1. Chapter 11 Material on Midterm
Introduction to Atoms
Chapter 11
Material on Midterm

2. Where is it?
How do we get information about items that we cannot see?

3. Section 1: Development of the Atomic Theory
Objectives
Describe some of the experiments that led to the current atomic theory
Compare the different models of the atom
Explain how the atomic theory has changed as scientists have discovered new information about the atom

4. History of the Atomic Theory

5. Section 1: Development of the Atomic Theory
The Beginning of Atomic Theory
Democritus
The particle that was so small it could not be cut again
The atoms Is the smallest particle into which an element can be divided and still be the same substance
Means not able to be divided

6. Section 1: Development of the Atomic Theory
The Beginning of Atomic Theory
Democritus
Challenged by Aristotle
Most believed him (even though he was wrong!)

7. Section 1: Development of the Atomic Theory
Dalton’s Atomic Theory Based on Experiments
Figured out that compounds are made of elements that are made of single atoms

8. Section 1: Development of the Atomic Theory
Dalton’s Atomic Theory Based on Experiments
Had three parts
All substances are made of atoms. Atoms are small particles that cannot be created, divided, or destroyed
Atoms of the same element are exactly alike, and atoms of different elements are different
Atoms join with other atoms to make new substances

9. Section 1: Development of the Atomic Theory

10. Section 1: Development of the Atomic Theory
Thomson’s Discovery of Electrons
Thomson used a device called a cathode ray tube
Determined that there are negative particles inside of an atom

11. Section 1: Development of the Atomic Theory

12. Cathode Ray Tube Experiment

13. Section 1: Development of the Atomic Theory
Electrons are subatomic particles that have a negative charge
Thomson created the Plum pudding model to show where the electrons go

14. Section 1: Development of the Atomic Theory
Rutherford’s Atomic “Shooting Gallery”
Rutherford wanted to test Thomson’s idea
Had a sheet of gold foil (SUPER THIN)
Had a detector on the outside
Shot a beam of positive particles at it
What he expected: all of the particles would just go right through

15. Section 1: Development of the Atomic Theory

16. Section 1: Development of the Atomic Theory
Rutherford’s Atomic “Shooting Gallery”
What really happened
Most went straight through (like he thought)
Some got bent at an angle
A few bounced right back!
“It was quite the most incredible event that has ever happened to me in my life. It was almost as if you fired a fifteen-inch shell into a piece of tissue paper and it came right back to you”

17. Section 1: Development of the Atomic Theory
Where are the Electrons?
Plum-pudding model was wrong!
Rutherford realized that atoms were mostly empty space
At the center is the nucleus
The nucleus is an atom’s central region, which is made up of protons and neutrons
Electrons move around it

18. Section 1: Development of the Atomic Theory
Bohr’s Electron Levels
Bohr figured out electrons move around in paths
Like rungs on a ladder

19. Section 1: Development of the Atomic Theory
Modern Atomic Theory
…it’s complicated
Schrodinger & Heisenberg and others helped
Electrons do not move in paths that are very clear
We cannot predict where electrons are exactly
We’re likely to find them in electron clouds, which are regions around the nucleus where electrons are likely to be found

20. Section 1: Development of the Atomic Theory
Section Summary
Please answer the objectives on your objective summary sheet
Describe some of the experiments that led to the current atomic theory
Compare the different models of the atom
Explain how the atomic theory has changed as scientists have discovered new information about the atom

21. History of the Atomic Theory

22. Section 2: The Atom Objectives Describe the size of an atom
Name and state information about the parts of an atom
Describe the relationship between number of protons and neutrons and atomic number
State how isotopes differ
Describe and calculate atomic masses
Describe the forces within an atom

23. 20 thousand billion billion atoms
Section 2: The Atom
How small is an atom?
Contains 2 x 1022
20,000,000,000,000,000,000,000
20 thousand billion billion atoms

24. Section 2: The Atom 1 aluminum atom has a diameter of 0.00000003 cm
How many atoms thick was our foil from chapter 1?

