1. If you need a note-taking guide , please pick one up on the counter by the door

2. Scientists are people that like to use models.

3. Definition & Purpose of Scientific Models
What is meant by the scientific term “Model”?
A model is a visual representation of an idea, concept or structure.
What is the purpose of a “Scientific Model”?
A model is used to help make the concept, idea or structure more understandable.

4. Developing Scientific Models
Models are developed through the application of two types of Observations
Direct:
The observer is present during the event, witnessing it first hand.
Indirect:
The observer is not present during the event and must make inferences from the data present.
An inference is a conclusion made after considering all indirect evidence gathered.

5. Using Scientific Models
Give 2 examples of Models used in the following settings:
The Home:
Business & Technology:
Medicine:
The Science Classroom:

6. Using Scientific Models
Name 2 Careers that would use data/evidence gathered by using direct observations:
Name 2 Careers that would use data/evidence gathered by using indirect observations:

7. Hopefully, the following activity will help your understanding.
Scientific Models
How did scientists use indirect and direct observation skills to gather the data necessary to develop what we now accept as our current model of the atom?
Hopefully, the following activity will help your understanding.

8. ? The Mystery Tube Scientific Models
Observe the tests performed on the Mystery Tube and then describe & draw them using the handout provided.

9. Hypothesis #1
Scientist credited with discovery: ____________________

10. Hypothesis #2
Scientist credited with discovery: ____________________

11. Hypothesis #3
Scientist credited with discovery: ____________________

12. 1. ________________________________
Connections to the knowledge we now have about the atom:
The “Mystery Tube” is like studying the atom because…
1. ________________________________
2. ________________________________
3. ________________________________

13. Early Atomic Models
Atoms are so small they cannot be observed directly. Scientists can only use the data gathered experimentally making inferences using indirect observations.
Around 400 B.C., Democritus (a Greek philosopher) suggested that the world was made of two things, empty space and tiny particles called atoms.
During the 1800's, a French Chemist (Antoine Lavoisier) discovered that chemical "changes” occurring in a closed system - the mass after a chemical change was equal to the mass before the chemical change.

14. One of the first Atomic Models
The First formal Atomic Model (Aristotle & the Early Greeks, 390BC)
Air
Water
Earth
Fire

15. Four Element Theory Plato was an atomist (380BC)
Thought all matter was composed of 4 elements:
Earth (cool, heavy)
Water (wet)
Fire (hot)
Air (light)
Ether (close to heaven)
‘MATTER’
FIRE
EARTH
AIR
WATER
Hot
Wet
Cold
Dry
Relation of the four elements and the four qualities
Blend these “elements” in different proportions to get all substances

16. The Evolution of a Model

17. Democritus (400 B.C.)
Proposed that matter was composed of tiny indivisible particles
Not based on experimental data
Greek: atomos

18. Alchemy (approx. next 2000 years, (100BC -1800)
Mixture of science and mysticism.
Lab procedures were developed, but alchemists did not perform controlled experiments like true scientists.

19. Considered the “Father of the Atomic Theory.”
John Dalton (1807)
Considered the “Father of the Atomic Theory.”
British School teacher
based his theory on others’ experimental data
Billiard Ball Model
atom is a uniform, solid sphere

20. John Dalton, cont. Four Postulates of Dalton’s Theory:
1. Elements are composed of small indivisible particles called atoms.
2. Atoms of the same element are identical. Atoms of different elements are different.
3. Atoms of different elements combine together in simple proportions to create a compound.
4. In a chemical reaction, atoms are rearranged, but not changed.

21. John Dalton, cont.
Dalton stated a second law based on his own atomic theory but not based on experimental data. It concerns elements that form more than one compound with each other.
For example: Oxygen can combine in a 1:1 ratio by mass with Carbon to form Carbon Monoxide, CO, or a 1:2 ratio by mass to form Carbon Dioxide, CO2.
According to Dalton's second law, the ratio of masses of one element that combine with a constant mass of another element can be expressed in whole numbers (or %) - This statement is known as the Law of Multiple Proportions.

22. Henri Becquerel & Marie Curie, (1896)
Discovered radioactivity
spontaneous emission of radiation from the nucleus
Three types:
alpha () - positive
beta () - negative
gamma () - neutral

23. Particle I.D. using penetrating ability
Alpha Waves: Made of positive particles which can be stopped by paper.
Beta Waves: Made of negative particles which can be stopped by heavy clothing.
Gamma Waves: Made of very high non-particle radiation which can be stopped only by lead.

24. Gamma Rays More energy than x-rays; high frequency & short wavelength.
TYPES OF RADIATION:
If the structure of the nucleus is not stable, the nucleus will begin to decompose by ejecting a particle of energy until it reaches a more stable arrangement.
Alpha Rays Consist of 2 protons and 2 neutrons with no electrons (positively charged), the are made up of Alpha particles which have a speed of one-tenth the speed of light.
Beta Rays
Electrons with higher kinetic energy than electrons emitted by Cathode Ray Tubes. They are composed of neutrons which have changed to a proton & an electron.
Gamma Rays More energy than x-rays; high frequency & short wavelength.

25. Albert Einstein, (Early 1900’s)
Explained the origin of the energy released during nuclear changes.
Einstein hypothesized that there is energy contained within the matter contained in the nucleus of every atom. This statement can be expressed in the famous equation:
E = mc2
E = energy (in joules) m = mass (in kilograms) c = the speed of light (meters/second)

26. J. J. Thomson (1903) Cathode Ray Tube Experiments Discovered Electrons
beam of negative particles
Discovered Electrons
negative particles within the atom
Plum-pudding Model

27. J. J. Thomson (1903)
Experiments by several scientists in the middle 19th century led to the conclusion that the atom was made up of several smaller particles. With the use of a device called a Cathode-Ray tube it is possible to see these particles.

