1. Investigating Atoms and Atomic Theory
HISTORY OF THE ATOM
AND ATOMIC THEORY

2. Atomos: Not to Be Cut

3. Atomic Models
This model of the atom may look familiar to you. This is the Bohr model. In this model, the nucleus is orbited by electrons, which are in different energy levels.
A model uses familiar ideas to explain unfamiliar facts observed in nature.
A model can be changed as new information is collected.

4. The atomic model has changed throughout the centuries, starting in 400 BC, when it looked like a billiard ball →

5. Who are these men?
In this lesson, we’ll learn about the men whose quests for knowledge about the fundamental nature of the universe helped define our views.

6. Democritus
400 BC
This is the Greek philosopher Democritus who began the search for a description of matter more than 2400 years ago.
He asked: Could matter be divided into smaller and smaller pieces forever, or was there a limit to the number of times a piece of matter could be divided?

7. Atomos
His theory: Matter could not be divided into smaller and smaller pieces forever, eventually the smallest possible piece would be obtained.
This piece would be indivisible.
He named the smallest piece of matter “atomos,” meaning “not to be cut.”

8. Atomos
To Democritus, atoms were small, hard particles that were all made of the same material but were different shapes and sizes.
Atoms were infinite in number, always moving and capable of joining together.

9. This theory was ignored and forgotten for more than 2000 years!

10. Why?
The eminent philosophers of the time, Aristotle and Plato, had a more respected, (and ultimately wrong) theory.
Aristotle and Plato favored the earth, fire, air and water approach to the nature of matter. Their ideas held sway because of their eminence as philosophers. The atomos idea was buried for approximately 2000 years.

11. 500BC-1720 Alchemists
Now, they wanted to live forever, so they started out with trying to make a potion that could make them live forever. They didn’t succeed, but they did make many experiments, and the scientific method. They also kept careful records.

12. 1777 Antoine Lavoisier
He had the first version of the Law of Conservation of Matter. He also named oxygen and hydrogen. He invented the first periodic table, which had 33 elements.

13. 1780 Charles Augustin de Coulomb
He had the theory of Simple Machines. He also had Coulomb’s law which stated the interaction between electric charges. He also published the laws of friction. He used windmills and the elasticity of fibers and metals to come up with this law.

15. Dalton’s Model
In the early 1800s, the English Chemist John Dalton performed a number of experiments that eventually led to the acceptance of the idea of atoms.

16. Dalton’s Theory
He deduced that all elements are composed of atoms. Atoms are indivisible and indestructible particles.
Atoms of the same element are exactly alike.
Atoms of different elements are different.
Compounds are formed by the joining of atoms of two or more elements.

17. .
This theory became one of the foundations of modern chemistry.

18. 1879 Sir William Crookes
He came up with thallium and helium. He investigated canal rays, cathode rays, and plasmas. He used electricity in gases, and found as the pressure went down, the electrodes began to emit rays.

19. 1896 Becquerel
He came up with radioactivity. He found this out from unknown x-rays waves, which were produced by uranium. Penetrating radiation was also discovered by Becquerel. He also discovered that uranium was able to expose a photographic plate on black paper, and didn’t depend on the chemical state.

20. 1895 W.K. Roentgen
He discovered x-rays when he was working with Sir William Crooke’s tube. He also found that x-rays pass through different materials at different temperatures. He was doing an experiment on cathode rays, when he messed up and discovered x-rays.

21. Thomson’s Plum Pudding Model
In 1897, the English scientist J.J. Thomson provided the first hint that an atom is made of even smaller particles.

22. 1897 Plum Pudding Model
Discovered by J.J. Thomson. He said the atom was a sphere of positive electricity, with negative particles throughout. This came around right after he discovered the electron.

23. Thomson Model
He proposed a model of the atom that is sometimes called the “Plum Pudding” model.
Atoms were made from a positively charged substance with negatively charged electrons scattered about, like raisins in a pudding.

24. Thomson Model
Thomson studied the passage of an electric current through a gas.
As the current passed through the gas, it gave off rays of negatively charged particles.

25. Thomson Model
Where did they come from?
This surprised Thomson, because the atoms of the gas were uncharged. Where had the negative charges come from?

26. Thomson concluded that the negative charges came from within the atom.
A particle smaller than an atom had to exist.
The atom was divisible!
Thomson called the negatively charged “corpuscles,” today known as electrons.
Since the gas was known to be neutral, having no charge, he reasoned that there must be positively charged particles in the atom.
But he could never find them.

