Catalyst IN YOUR JOURNAL!1. What are the two subatomic particles found in the nucleus?2. What is the charge of a proton? An electron?3. How do you survive the zombie apocalypse?

End

Design an Experiment

• With your table:– Design an experiment

to distinguish humans from zombies in the video.

– Make sure to talk about how you will collect data and make a hypothesis for the experiment that you are about to run.

Connection to Atomic Theory

• What we know about the atom was discovered through scientific experiments.

• Without these experiments we would not be able to have our current model of the atom.

Lecture 1.2 – Development of Atomic Theory

Today’s Learning Targets

• LT 1.2 – I can explain the development of atomic theory incorporating the contributions of Dalton, Thomson, Rutherford, and Bohr.

Dalton’s Model of the Atom

J. J. Thomson

• First evidence for any subatomic particles.

• Made discovery in 1896.

+

+

+

+

+

+

+

+

-

-

-

-

-

-

-

-

J. J. Thomson’s Experiment

• Cathode-ray tube

Outline of Thomson’s Experiment

• Attached battery to cathode tube, saw beam form.

• Beam contained subatomic particles.• Put a positive magnet next to the beam

and it bent towards the magnet.• Put a negative magnet next to the beam

and it bent away from the magnet.

Table Work – What subatomic particle did he discover?

Thomson’s Discovery

• Thomson discovered the electron!• He discovered that atoms must contain

some negatively charged particles, which he called electrons.

• Tells us nothing about the location of the electron within the atom.

Plum Pudding Model

• Thompson proposed that electrons were balls of negative charge floating in a sea of positive charges.

SUMMARIZE

A Picture Says a 1000 Words

• With your table, make a drawing of Thomson’s experiment.

• Label the major components (cathode ray tube, magnets, etc.)

• Provide a brief explanation of how this led to the discovery of the electron and the plum pudding model of the atom.

• Be prepared to present your creation.

5 MINUTE BREAK

Fire at Will!

Ernest Rutherford

• Student of Thomson.• Disproved Plum

Pudding Model with Gold Foil Experiment

• Used alpha particles, which are small, positively charged particles.

Rutherford’s Experiment

• Shot positively charged alpha particles at a piece of gold foil.

• Most particles went straight through the foil.

• Small amount of the particles were deflected, but still went through

• An even smaller amount were bounced back

Justify – TPS

• Using Rutherford’s data below, make a hypothesis about what this data indicates.

Observations Proportion

Particles went straight through the foil

>98%

Particles went through foil, but were deflected at an angle

2%

Particles bounced off the gold foil 0.01%

Rutherford noted: “It was almost as if you fired a 15-inch shell into a piece of tissue

paper and it came back and hit you.”

What Rutherford’s Data Meant

• Most alpha particles went straight through because the atom is mostly empty space.

• Some alpha particles deflected because they came close to the electrons.

• The few alpha particles that bounced back were hitting the very small, but very dense positively charged nucleus.

Important Point #1

• The atom is mostly empty space. This is why most of the alpha particles went through

• The majority of the atom does not have anything in it.

Important Point #2

• The atom has very small, but very dense nucleus.

• Alpha particles that bounced back were coming into contact with nucleus.

• Alpha particles were deflected back because nucleus is positive.

Niels Bohr

• Refined Rutherford’s model of the atom with his discovery in 1913.

What Bohr Knew

• Shooting electricity through the hydrogen excited electrons, which produced colors.

• Color produced only for specific values• Problem – If electrons were free to roam,

then we should get all sorts of colors…

Bohr’s Solution

• Electrons are restricted to orbitals or energy levels; they are not free to roam the electron cloud!

The Modern Model

electron

neutron

proton

Rutherford’s space and nucleus

Dalton’s atom

Bohr’s energy levels

Thompson’s electrons

White Board Races

Question 1

• Who discovered the electron?

Question 2

• What was the instrument called that J.J. Thomson used in his experiment to discover the electron?

Question 3

• Who discovered the nucleus?

Question 4

• What was Rutherford’s experiment to discover the nucleus called?

Question 5

• What did Niels Bohr discover?

Question 6

• What did Bohr look at to discover orbitals?

Question 7

• When Bohr looked at the hydrogen lamp through his special equipment, what was the name of the spectrum of light he saw?

SUMMARIZE

Exit Ticket

Scientist Discovery How they discovered this?(EXPLAIN!)

Thomson

Rutherford

Bohr

Rate Yourself

• Based on the exit ticket and your current level of understanding, rate yourself 1 – 4 on LT 1.2

Closing Time• Homework 1.2 – Thomson, Rutherford, and

Bohr.