1. Part 1 History and Scientists Chemistry
Atomic Theory
Part 1
History and Scientists
Chemistry

2. Learning Objectives
TLW research and describe the historical development of atomic theory (TEKS 6)
TLW be introduced to the scientists behind the atomic theory (TEKS 3.F. & 6.A.)
TLW begin to describe the relationship among electrons, protons, neutrons, atomic number, mass number, and isotopes (TEKS 6A, 6B, 11A)

3. Anticipatory Activity
What’s in the Box? Lab – to be done prior to beginning lecture from this PowerPoint

4. Agenda I. Atoms – Building Blocks of Matter & Subatomic Particles
II. Mass of Atoms
III. Meet the Scientists and Learn About Their Discoveries
IV. Modern Day Atomic Theory

5. I. Atoms A. Building blocks of Matter
1. Everything is made up of atoms
2. Atom is Greek for indivisible
3. There are three major parts to the atom called subatomic particles

6. ATOM NUCLEUS ELECTRONS PROTONS NEUTRONS
B. Subatomic Particles
Ions – lose/gain electrons
Cation – positive
Anion -- negative
ATOM
NUCLEUS
ELECTRONS
equal in a neutral atom
PROTONS
NEUTRONS
NEGATIVE CHARGE
QUARKS
Atomic Number
equals the # of...
POSITIVE CHARGE
Isotope – same number of protons, different number of neutrons
NEUTRAL CHARGE
Most of the atom’s mass.

7. II. The Mass of Atom A. Protons 1. are positively charge
2. have a mass of 1.67 X kg
3. Found in the nucleus
B. Neutrons
1. Neutral
C. Electrons
1. are negatively charged
2. Have a mass of 9.11 X kg
3. Found orbiting outside the nucleus

8. To Put Nucleus Size in Perspective
If an atom were the size of this stadium, then its nucleus would be about the size of a marble

9. Something “Quarky” About Atoms
Quarks are fundamental matter particles that make up protons and neutrons
6 types – up, down, charm, strange, top, bottom
Only 2 (up and down) exist in protons and neutrons, others are unstable and randomly occur
We have yet to determine their mass
Quarks and electrons are considered to be the smallest units of matter in the universe
Discovered by Murray Gell-Mann in the late 1960’s

10. III. The Scientists and their Discoveries

11. Democritus
ATOM
Smallest particle

12. Democritus (Greek philosopher)
1. Date = 400 B.C
2. Discovery = Theorized the smallest unit of an element
3. Importance = gave the term and definition of atom

13. 4. Atom is Greek for “unable to divide”
5. Believed movement of atoms caused changes in matter he observed, but couldn’t prove it with evidence people would accept

14. Molecules made of atoms
John Dalton
Atomic Theory
Molecules made of atoms
British

15. a. Every element is made of atoms
John Dalton
1. Date = 1803
2. Discovery =
a. Every element is made of atoms
b. atoms of same element exactly the same
c. Atoms of different elements join together to form molecules
English

16. Importance = proposed the ATOMIC THEORY
Atomic Theory (in beginning) =
1. everything is made up of atoms
2. atoms make up molecules
3. atoms of the same element are the same
4. Atoms cannot be divided
5. in chemical reactions, atoms are combined,
separated, rearranged..
…. BUT NEVER destroyed
6. aka Law of Conservation of Mass

17. a. Order of elements is based on the
Dimitri Mendeleev
1. Date = ca. 1870
2. Discovery =
a. Order of elements is based on the
periodic law
b. Periodic Law states properties of elements will occur in a regular pattern
3. Importance =
First periodic table of elements…
….arranged by mass
Russian

18. Mendeleev’s Periodic Table

19. Eugen Goldstein 1. Date = 1886 2. Discovery =
a. discovered protons using cathode
ray tube. Rays were observed traveling
in the direction opposite of the
cathode rays.
b. protons are positive
3. Importance =
atoms have both negative and positive particles
Swiss  German

20. 4. How?
a. Using a cathode ray
b. relationship between electricity and matter
c. electric current was passed through
various gases at low pressure in a glass
tube = cathode
d. In Goldstein’s Experiment: Rays were
observed traveling in the direction
opposite of the cathode rays.
e. Later we’ll learn that In Thomson’s Experiment:
Cathode Rays were attracted to positive
electrical charges.

21. Discovery of the Protron
In 1886, Eugen Goldstein used a cathode ray tube to discover the presence of a positively charged particle called a proton.
Cathode ray tubes pass electricity through a gas that is contained at a very low pressure.

22. a. discovered metals contain negatively charged particles
William Crookes
1. Date = 1887
2. Discovery =
a. discovered metals contain
negatively charged particles
3. Importance =
early indication of the electron
British

23. Electrons are negative
J.J. Thomson
“Plum Pudding” model
Electrons are negative
British

24. J.J. Thomson
1. Date = 1898
2. Discovery =
a. discovered electrons
b. electrons are negative
3. Importance =
atoms have both negative and positive particles

25. Discovery of the Electron
In 1897, J.J. Thomson used a cathode ray tube to discover the presence of a negatively charged particle called an electron.
Cathode ray tubes pass electricity through a gas that is contained at a very low pressure.

