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 elementsFire, Earth, Water, and AirFor 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?