27. 1898 Marie & Pierre Curie
They both picked up on Becquerel’s work on uranium, which lead them to find the elements radium and polonium. Though Marie went further with the radioactivity of elements, she didn’t get very far. All she said was, “they were somehow disintegrating over time and emitting radiation that exposed the plate.” ~ Marie Curie
Pierre went on to say that atoms might be composed of even smaller things.

28. 1900 Max Planck
He was the person who came up with the original quantum theory. To come up with this, all he did was research from pervious scientists and a little bit on his own, and then wrote a book on the quantum theory (the theory: the behavior or matter and energy in an atom). He also was looking at color changes from energy. He also made a math equation to help with this theory.

29. 1905 Albert Einstein
First, he found that nature and matter intertwine somehow, the theory of measurement came about from this. Second, he publish 5 papers on electrons. These contributed to the quantum mechanics. He said, “light consists of quanta, bundles of energy which behave somewhat like particles.” ~Albert Einstein

30. 1908 Robert Millikan
He was by far the most famous American scientist. He wanted to find the electrical charge of electrons. He measured water droplets, and that wasn’t successful, so he measured oil droplets, where all this proved electrons were negatively charged. He also was a professor for many years, and wrote many textbooks on chemistry.

31. Robert Millican
In 1907 performed the “oil Drop” experiment which determined the charge of an electron to be x coulombs.
Using the mass to charge ratio for electrons he determined the mass of an electron to be x g

32. 1908 Hans Geiger
He helped invent the Geiger Counter, and the Geiger-Marsden experiment led him to the discovery of the atomic nucleus. The counter was able to prove the Compton effect, because is detected the neutrons, electrons, and quanta.

33. Rutherford’s Gold Foil Experiment
In 1908, the English physicist Ernest Rutherford was hard at work on an experiment that seemed to have little to do with unraveling the mysteries of the atomic structure.

34. Rutherford’s experiment Involved firing a stream of tiny positively charged particles at a thin sheet of gold foil (2000 atoms thick)

35. Most of the positively charged “bullets” passed right through the gold atoms in the sheet of gold foil without changing course at all.
Some of the positively charged “bullets,” however, did bounce away from the gold sheet as if they had hit something solid. He knew that positive charges repel positive charges.

37. This could only mean that the gold atoms in the sheet were mostly open space. Atoms were not a pudding filled with a positively charged material.
Rutherford concluded that an atom had a small, dense, positively charged center that repelled his positively charged “bullets.”
He called the center of the atom the “nucleus”
The nucleus is tiny compared to the atom as a whole.

38. Rutherford
Rutherford reasoned that all of an atom’s positively charged particles were contained in the nucleus. The negatively charged particles were scattered outside the nucleus around the atom’s edge.

39. Bohr Model
In 1913, the Danish scientist Niels Bohr proposed an improvement. In his model, he placed each electron in a specific energy level.

40. Bohr Model
According to Bohr’s atomic model, electrons move in definite orbits around the nucleus, much like planets circle the sun. These orbits, or energy levels, are located at certain distances from the nucleus.

41. 1913 The Bohr Model
Niels Bohr discovered this atom. It shows a positively charged nucleus surrounded by electrons. This was mostly to explain the Rydberg formula. The Bohr model is a hydrogen model. It helps with the learning of the quantum theory.

42. 1913 Niels Bohr
Niels figured out the structure of the atom, and their radiations. He also discovered the principle of complementary. He introduced electrons from the book he wrote on the structure of the atom. He also started the basis of the quantum theory.

43. 1922 Planetary or Solar System Model
Both Rutherford and Bohr contributed into this model. Rutherford said the atom is mostly empty space with a nucleus that has a positive charge surrounded by negative electrons. Then Bohr said they circulate the atom.

44. 1920’s Electron Cloud Model
Discovered by Erwin Schrödinger and Werner Heisenberg. They said an atom consists of a dense nucleus and many proton and neutrons and is surrounded by electrons, but they all have different energy levels, and different charges.

45. Electron Cloud: A space in which electrons are likely to be found.
Electrons whirl about the nucleus billions of times in one second
They are not moving around in random patterns.
Location of electrons depends upon how much energy the electron has.

46. Electron Cloud:
Depending on their energy they are locked into a certain area in the cloud.
Electrons with the lowest energy are found in the energy level closest to the nucleus
Electrons with the highest energy are found in the outermost energy levels, farther from the nucleus.

47. Wave Model

48. 1926 Erwin Schrödinger
Erwin’s contributions were the wave mechanics and quantum mechanics. He wrote papers on wave mechanics, which lead him to the quantum mechanics. To find these theories out, he worked out math equations and used statistics.

