1. A Particulate World – Part I Day 9
Alchemy
A Particulate World – Part I
Day 9

2. Catalyst – 9/21 (page 14)
What are the five models of atomic theory? (in order)

3. Agenda Reminders Dead Chemists Lecture Pudding In The Clouds Activity
Graphic Organizer Time Line Guided Notes
Pudding In The Clouds Activity

4. Early Theories of Matter
Ancient Greeks: All matter consists of 4 elements:
Earth, Air, Water, & Fire

5. It's time for... Dead Chemists
Take notes on the Time Line Graphic Organizer

6. Cast of Characters 1. Democritus 2. Lavoisier 3. Proust 4. John Dalton
5. J.J. Thomson
6. Ernest Rutherford
7. James Chadwick
8. Niels Bohr
9. Robert Millikan
10. Ernst Schrodinger
New atomic Model

7. Democritus (2400 years ago)
Greek philosopher ( B.C.)
Atomos - “indivisible”.
The universe was made up of atoms.
Small & indestructible

8. Antoine Lavoisier (1743 - 1794) Law of Conservation of Mass - 1774
Father of Modern Chemistry

9. Joseph Proust The Law of Definite Proportions (composition) - 1808
In any compound the elements are present in a fixed proportion by weight.

10. John Dalton ( )
Atomic Theory
Law of Partial Pressures!

11. Dalton’s Atomic Theory
Wrong!
Elements are made of tiny particles called atoms that are indivisible..
All atoms of a given element are identical.
The atoms of a given element are different from those of any other element.
Atoms of one element can combine with atoms of other elements to form compounds. A given compound always has the same relative numbers and types of atoms.
Atoms are indivisible in chemical processes. That is ,atoms are not created or destroyed in chemical reactions. A chemical reaction simply changes the way the atoms are grouped together.
Wrong!

12. J.J. Thomson ( )
Discovered electrons (cathode ray tube experiment)
Developed “plum pudding” atomic model

13. Thomson’s Cathode Ray Tube Experiment
Results: The discovery of the electron! Atoms are divisible!
A CRT is an empty glass tube that has an electric current passed through it.
Thomson proposed that the mysterious rays in the tubes were pieces of atoms!
Remember –
up until this point,
the atom was it!
No protons, neutrons,
electrons, quarks, etc.

14. Thomson’s Plum Pudding Model
The atom is divisible!
Electrons are suspended in a positively charged electric field
Mass of atom due to electrons  
Atom mostly "empty" space compared size of electron to size of atom
Wrong!
Wrong!

15. Ernest Rutherford (1871-1937) Gold foil experiment
Rutherford’s atomic model
Discovered the nucleus
Atom is mostly space
Mass is concentrated in a positively charged nucleus (sort of discovered protons)

16. Rutherford’s Gold Foil Experiment
He bombarded a thin gold foil with alpha particles (He atoms).
Although almost all of them went through the gold, 1 in 8000 would "bounce" back.
Rutherford said that it was "as if you fired a 15-inch naval shell at a piece of tissue paper and the shell came right back and hit you."
He concluded that the atom's mass is concentrated in a small positively-charged nucleus and the electrons inhabit the farthest reaches of the atom.

17. There are protons and neutrons in Rutherford’s nucleus!
James Chadwick ( )
I discovered the neutron! And isotopes!
                                           
There are protons and neutrons in Rutherford’s nucleus!

18. Niels Bohr ( )
If electrons are stationary, they would fall into the positively-charged nucleus!
The electrons must be moving in planet-like orbits around the nucleus!
Wrong!

19. Bohr’s Atomic Model Electrons orbit in paths around nucleus
By assuming electrons orbited in circles with disscrete radii, Bohr could explain the discrete wavelengths in the emission spectrum of H.
Big Problem: It only worked for hydrogen!
Wrong!

20. More on the Bohr Model
The energy level is the region around the nucleus the electron is likely to be moving.
Quantum theory – a quantum of energy is the amount of energy required to move an electron from one energy level to another.

