DO NOW How do you know what wind is? Objective: Describe ancient Greek models of matter and explain how Thomson and Rutherford used data from experiments to produce their atomic models.

How do you know what the wind is?  Even though you can not see the wind, you know it is there.  Feel it, see leaves moving.  Atoms can not be see either, even with a microscope.  Need to study how they react in order to have an idea of what they look like.  Can you keep cutting a piece of aluminum foil into smaller pieces? What will eventually happen if you keep cutting it?

Ancient Greek Models of Atoms  Democritus- believed that all matter consisted of small particles that could not be divided  Called the particles atoms from the Greek word “atomos” for uncut  Different types of atoms with properties specific to the type of object (liquids atoms were smooth and solid atoms were rough and hard)

Ancient Greek Models of Atoms  Aristotle- did not think there was a limit to how many times an object could be divided.  Thought all substances were built from 4 elements Fire, Earth, Water, and Air For many centuries most people agreed with Aristotle

What is in the Bag??????  Get into groups.  Feel the object that is in the bag through the bag…. Do NOT open the bag, do NOT look in the bag  Write what you think is in each bag on a piece of paper.

John Dalton  John Dalton- born in 1766 in England  Was a teacher in England who spent his spare time doing experiments  Liked to predict the weather  Studied the behavior of gas in the air  Based on the way gases exert pressure, concluded that gas consists of individual particles  Dalton gathered evidence for atoms by measuring the masses of elements that combined to form compounds.  Found that no matter the compound the ratio of the masses of the elements is always the same

Evidence for atoms  Stated that compounds have a fixed composition  For example: when magnesium burns it forms magnesium oxide-  A 100g sample of magnesium will combine with 65.8g of Oxygen  A 10g sample of magnesium will combine with ______g of Oxygen.  6.58g

Dalton’s Atomic Theory  ALL MATTER IS MADE UP OF INDIVIDUAL PARTICLES CALLED ATOMS, WHICH CANNOT BE DIVIDED.  All elements are composed of atoms  All atoms of the same element have the same mass, and atoms of different elements have different masses.  Compounds contain atoms of more than 1 element  In a particular compound, atoms of different elements always combined in the same way.  Model was a solid sphere and each element had a different mass  Later science has found some ideas in the atomic theory incorrect but instead of discarding the theory, they revised it.

DO NOW  What were some of the main points of Dalton’s Atomic Theory?  All elements are composed of atoms  All atoms of the same element have the same mass, and atoms of different elements have different masses.  Compounds contain atoms of more than 1 element  In a particular compound, atoms of different elements always combined in the same way.  Objective: Explain how Thomson and Rutherford used data from experiments to produce their atomic models.

Thomson’s Model of the Atom  When objects repel or attract each other- they have a positive or negative electrical charge.  Like charges-repel  Opposite charges- attract  Demo- blow up a balloon and rub it on someone's hair  A flow of charged particles is called an electric current  Thomson used electric current to learn more about the atom

Thomson’s experiments  Used a sealed glass tube that had most of the air removed from it and metal disks on either end of the tube.  Wires connected to metal disks and source of electric current.  When current is turned on = one disk became positively charged and one became negatively charged. =A glowing beam appeared in the space between the disks

Thomson’s experiments (con’t)  Hypothesis: beam was a stream of charged particles that interacted with the air in the tube and caused it to glow.  To test hypothesis he put 2 more metal plates on the outside of the tube.  Result: beam deflected from its straight line towards the positive plate and away from the negative plate on the sides

Evidence for Subatomic Particles  Conclusion: particles in beam were negatively charged because they were attracted to the positive plate  Hypothesized that particles came from inside the atom.  Evidence:  Using different types of metal plates gave same results  No matter what metal Thomson used, the particles were always about 1/2000 of the mass of a hydrogen atom.  Thomson’s experiment provided the first evidence that atoms are made of even smaller particles

Thomson’s Atomic Model  Also known as the plum pudding model  Thomson said that if an atom is neutral and contains negative particles it must also contain positive particles  The negative particles are evenly spaced among the positive particles to make a neutral atom

DO NOW  What two pieces of evidence did Thomson find that supported his idea that subatomic particles existed?  Using different types of metal plates gave same results  No matter what metal Thomson used, the particles were always about 1/2000 of the mass of a hydrogen atom.  Objective: Explain how Thomson and Rutherford used data from experiments to produce their atomic models.

Rutherford’s Atomic Theory  Discovered uranium emits fast-moving particles that have a positive charge  Named them alpha particles  Wanted to know what happened to the particles when they were shot through a thin sheet of gold  Rutherford hypothesized that if the model of the atom was correct then shooting alpha particles at a thin sheet of gold would result in the alpha particles going straight through the sheet and light up the screen surrounding the gold sheet and some particles would deflect slightly

Gold Foil Experiment  There was a screen set up around a piece of gold foil that would light up if an alpha particle hit it.  Rutherford’s student shot narrow beams of alpha particles at the gold foil and recorded their path based upon where the screen flashed.  When the alpha particle was shot and the screen light up, the path of the alpha particle could be traced.  More particles were deflected than was predicted, some more than 90 degrees and some bounced right back where they came from, not just straight through as predicted.

The Gold Foil Experiment

Discovery of the Nucleus  Deflected particles came close to another charged object  Rutherford concluded that since some alpha particles went straight through while others were deflected, the positive particles were not evenly spread out through the atom but concentrated in the center.  Nucleus- small, dense, positively charged mass in the center of the atom  The alpha particles whose paths were deflected by more than 90 degrees came very close to the nucleus (like charges repel) and those than went straight through went through the space surrounding the nuclei

Shoebox Experiment  Each group will roll a marble through the openings of the shoebox.  Based on how the marble comes out of the box, the group will draw a picture of the shape of the wood under the shoebox.  Do NOT look under the shoebox until the lab is over.  Write a conclusion: How was this activity similar to what scientists have done in order to determine the shape of an atom?