Platinum and Nickel How did we get here? Copper Atoms Click here to find out how we see atoms like the ones shown on this page! http://www.youtube.com/watch?v=IN6xNuhmIMc http://www.youtube.com/watch?v=prKi2TI0TVw Blue- tin Red- silicon Green- lead Next Carbon atoms

ATOMIC THEORY Next

Scientists Cat Joke Democritus & Leucippus John Dalton Ancient Greeks J.J. Thomson Ernest Rutherford Niels Bohr Summary Video Atom Review Click on scientist to guide you through the PowerPoint. All green boxes are links. Use them to guide you!

Cat Joke! Scientist Home

Ancient Greeks (450 BC) Believed all matter was made of: Earth Fire Water Air Scientist Home Cat Joke!

Cat Joke! Scientist Home

Democritus & Leucippus (300 BC) Experimental Conclusions Experiment New Model Scientist Home

Democritus & Leucippus Experiment They did not run any experiments. Atoms were an invention of their minds Democritus & Leucippus Next

Experimental Conclusions Atoms are the smallest particles of matter Defines the atom as the smallest particle Explains the existence of elements Democritus & Leucippus Next

Democritus & Leucippus Model Name: Atom the indivisible particle Description: Matter is made up of particles so small and indestructible that they cannot be broken down into smaller units- particles were called “atomos”, which is Greek from “indivisible” Democritus & Leucippus Model Shortcomings

Democritus & Leucippus Model Shortcomings No scientific view of the atom only a conceptual definition Does not talk about subatomic particles (electrons, protons, neutrons) Democritus & Leucippus Cat Joke!

Democritus & Leucippus Cat Joke! Democritus & Leucippus Scientist Home

Experimental Conclusions John Dalton (1800) Dalton Fun Facts  Scroll to them Experiment http://the-history-of-the-atom.wikispaces.com/John+Dalton Experimental Conclusions New Model Scientist Home

Experiment Dalton ran experiments with different types of gases and through deductive reasoning and experimentation he came to several conclusions. Dalton Next

Experimental Conclusions Pure Elements consist of particles called atoms. Atoms of an element are all the same for that element. That means gold is gold and oxygen is oxygen down to the last atom. Atoms of different elements can be told apart by their atomic weights. Atoms of elements unite to form chemical compounds. Atoms can neither be created or destroyed in chemical reaction. Dalton Next

Dalton’s Model Model Shortcomings Name: The Solid Sphere Model (Clay Ball Model) Description: Atoms are seen as solid, indestructible spheres (like billiard balls) Dalton Model Shortcomings

Model Shortcomings Atoms are not indivisible (b/c they are made up of subatomic particles) Atoms can change from one element to another by radioactive decay (not by chemical reactions). Not all atoms of the same element have exactly the same mass (isotopes). Dalton Cat Joke!

Cat Joke! Dalton Scientist Home

Experimental Conclusions J.J. Thomson (1850) Experimental Conclusions Experiment New Model Scientist Home

Experiment Experiment Animation Next http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::100%25::100%25::/sites/dl/free/0072512644/117354/01_Cathode_Ray_Tube.swf::Cathode%20Ray%20Tube Next

Summarized Experiment Detailed explanation of cathode ray tube Voltage Cathode (-) anode (+) http://electronics.howstuffworks.com/tv3.htm Click here Empty glass tube (vacuum) connected to a metal cathode and anode. High voltage is applied to the tube. This caused the atoms in the cathode to get excited. Electrons stream off the cathode, producing a cathode ray. The cathode ray traveled toward the anode Next

Summarized Experiment Voltage - Cathode (-) anode (+) Click here When a negative charge was brought toward the cathode ray, it caused the cathode ray to move away from the negative charge. Next

Summarized Experiment Voltage + Cathode (-) anode (+) Click here When a positive charge was brought toward the cathode ray, it caused the cathode ray to move toward the positive charge. Thomson Next

Experimental Conclusion Discovered the electron Electrons have negative charges Electrons are evenly distributed in a positive sphere. Thomson Next

Thomson’s Model Name: Plum Pudding Model Description: Atoms are solid spheres made up of a solid positive mass with tiny negative particles embedded in the positive core. Like a chocolate chip cookie! Cookie is positive Chocolate chips are negative electrons Thomson Next

Real Plum Pudding! Gross!! Thomson Model Shortcomings

Model Shortcomings Does not explain the existence of electrons outside the nucleus Does not explain the role of electrons in bonding Does not talk about neutrons, protons, or the nucleus Thomson Cat Joke!

