1. Atoms & the Atomic Theory
Atoms are tiny particles that make up all matter.

2. Discover the Elements
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3. Atoms
What are atoms?

4. Quick Write
Why do you think Aristotle developed the idea that matter was made of 4 elements and in 4 arrangements?

5. Democritus Greek Philosopher
Proposed the first idea of an atom 2000 years ago
Atomos meaning unable to divide
Some people believed him; most did not
Why? Would you believe him?

6. Democritus first suggested the existence of the atom but it took almost two millennia before the atom was placed on a solid foothold as a fundamental chemical object by John Dalton ( ). Although two centuries old, Dalton's atomic theory remains valid in modern chemical thought.

7. John Dalton

8. Questions to Ponder?
Why do you think Dalton’s idea of the atom was accepted?
Was Dalton smarter or did he have something that Democritus did not?

9. Dalton’s Atomic Theory
1) All matter is made of atoms. Atoms are indivisible and indestructible.
2) All atoms of a given element are identical in mass and properties
3) Compounds are formed by a combination of two or more different kinds of atoms.
4) A chemical reaction is a rearrangement of atoms.

10. Dalton’s Atomic Theory
Many unexplained chemical phenomena were quickly explained by Dalton with his theory. Dalton's theory quickly became the theoretical foundation in chemistry.

11. Crooke
Came up with the idea of a charged particle by using a cathode tube Watch the demonstration. what do you notice? how does the image change?

12. J.J. Thomson
British scientist
In 1897 while experimenting with a cathode tube, Thomson observed one end to be positively charged and the other end negatively charged.
This experiment suggested that the negatively charged particles came from inside atoms
Plum pudding model or blueberry muffin model
Discovered the electron

13. Ernest Rutherford British scientist 1899 revised Thomson’s model
How did the Gold-foil experiment resulted in the discovery of nucleus?
What did Rutherford’s model look like compared to Dalton’s and Thomson’s

14. Neils Bohr Danish Physicist
proposed that electrons orbited in levels like planets orbit the sun
Electrons could be excited by gaining energy from packets called photons and move to a higher energy level.
Electrons could lose energy and move to a lower ground state

15. Main Points of the Bohr Model
Electrons orbit the nucleus in orbits that have a set size and energy.
The energy of the orbit is related to its size. The lowest energy is found in the smallest orbit.
Radiation is absorbed or emitted when an electron moves from one orbit to another.
According to Bohr, when an electron loses energy, predict what happens to that electron?
What state is that electron in when it gains energy?

16. Bohr’s Model

17. Planetary Model of an Element

18. What is in an Atom? Identify the parts of the atom Compare:
Size of the subatomic particles
Charge of the subatomic particles
Location of the subatomic particles
Illustrate a modern model of the atom.

19. Structure of the Atom Subatomic particles
Protons : positively charged (p+); located in nucleus
Neutrons: neutral charge (n); located in nucleus
Electrons: negatively charged (e-); located in electron cloud

20. Questions to Ponder? How is an atom identified?
By the number of protons?
By the number of neutrons?
By the number of electrons?
How can the number of protons, neutrons and electrons be calculated?

21. Atom Structure Each element has a unique number of protons.
In a neutral atom, the number of electrons equal the number of protons.
The number of protons = atomic number
Mass number = #protons + #neutrons
Why do you think that the mass number does not include electrons?

22. Build an Atom
Go to
Which particles (the colored balls) go in the middle?
Which particles go on the blue rings?
How can you make the atom unstable?
How do you fix it to make it stable again?
How do you make the atom say it is neutral?

23. Build an Atom (continued)
Click on the plus sign beside Net Charge
Which particles change the net charge?
When is the net charge positive?
When is it negative?
When is it zero (neutral)?
Click the plus sign by mass number.
Which particles change the mass number?
What is the mass number equal to? (Hint: count the particles!)

24. Calculations
Calculate the number of protons by looking at the atomic number.
Number of Neutrons = mass number – atomic number
Calculating Number of Electrons:
If the charge is neutral, then electrons = protons
If the atom carries a charge, then set up a math equation and solve.
Example: 12 p+
? e-
= +2

25. Isotopes
An atom that has the same number of protons but a different number of neutrons
Isotopes vary in mass. Why?
Some isotopes are more common than others.
Compare the isotopes of hydrogen.
How do their masses differ?
Do you think their chemical properties change as a result of having different number of neutrons? Please explain!

26. Average Atomic Mass Average of all of the common isotopes.
Where can this number be found?
Look at an element’s square on the periodic table.
It is the long number at the bottom of the square. The one that is under the letter(s).

27. Isotope Notation

28. Isotope Notation Practice

29. Calculating Neutrons
Help! I need to know how many neutrons there are. If chlorine-35 has 17 protons, how many neutrons are there?
Calculate the number of neutrons for:
Boron-11
Boron-10
Carbon-12
Carbon-14

30. Modern Atomic Theory
Using your textbook and workbook, create your own notes of the modern atomic theory.
Share and compare with 2 other students near you.
You have 5-7 minutes.

31. Student activity option
Group 1:
Key Term: atomic mass:
define in your own words;
give examples complete with pictures;
explain how you can use the atomic number to determine the number of protons and electrons in a neutral atom;
explain what happens to the atomic number when the number of protons changes and how this relates to knowing which element it is.
see your textbook; your glossary and reading workbook
come up with 2 questions to ask your peers that relates to atomic mass
Group 3
Key Term: Isotopes
2. give examples complete with pictures;
3. explain how isotopes differ and how to determine the number of protons and neutrons
4. explain what happens to the atomic number when the number of protons changes and how this relates to knowing which element it is.
5. see textbook; your glossary and reading workbook
6. come up with 2 questions to ask your peers that relates to isotopes
Group 2
Key Term: mass number:
give examples;
Explain how the mass number is related to the atomic number
come up with 2 questions that relates to mass number to ask the class
Group 4
Scanning Tunneling Microscope pg. 111
What is it?
What is it used for?
How is the distance between the probe tip and the sample kept constant?

32. Atom Lab Procedures Analysis
Take the doughnut or cake and cut/tear in half.
Examine the parts.
Illustrate and label the parts of the doughnut or cake.
Add corresponding atomic particle and region labels to the drawing of the doughnut or cake.
Analysis
How is the doughnut or cake represent the parts of the atom?
Center (the jell portion)
Cake
Chocolate Frosting
What everyday item would you recommend as a model of an atom that would demonstrate the subatomic parts?

33. Moles to Grams
Avododro’s Number allows us to count a large amount of small particles.
6.022 x 10²³

34. Bell Work