21. Robert A. Millikan ( )
Millikan found the charge of an electron through his famous oil drop experiment.
An electron has a charge of x coulombs.
                                           

22. Millikan’s Oil Drop Experiment
Oil droplets were sprayed into a small hole in a box with a metal top and bottom.
The metal was electrified, causing the oil droplet to be suspended in midair.
The voltage, speed, and mass of the droplet was used to calculate the electric charge of the electron.

23. Ernst Schrodinger ( )
Developed the quantum mechanical model of the atom
Can only calculate the probability of finding an electron in a certain position around the nucleus (energy levels).
Electron clouds are most dense where the probability for finding an electron is high.
Particles behave like waves.

24. Review
The 5 Basic Models:

25. Antiquity
Ancient Model through John Dalton

26. JJ Thomson
Plum Pudding Model

27. Rutherford
The nuclear or “nut” model.

28. Bohr
Planetary Model

29. Schrodinger
Quantum Mechanical Model

30. The Structure of the Atom
The Billiard Ball Model
Plum Pudding Model
Nuclear Atom
Bohr Model
Electron Cloud (Quantum Mechanical Model)

31. An Atom

32. Day 10
Isotopes and Building Atoms

33. Outside nucleus (electron cloud)
Subatomic Particles
Charge
Location
Mass
Neutron
Nucleus
1 amu
Proton +1
Electron -1
Outside nucleus (electron cloud)
1/2000 amu

34. Nucleus: Atom Marble: Stadium

35. All about the atom All neutrons are identical
All protons are identical
Electrons are identical, but have different energy levels
The nucleus is dense
The electron cloud is mostly empty space
In a neutral atom (not an ion):
# of electrons = # of protons

36. Atomic Number
The number of protons in the nucleus of an atom is called the atomic number.
Protons are what define an atom of an element.
So what is going on here?
                
                         
                            
Hydrogen
Hydrogen
(Deuterium)
Hydrogen
(Tritium)

37. What does “Carbon-12” mean?
Mass Number of an Atom
Mass Number = # Protons + # Neutrons
Carbon-12 has 6 neutrons and 6 protons, so its mass number is 12 amu.
Electrons have a teeny-tiny mass so they are not included in the mass number!
What does “Carbon-12” mean?

38. Building Atoms
Complete building atoms activity Questions 1 – 10 found on page 48 of your Alchemy Workbook.
Complete on page 16 of your Classwork NB

39. The Convenient Atomic Mass Unit
1 amu = 1.67 x g
How did we get it?
1 amu = 1/12 the mass of 1 C-12 atom.

40. Isotopes
An atom that has the same number of protons but a different number of neutrons is an isotope.
Example:
Carbon will always have 6 protons, but the number of neutrons can change.
Carbon-12 (6 protons + 6 neutrons)
Carbon-13 (6 protons + 7 neutrons)
Carbon-14 (6 protons + 8 neutrons)

41. Isotopes
Lithium-7
3 protons
4 neutrons
The 3 protons in the nucleus are what make this atom Lithium!
Mass # 7 Li
Symbol 3
Atomic #
Remember: Atomic # = # of protons

42. Another Isotope Example
ALL Bromine atoms have 35 protons.
Some have:
41 neutrons
42 neutrons
44 neutrons
46 neutrons
47 neutrons
48 neutrons
Mass # Br
Atomic #
How would you find the
number of neutrons?

43. Atomic Mass
Atomic mass (weight) is the weighted average of the mass numbers of the isotopes of an element.
Carbon’s average atomic mass is 12.01

44. Fill in the table! He 2 4 Mg 12 Br 80 35 Al 13 14 Symbol Atomic #
Mass #
# Protons
# Neutrons
# Electrons He 2 4 Mg 12 Br 80 35 Al 13 14

45. How did you do? He 2 4 Mg 12 24 Br 35 80 45 Al 13 27 14 Symbol
Atomic #
Mass #
# Protons
# Neutrons
# Electrons He 2 4 Mg 12 24 Br 35 80 45 Al 13 27 14

46. Ions
To be stable, some atoms will gain or lose electrons and become IONS.
Cations are positively charged (lose electrons)
Anions are negatively charged (gain electrons)
Lithium loses one electron to become Li+
Chlorine GAINS one electron to become Cl-