25. Section 2: The Atom What is an Atom made of? 3 major parts
The proton is the subatomic particle that has a positive charge and that is found in the nucleus of an atom
The neutron is the subatomic particle that has no charge and that is found in the nucleus of an atom
The electron is the subatomic particle that has a negative charge and that is found in the electron cloud surrounding the atom

26. Section 2: The Atom

27. Section 2: The Atom Scientists came up with a special term for them
How big are these pieces
VERY SMALL!
Scientists came up with a special term for them
The atomic mass unit is a unit of mass the describes the mass of an atom or molecule
Proton: ~1 amu
Neutron: ~1amu
Electron: ~1/8000 amu

28. Section 2: The Atom An atom is normally neutral
Same number of protons and electrons
If an atom changes this ratio, it becomes an ion

29. Section 2: The Atom How do Atoms of Different Elements Differ?
The atomic number is the number of protons in the nucleus of an atom; the atomic number is the same for all atoms of an element
An isotope is an atom that has the same number of protons/atomic number as other atoms of the same element but has a different number of neutrons (and this a different atomic mass)
The mass number is the sum of the protons and neutrons in an atom

30. Section 2: The Atom Proton Nucleus Positive Atomic identity Neutron
Subatomic particle
Location
Charge
Key feature
Proton
Nucleus
Positive
Atomic identity
Neutron
Neutral
Isotopes
Electron
Electron cloud
Negative

32. Section 2: The Atom Let’s do some practice!
An atom has a mass number of 7. It’s atomic number is 3. What is…
The number of protons?
The number of neutrons?
The number of electrons?
The name of the element?

34. Section 2: The Atom Let’s do some practice!
An atom has a mass number of 32. It’s atomic number is 16. What is…
The number of protons?
The number of neutrons?
The number of electrons?
The name of the element?

35. Section 2: The Atom Let’s do some practice!
An atom has a mass number of 1. It’s atomic number is 1. What is…
The number of protons?
The number of neutrons?
The number of electrons?
The name of the element?

36. Section 2: The Atom Naming isotopes
Remember, they are the SAME ELEMENT but differ in neutron number
Boron-10
Boron-11
5 protons
5 neutrons
5 electrons
Atomic number:
Mass number:
5 protons
6 neutrons
5 electrons
Atomic number:
Mass number:

37. Section 2: The Atom Calculating the mass of an element
The atomic mass is not really a whole number
The atomic mass is the mass of an atom expressed in atomic mass units
Hydrogen has an atomic mass of
Where does this number come from?

38. Section 2: The Atom Calculating the Mass of an Element
The atomic mass is a weighted average of the masses of all naturally occurring isotopes of the element
Takes into account that not all isotopes are found equally on earth

39. Section 2: The Atom Calculating the mass of an element Steps
There are two different isotopes of copper
Copper-63 (69% of earth’s copper is this type)
Copper-65 (31% of earth’s copper is this type
Steps
Convert percentages into decimals
Multiple decimal value by atomic mass
Add these amounts together to find the mass

40. Section 2: The Atom Calculating the mass of an element Steps
There are two different isotopes of copper
Copper-63 (69% of earth’s copper is this type)
Copper-65 (31% of earth’s copper is this type
Steps
Convert percentages into decimals
69%  0.69
31%  0.31

41. Section 2: The Atom Calculating the mass of an element Steps
There are two different isotopes of copper
Copper-63 (69% of earth’s copper is this type)
Copper-65 (31% of earth’s copper is this type
Steps
Multiple decimal value by atomic mass
(0.69 x 63) = 43.47
(0.31 x 65) = 20.15

42. Section 2: The Atom Calculating the mass of an element Steps
There are two different isotopes of copper
Copper-63 (69% of earth’s copper is this type)
Copper-65 (31% of earth’s copper is this type
Steps
Add these amounts together to find the mass
( ) = amu

43. Section 2: The Atom You try! Steps
There are two different isotopes of chlorine
Chlorine-35 (76% of earth’s chlorine is this type)
Chlorine-37 (24% of earth’s chlorine is this type
Steps
Convert percentages into decimals
Multiple decimal value by atomic mass
Add these amounts together to find the mass

44. Section 2: The Atom Forces in Atoms
Four basic forces that are working even inside teeny atoms!
Gravitation Force
Electromagnetic Force
Strong Force
Weak Force

46. Section 2: The Atom Section Summary
Please answer the objectives on your objective summary sheet
Describe the size of an atom
Name and state information about the parts of an atom
Describe the relationship between number of protons and neutrons and atomic number
State how isotopes differ
Describe and calculate atomic masses
Describe the forces within an atom