Cat Joke! Thomson Scientist Home

Experimental Conclusions Ernest Rutherford (1905) Experiment Experimental Conclusions New Model Scientist Home

Experiment Experiment Animation Next http://www.learnerstv.com/animation/chemistry/ruther14.swf Next

Summarized Experiment Sent alpha particles (+2 charged Helium atoms) at a thin layer of gold foil He expected 100% of the particles to go through to screen 90% went through the foil to screen, but 10% were deflected He was surprised and wrote that this result was comparable with shooting a bullet at a piece of paper and having the shell reflected back. The plum pudding model could not be correct. Rutherford Next

Experimental Conclusion Detailed explanation of gold foil experiment Atoms are mostly empty space Atoms have a dense center with a positive charge called a nucleus Electrons move around the nucleus at a distance Detailed explanation of gold foil experiment http://science.howstuffworks.com/atom6.htm Rutherford Next

Rutherford’s Model Model Shortcomings Name: Nuclear atom Description: Positively charged nucleus in center of atom Electrons moving around nucleus at a distance Nucleus Electrons Rutherford Model Shortcomings

Model Shortcomings It does not explain: how negatively charged electrons keep from crashing into the positively-charged nucleus. Rutherford Cat Joke!

Cat Joke! Rutherford Scientist Home

Experimental Conclusions Niels Bohr (1920) Experiment Experimental Conclusions New Model Scientist Home

Experiment Experiment Animation An important experiment was the study of the emission of light by excited hydrogen atoms. http://www.colorado.edu/physics/2000/quantumzone/bohr.html Next

Experiment Summary Bohr Next When atoms receive energy, electrons move way from nucleus (higher energy level) When atoms release energy, electrons move toward nucleus (lower energy level) and release light Click for examples Energy Added Energy Released e- The resulting hydrogen atoms are excited; that is, they contain excess energy, which they release by emitting light of various wavelengths to produced emission spectrum of the hydrogen atom. e- Absorbs energy Releases energy

Experimental Conclusion Electrons can only exist on definite energy levels that are specific distances from the nucleus. Bohr Next

Bohr’s Model Model Animation Name: Planetary Model Description: Positively charged nucleus in center of atom Electrons moving around nucleus at specific energy levels (or distances from nucleus) Model Animation http://www.wwnorton.com/college/astronomy/studyspace/_animations/atomic_levels.htm Bohr Next Scientist Home

Summary of Atomic Theory Summary Animation http://glencoe.mcgraw-hill.com/sites/dl/free/0078600529/164155/00044672.html Scientist Home Atom Review

Na Atom Review +1 23 11 Mass number = #protons + # neutrons Atomic number = #protons= element Charge= #protons - # electrons Charge Na +1 23 11 Mass Number Atomic Number Nuclear symbol Next

C C C C Atom Review Mass number = #protons + #neutrons Average atomic mass = percent abundances of all the isotopes of an element 12 C 13 C 14 C The average atomic mass is on the periodic table: C 12.01 Next

Sample Average Atomic Mass Calculation Determine the average atomic mass of Ar if the isotopes are: 5% 79Ar and 95% 80Ar Step 1: convert % to decimal 0.05 and 0.95 Step 2: multiply decimal by mass number 0.05 X 79 = 3.95 0.95 x 80 = 76 Step 3: add values together 3.95 + 76 = 79.95 Step 4: check that the value matches the value shown under Ar on the periodic table Scientist Home