49. The Wave Model
Today’s atomic model is based on the principles of wave mechanics.
According to the theory of wave mechanics, electrons do not move about an atom in a definite path, like the planets around the sun.

50. The Wave Model
In fact, it is impossible to determine the exact location of an electron. The probable location of an electron is based on how much energy the electron has.
According to the modern atomic model, at atom has a small positively charged nucleus surrounded by a large region in which there are enough electrons to make an atom neutral.

51. 1932 James Chadwick
James discovered the existence of the neutron. He found this out because when he was looking at alpha waves, bounced off, saying there was no charge in the neutron. He also used an experiment similar to this to help with the creation of the atomic bomb, and the fission and uranium 235.

52. 1938 Otto Hahn & Lise Meitner
While working in a lab, Otto Hahn discovered radiothorium, and then later discovered 5 more elements. He also discovered radioactive recoil. Lise Meitner was he partner when they discovered the isotope of protactinium. His biggest discovery was barium as a fission element. He combined results with Otto Frisch and they came up with nuclear fission. He was testing uranium and how it busted into lighter elements. Lise always studied radioactivity. She, herself, discovered the auger effect.

53. 1951 Glenn T. Seaborg
Glenn was best known for identifying and discovering elements that were heavier then uranium. He also isolated 10 elements. He also proposed the “actinides” in the element table. He discovered these elements just by separating different elements, and combining different elements.

54. 1964 Murray Gell-Mann & George Zweig
Murray Gell- Mann was an American physicist who received a Nobel Prize for his theory on elementary particles. He also found that all the elements of an atom are held together by quarks. To find this, he blasted high speed electrons into a hydrogen atom.
George Zweig proposed the existence of quarks. He thought of them as aces, because he guessed there were four quarks in every atom.
Now, in the same year, both these guys proposed the idea of quarks. They tested electrical charges, and that how the numbers for quarks came about.

55. Quarks
Quarks are one type of matter particle. Most of the matter we see around us is made from protons and neutrons, which are composed of quarks.
Quarks were first discovered in experiments done in the late 1960's and early 1970's.

56. Describe Quark
Three families of quarks are known to exist. Each family contains two quarks. The first family consists of Up and Down quarks, the quarks that join together to form protons and neutrons.
The second family consists of Strange and Charm quarks and only exist at high energies.
The third family consists of Top and Bottom quarks and only exist at very high energies.

57. Quarks
There are six quarks, but physicists usually talk about them in terms of three pairs: up/down, charm/strange, and top/bottom. (Also, for each of these quarks, there is a corresponding antiquark.) Be glad that quarks have such silly names -- it makes them easier to remember!

59. Quarks have the unusual characteristic of having a fractional electric charge, unlike the proton and electron, which have integer charges of +1 and -1 respectively. Quarks also carry another type of charge called color charge, which we will discuss later.
The most elusive quark, the top quark, was discovered in 1995 after its existence had been theorized for 20 years.

60. The naming of quarks
The naming of quarks...
...began when, in 1964, Murray Gell-Mann and George Zweig suggested that hundreds of the particles known at the time could be explained as combinations of just three fundamental particles. Gell-Mann chose the name "quarks," pronounced "kworks," for these three particles, a nonsense word used by James Joyce in the novel Finnegan's Wake:
"Three quarks for Muster Mark!"

61. In order to make their calculations work, the quarks had to be assigned fractional electrical charges of 2/3 and -1/3. Such charges had never been observed before. Quarks are never observed by themselves, and so initially these quarks were regarded as mathematical fiction. Experiments have since convinced physicists that not only do quarks exist, but there are six of them, not three.

62. Like social elephants, quarks only exist in groups with other quarks and are never found alone. Composite particles made of quarks are called
Although individual quarks have fractional electrical charges, they combine such that hadrons have a net integer electric charge.

63. The other type of matter particles are the leptons.
There are six leptons, three of which have electrical charge and three of which do not. They appear to be point-like particles without internal structure. The best known lepton is the electron (e-). The other two charged leptons are the muon() and the tau(), which are charged like electrons but have a lot more mass. The other leptons are the three types of neutrinos (). They have no electrical charge, very little mass, and they are very hard to find.

64. The Higgs boson was the last particle of the Standard Model to be discovered. It is a critical component of the Standard Model. Its discovery helps confirm the mechanism by which fundamental particles get mass. These fundamental particles of the Standard Model are the quarks, leptons, and force-carrier particles

65. 2. Question: What is Standard Model?

66. Greek X Dalton Thomson Rutherford Bohr Wave Indivisible Electron
Nucleus
Orbit
Electron Cloud
Greek X
Dalton
Thomson
Rutherford
Bohr
Wave