26. a. hot objects don’t emit energy continuously, like in a wave
Max Planck
1. Date = 1899
2. Discovery =
a. hot objects don’t emit energy
continuously, like in a wave
b. instead, energy is emitted in small, specific amounts called quanta
3. Importance =
original idea of quantum theory
German

27. Electrons outside nucleus
Ernest Rutherford
Discovered nucleus
Electrons outside nucleus
Gold Foil Experiment
New Zealand born Brit

28. Ernest Rutherford
1. Date = 1911
2. Discovery =
a. discovered nucleus
b. did a “gold foil” experiment
c. atoms mostly made of space
3. Importance =
a. nucleus is very tiny, and positively charged
b. electrons outside of nucleus

29. Rutherford’s Gold Foil Experiment
Alpha particles are helium nuclei
Particles were fired at a thin sheet of gold foil
Particle hits on the detecting screen (film) are recorded

30. Try it Yourself!
In the following pictures, there is a target hidden by a cloud. To figure out the shape of the target, we shot some beams into the cloud and recorded where the beams came out. Can you figure out the shape of the target?

31. The Answers
Target #1
Target #2

32. Rutherford’s Experiment
As a follow up to our Introductory Activity of What’s in the Box?…
We will now conduct a simple experiment to determine the size and shape of an object by indirect means…. as did Rutherford when he developed Atomic Theory
See pages 45 & 46 in Chemistry Lab Manual (Prentiss Hall)
See IPC Manual pages 122 & 123

33. a. Radioactivity of isotopes 3. Importance =
Marie Skodowska Curie
1. Date = 1911
2. Discovery =
a. Radioactivity of isotopes
3. Importance =
paved way for use of radioactive isotopes in medical field and
other applications
Polish-French

34. technology to measure the number of protons in an atom
Henry Moseley
1. Date = 1913
2. Discovery = used x-ray
technology to measure the
number of protons in an atom
3. Importance = led to better
arrangement of Periodic Table by atomic number
(more on the PT later….)
English

35. a. measured the quantity of charge on the electron
Robert Millakan
1. Date = 1916
2. Discovery =
a. measured the quantity of charge
on the electron
b. determined ratio of charge to
mass of an electron
3. Importance = determined mass
of an electron
American

36. Discovery Education
Early Nuclear Theory

37. Niels Bohr
Electrons in energy levels (orbits)
Danish

38. Niels Bohr
1. Date = 1913
2. Discovery =
a. Electrons are in energy levels
b. s, p, d, f orbitals
c. 1st = 2 electrons;
2nd = 8 electrons;
3rd = 18 electrons
4th = 32 electrons

39. Energy Levels (more)
Fixed energy levels are analogous to rungs on a ladder
A person cannot stand between them, they climb from one to another to reach a greater height
Similarly, an electron cannot exist between energy levels
To jump from one energy level to another the electron must gain or lose energy

40. Quantums of Energy Have you heard of the term “quantum leap”?
A quantum of energy is the amount of energy required to move an electron from its present energy level to the next higher one.
The higher the electron is on energy ladder, the farther it is from nucleus

41. This is the Bohr Model 3. Importance =
electrons orbit around nucleus in a certain pathway like planets around the sun.
This is the Bohr Model

42. Bohr’s Model and What It Led To
Discovery Streaming VIDEO

43. 2. Discovery = only one electron can occupy a given quantum state
Wolfgang Pauli
1. Date = 1925
2. Discovery = only one electron can
occupy a given quantum state
3. Importance = determined how
electrons pair up and the direction of
their movement
Austrian-Swiss

44. Erwin Schrödinger Atoms have no charge
Same number of protons and electrons
Quantum Mechanical Model

45. Erwin Schrödinger
1. Date = 1926
2. Discovery = electrons are impossible to find (like moving
fan blades)
3. Importance =
a. Developed Quantum Mechanical
Model
b. Atoms are neutral
c. Atoms must have the same number of protons and electrons

46. Quantum Mechanical Model
Mathematically based
Does not define an exact path for electrons as did Bohr’s Model (orbitals)
Estimates the probability of finding an electron in a certain position
Sheldon from The Big Bang Theory sitcom explains Schrodinger’s Cat Model (YouTube)
Another YouTube video of Schrodinger’s Cat

47. determine position and momentum of a particle
Werner Heisenberg
1. Date = 1927
2. Discovery =
can’t simultaneously
determine position and
momentum of a particle
3. Importance = predicted better known
the position, less known of momentum
YouTube video on Heisenberg’s Uncertainty Principle
Another YouTube video on H’s Uncertainty Principle
German

48. James Chadwick
1. Date = 1932
2. Discovery = demonstrated existence of neutron
3. Importance = this accounted for the additional mass in the nucleus of an atom

49. IV. Modern Day Atomic Theory
1. All matter is composed of atoms
2. Atoms of different elements have different properties and masses
3. Atoms can combine in chemical reactions (law of conservation of mass)
4. Atoms can be divided
5. Elements of the same atom can have different masses
Called isotopes – more later

50. Projects Atomic Timeline -
For more on other contributors and exciting moments in atomic theory history click on this link
FactBook Page for Scientist - link

51. IV. Section Questions 1. Which “scientist” gave us the word atom?
2. Which scientist developed the atomic theory?
3. Every element is made of atoms, atoms of the same element are exactly the same, different atoms make up molecules. These statements make up the what?

52. 4. Which scientist discovered the electrons?
5. Which scientist discovered the nucleus?
6. Which scientist discovered that electrons were in energy levels?
7. Which scientist said atoms were neutral because they had equal number of protons and electrons?

53. 8. What is the mass of protons?
9. What is the mass of neutrons?
10. What is the mass of electrons?
11. Which part of the atom has the least amount of mass?

54. Review Key Points Atoms are building blocks for all matter
Name the subatomic particles
Name key scientists and their work in atomic theory
List the 5 points of modern atomic theory

55. Independent Practice Atomic Theory Timeline Project link or
Atomic Theorists FACTBook page link
Word Search – write the word with its definition on the back
Crossword Puzzle