorine 10 6 12
chlorine 18
35.45
lead
126
potassium 19 39
tin 70
tungsten
184
183.85 29 36
gold
118
Unit 1 • Investigation III

32. Questions on the chart?

33. Conclusions Looking at the periodic table:
What number indicates the amount of protons found in each element’s atom?
What number used to organize elements on the periodic table?
(each element has a unique value,
arranged sequentially)

34. What would you have to do to turn a copper atom into a gold atom?
Is there a better element to start with than copper? Why?

35. Check-In Use your periodic table to identify the following elements:
a) Element that has an Atomic number of 18
b) Neutral element that has three electrons
c) Element that has an Atomic mass of 16.0
d) The number of neutrons an atom of Iridium has is its atomic mass is 192 amu
Unit 1 • Investigation III

36. Making Sense
If you know the atomic number of an element, can you figure out how many neutrons an atom of that element has? Can you come up with a close guess? Explain.
Unit 1 • Investigation III

37. Wrap-Up
Each successive element has one more proton than the element preceding it.
The atomic number is equal to the number of protons.
The atomic mass equals the sum of the number of protons and neutrons in an atom
The atomic weight is the average mass of all atoms of an element. It is the decimal value found on the periodic table
(cont.)
Unit 1 • Investigation III

38. If you finish early…
Look at Te and I in the periodic table. What is unusual about their numbers in the table
Are there other examples in the periodic table?
Why does Iodine (I) not have an atomic weight higher the Te (tellurium)?

39. WHY ARE THE MASSES OF ALL CARBON ATOMS NOT THE SAME?

40. The answer
The number of neutrons can vary in atoms of a specific element