28. J. J. Thomson (1903)
In each end of the tube there is an electrode. When connected to a source of high voltage electricity, the electrodes become charged.
The positive electrode is called the anode. The negative electrode is called the cathode.

29. The Cathode Ray Tube

30. The Cathode Ray Tube Beam
Careful observations revealed rays produced inside the tube. Because the rays appeared to begin at the cathode and travel toward the anode, the rays were called cathode-rays.
Beam
Cathode ray tubes are used as “picture tubes” in televisions and computer monitors.

31. The Cathode Ray Tube Beam
Cathode ray tubes with a fluorescent screen at one end would glow. Thomson measured the deflection of the beam. A Magnet deflected the beam in one direction and a plate attracted the beam after it was deflected.
Beam

32. The Cathode Ray Tube Beam
Looking at the diagram above, what do you think Thompson concluded about the composition of the beam?
The beam was made of negative particles (electrons).

33. The Cathode Ray Tube
Thompson’s experiment showed that the deflection of a charged particle was dependent upon:
The mass of the particle.
The speed of the particle.
The electrical charge of the particle.
The strength of the magnetic field
The amount of charge on the plates

34. The particles in the cathode-ray tube were identical to one another.
Regardless of the type of gas or metal used in cathode-ray tube, the ratio of charge to mass remained the same. Therefore, what do you think he concluded?
The particles in the cathode-ray tube were identical to one another.
The symbol for the electron is e- , indicating that the electron has a negative charge.

35. The Cathode Ray Tube
Thomson also observed the following when he used hydrogen gas and high voltage with low pressure in cathode-ray tube - he noticed that two beams (one negative) and another beam moving in the opposite direction toward the cathode - a positive beam.
Thomson found that the deflection of the beam varied with different gases. Hydrogen ions had the greatest deflection, therefore the smallest mass.
A Proton is a positively charged particle found in all atoms possessing a +1 charge.

36. The Cathode Ray Tube

37. J. J. Thomson (1903) Plum-pudding Model
positive sphere (the pudding) with negative electrons (the plums) dispersed throughout.

38. Ernest Rutherford (1911) Gold Foil Experiment Discovered the nucleus
dense, positive charge in the center of the atom
Nuclear Model

39. Rutherford’s Gold Foil Experiment
Alpha particles (in a beam) are shot at gold, platinum, copper, and tin foil with a fluorescent screen around the sheet of foil and found that:
Most particles went straight through the foil.
Some particles paths were altered but still went through the foil.
Some particles were deflected and headed right back at the source.
What can be concluded by these results?

40. Isotopes and Atomic Number
While working with Neon, Thomson observed what seemed to be two kinds of neon atoms. They were exactly alike chemically, but different in their masses. Atoms of the same element that differ in mass are called Isotopes. Isotopes have the same number of protons but a different number of neutrons which accounts for the difference in their masses.

41. Isotopes and Atomic Number
The number of protons determines the identity of the element and the number of neutrons determines the isotope of the element.
The number of protons found in the nucleus is equal to the atomic number of the element.

42. Isotopes and Atomic Number
The total number of protons and neutrons is called the mass number ( = to atomic mass) of that atom.
To find the number of neutrons in an atom: (Atomic mass - Atomic number) = # Neutrons
Unstable Isotopes are radioactive.

43. Ernest Rutherford (1911) Nuclear Model
dense, positive nucleus surrounded by negative electrons

44. Niels Bohr (1913) Bright-Line Spectrum Energy Levels Planetary Model
tried to explain presence of specific colors in hydrogen’s spectrum
Energy Levels
electrons can only exist in specific energy states
Planetary Model

45. Niels Bohr (1913) Bright-line spectrum Planetary Model
electrons move in circular orbits within specific energy levels

46. Erwin Schrödinger (1926) Quantum mechanics Electron cloud model
electrons can only exist in specified energy states
Electron cloud model
orbital: region around the nucleus where e- are likely to be found

47. Electron Cloud Model (orbital model)
Erwin Schrödinger (1926)
Electron Cloud Model (orbital model)
dots represent probability of e- location, not actual electrons

48. James Chadwick (1932) Discovered neutrons Joliot-Curie Experiments
neutral particles in the nucleus of an atom
Joliot-Curie Experiments
based his theory on their experimental evidence

49. Revision of Rutherford’s Nuclear Model
James Chadwick (1932)
Neutron Model
Revision of Rutherford’s Nuclear Model

50. Quantum
Theory

51. Quantum Model Animation
Current Quantum Model
Quantum Model Animation

52. Result of the collective work of many scientists
Current Quantum Model
2s Orbital
1s Orbital
Nucleus
2p Orbital
3s Orbital
Electron Cloud
Quantum Model
Result of the collective work of many scientists

53. Gellmann’s Quarks (Murray Gellmann, 1969)
Current Quantum Model
Gellmann’s Quarks (Murray Gellmann, 1969)
Smaller particles making up protons

54. Quantum Mechanical Theory
Summary of our current understanding of the Atom
Atom is mostly empty space.
Dense nucleus containing protons & neutrons; nucleus has a net + charge.
Electrons found in the “cloud” surrounding the nucleus; location determined by probability based on electron density.
Electrons are located in quantum (energy) levels and in orbitals within each quantum level.
Shape & size of the atom is determined by the orbitals found within the atom.
This is shown (supported) by the periodic table.