Presentation is loading. Please wait.

Presentation is loading. Please wait.

The History of the Atom History of the Atom Timeline Democritus 460 BC and Dalton 1803 AD Thomson 1897 Rutherford 1912 Bohr 1913 Modern Quantum Cloud.

Similar presentations


Presentation on theme: "The History of the Atom History of the Atom Timeline Democritus 460 BC and Dalton 1803 AD Thomson 1897 Rutherford 1912 Bohr 1913 Modern Quantum Cloud."— Presentation transcript:

1

2 The History of the Atom

3 History of the Atom Timeline Democritus 460 BC and Dalton 1803 AD Thomson 1897 Rutherford 1912 Bohr 1913 Modern Quantum Cloud Model post 1930

4 Marble Model Plum Pudding Model The Nuclear Model The Planetary Model

5 Black Boxes Black Boxes are anything that you cannot see inside Like a cell phone… Or a locked box… Or an atom…

6 THE GREEK ATOM Democritus (around BC.), "a-tomos" and signifies "indivisible". 1.All matter is composed of indivisible atoms, which are too small to be seen. 2.There is a void, which is empty space between atoms. 3.Atoms are completely solid. 4.Atoms are homogeneous, with no internal structure. 5.Atoms are different in their size, their shape and their weight.

7 Early Greek Philosophers The ancient Greeks (~450 BC) believed there only four elements: Earth Air Water Fire

8 Aristotle The idea of the atom was strongly opposed by Aristotle and others. All substances were combinations of elements and elemental qualities. Fire, water, earth, and air. The atom receded into the background.

9 John Dalton ( ) Democritus’ idea of the atom was largely ignored until an English schoolteacher did some experiments over 2000 years later, he was… Leading to his atomic theory…

10 Dalton’s Atomic Theory (1803) 1.All matter is made up of small indivisible atoms. 1.All atoms of one element are alike, but they are different from atoms of other elements 1.In compounds, atoms join in whole number ratios. (Law Definite Proportions- Proust) 1.Atoms are neither created nor destroyed in any chemical reaction. (Law of Conservation of Mass- Lavoisier) 1.In chemical reactions, atoms are combined, separated, or rearranged.

11 Dalton's Atomic Theory 1. All matter is made up of small indivisible atoms. 10

12 Dalton's Atomic Theory 2. All atoms of one element are alike, but they are different from atoms of other elements 11

13 Dalton's Atomic Theory 3. In compounds, atoms join in whole number ratios. (Law Definite Proportions- Proust) 12

14 Dalton's Atomic Theory 4. Atoms are neither created nor destroyed in any chemical reaction. (Law of Conservation of Mass- Lavoisier) 5. In chemical reactions, atoms are combined, separated, or rearranged. 13

15 John Dalton’s Atomic Theory Almost right. A good start. 14 Structure of the atom after Dalton (ca. 1810) very small

16 Thomson’s Cathode Ray Tube Experiments and the Discovery of the Electron

17 JJ Thomson ( ) Thomson used the cathode ray tube to help establish the identity of the electron Click here to listen to him talk about it Gives off electronsVacuum Magnet - redirected the electrons- nobody knows why the magnetic field bends

18 17 J.J. Thomson (1897): Cathode Rays Atoms subjected to high voltages give off cathode rays.

19

20 But, what was that green light? Was it a light? Was it a particle? To test this, he brought a magnet close to the cathode ray tube to see what would happen.

21 20 J.J. Thomson: Cathode Rays Cathode rays can be deflected by a magnetic field. Cathode rays are negatively charged particles (electrons). Electrons are in atoms.

22

23 So, the magnet caused the cathode ray to move. What does that tell us? Would a magnet affect a light from a flashlight? (you could try this at home) Probably not. Therefore,! the cathode ray must be a particle

24 Thomson also noticed… That the cathode ray was coming out of the negative end (cathode) of the tube and going toward the positive end (anode) Therefore, because opposites attract, he concluded that the cathode ray must be negative He called these particles… Negative end Positive end

25 ELECTRONS! The discovery would alter Dalton’s model of the atom because now there is something inside it But, in addition to the negatively charged electrons, there must be something giving it a positive charge because the overall charge of the atom is neutral (not negative) Let’s look at Thomson’s model of the atom…

26 Original Model of the Atom Plum Pudding Model These newly discovered electrons must have been balanced by some sort of positive charge. Thomson proposed a 'plum pudding' model, with positive and negative charge filling a sphere. Even Thomson's student Rutherford, who later proved model incorrect, believed it at the time.

27 Thomson’s Plum Pudding Model of the Atom He believed the atom was made of positively charged stuff with negatively charged particles scattered throughout Why the “plum pudding” model? What is “plum pudding”?

28 An American analogy to his atom would be… Plum Pudding is an English dish sort of like bread pudding with raisins in it. …Is like… But we’ll still refer to it as the “Plum Pudding” model in class

29 28 J.J. Thomson – The Electron Structure of the atom after Thomson (ca. 1900) “Plum pudding” model: Negative electrons are embedded in a positively charged mass. Positively charged mass Electrons (-) Unlike electrical charges attract, and that is what holds the atom together.

30 Rutherford and the Nucleus

31 Ernest Rutherford New Zealand physicist ( ) In 1909, Rutherford performed the Gold Foil Experiment. In it, he shot alpha particles (very small, very dense, very fast particles) at a thin layer of gold foil.

32 Radioactivity Three types of radiation were discovered by Ernest Rutherford: –  particles (positive, charge 2+, mass 7400 times of e - ) –  particles (negative, charge 1-) –  rays (high energy light) 31

33 He expected all of the alpha particles to go straight through It would be like if you were shooting bullets at a cake…all of the bullets (or alpha particles) would go straight through the cake (or gold foil atoms)

34 33 Ernest Rutherford (1909) Scattering experiment: firing alpha particles at a gold foil

35

36 Rutherford’s Gold Foil Experiment Expected- particles to go straight through the plum pudding with its diffuse positive charge Actual- some particles bounced back! 1 in 8000,

37 Most of the alpha particles went straight through but a very tiny amount were deflected at odd angles? That could only happen if there was something very tiny in the atom that was dense enough to deflect the alpha particles. Like this…

38 Rutherford’s Reaction The amazed Rutherford commented 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."

39 The Nuclear Atom Some alpha particles bounce off the gold foil. This means the mass of the atom must be concentrated in the center and is positively charged! Thomson’s model could not be correct. 38

40 DISCOVERY OF THE NUCLEUS Rutherford proved that an atom was mostly empty space with a very small, very dense, positively charged nucleus in it. Rutherford Video

41 40 Ernest Rutherford The Nucleus and the Proton Structure of the atom after Rutherford Planetary Model (published 1911) The mass is not spread evenly throughout the atom, but is concentrated in the center, the nucleus. Electrons (-) are now outside the nucleus. The positively charged particles in the nucleus are protons.

42 DISCOVERY OF NUCLEONS Rutherford understood that the nucleus is itself composed of nucleons. These nucleons are of two types: positively charged, it's a proton. neutrally charged, it's a neutron The neutron was effectively discovered in 1932 by Chadwick.

43 42 James Chadwick – The Neutron Structure of the atom after Chadwick (1932) In the nucleus with the protons are particles of similar mass but no electrical charge called neutrons. Electrons (-) are now outside the nucleus in quantized energy states called orbitals. (From Niels Bohr and quantum mechanics) The positively charged particles in the nucleus are protons. n n +

44 BOHR ATOM In order to take account of atomic stability, Danish physicist, Niels Bohr created a new model of the atom in

45 BOHR ATOM The orbits of the electrons can't be just anywhere but are "quantified”; only certain particular orbits are permitted for the electron. It's not until one jumps from one orbit to another that it can emit (or absorb) light.

46 Modern Atomic Model Also known as the quantum atomic model. Describes the atom as mostly empty space with a tiny massive nucleus with protons and neutrons at the center. Surrounding the nucleus is a cloudlike region of electrons moving too fast to describe their location in space and time.

47 46 Structure of the Atom proton (+) neutron nucleus - responsible for the mass of the atom, positively charged electrons - responsible for the volume and size of the atom, negatively charged m m

48 What is the relative size of the atom….? An atomic model the size of Busch Stadium would contain a pea sized nucleus containing 95.95% of the atoms mass.An atomic model the size of Busch Stadium would contain a pea sized nucleus containing 95.95% of the atoms mass. The pea at the pitcher’s mound would be the nucleus, and a firefly flying around outside would be an electron!The pea at the pitcher’s mound would be the nucleus, and a firefly flying around outside would be an electron! The atom is mostly…..The atom is mostly….. Empty space! Nothing!Empty space! Nothing!

49 Subatomic Particles Protons and electrons are the only particles that have a charge. Protons and neutrons have essentially the same mass. The mass of an electron is so small we ignore it. 48

50 History of the Atom Timeline Democritus 460 BC and Dalton 1803 AD Thomson 1897 Rutherford 1912 Bohr 1913 Modern Quantum Cloud Model post 1930

51 Marble Model Plum Pudding Model The Nuclear Model The Planetary Model


Download ppt "The History of the Atom History of the Atom Timeline Democritus 460 BC and Dalton 1803 AD Thomson 1897 Rutherford 1912 Bohr 1913 Modern Quantum Cloud."

Similar presentations


Ads by Google