BLOG POST ASSIGNMENT: HISTORY: DEVELOPMENT OF ATOMIC THEORY TIMELINE....

The following is a summary of our work from class last week. 

This study guide is a great tool that you will need for the essay portion of your UNIT TEST! However, please be advised that this timeline is NOT INCLUSIVE of all of the information or theorists that you need to know. 

This is simply a review based on responses given in class. There are a few KEY PEOPLE missing from this timeline that you are responsible for studying!

Your blog posting assignment this week is to find the missing theorists, summarize their work, and list where on the timeline they belong. 

P.A.T. (Preferred Activity Time) Points will be awarded to the first student who posts the correct answer. 

Atomic Theory Timeline: Democritus to the Quantum Model

Democritus

• 400 B.C.E.
• Believed that atoms were tiny indivisible particles. 

John Dalton

• 1808
• All matter is composed of extremely small particles called atoms. 
• Atoms of a given element are the same in size, mass and other properties; atoms of different elements differ in size, mass and other properties. 
• Atoms cannot be subdivided, created nor destroyed. 
• Atoms of different elements combine in simple whole-numbers rations to form chemical compounds. 
• In chemical reactions, atoms are combined, separated, or rearranged. 

J.J. Thomson

• 1897
• Cathode-ray tube experiments
• Discovered electrons

Ernest Rutherford

• 1911
• Gold-foil experiments with alpha particles
• Discovered positive core center of an atom

Neil Bohr

• 1913
• Electrons can circle the nucleus only in allowed paths, or orbits

Quantum Model

• 1924
• Electrons exhibit wave-like patterns, and the location of them can be mathematically determined. 

Thomson's Cathode Ray Tube

This is the original Cathode Ray Tube used by John Thompson at the University of Cambridge. See next post for Experiment information.

Rutherford's Gold Foil Experiment Part 2

This is the interpretation of what Rutherford saw. The results indicated that the alpha particles had struck something massive. Rutherford proposed that most of the mass of atoms was concentrated in their centers. This concentration of mass is now known as the nucleus.

An Overview Assignment

The following questions are designed to give you an idea of how well you know the material we have been covering in class. 

There are two, "Thinking It Over" sections of this assignment that are useful practice questions for the history portion of this unit. The remainder are more directly aimed at Dr. Jansen's class, however, a solid foundation of knowledge is indeed necessary for success in both courses! Good Luck! Try to do as much as you can without opening your textbook!

Section 1

Thinking It Over

1. a) Describe the following scientists and their contributions to atomic theory. Include a paragraph comparing or contrasting the two. 

    Democritus, 400 B.C.E.                     

    John Dalton, 1800s

b) How is a molecule different from an atom? 

2. Describe the following scientists and their contributions to atomic theory. 

     J.J Thompson                                       

(Be sure to include the words: beam, magnet, cathode, anode, neutral, electrons and, positive mass in your answer).

Ernest Rutherford and James Chadwick

(Be sure to include the words: alpha particles, gold foil, empty space, positively charged mass, nucleus, electrons, protons and, neutrons in your answer.) 

  

MATCHING SECTION:  

______ ATOMOS                            A. Has a positive charge. 

______ELEMENT                          B. The centre of an atom. 

______MOLECULE                        C. Holds the nucleus together. 

______NUCLEUS                           D. Has a negative charge. 

______PROTON                             E. Two or more atoms. 

______ELECTRON                         F. Has no charge. 

______ NEUTRON                         G. Greek for "indivisible". 

______ STRONG FORCE                H. Found on the periodic table. 

TRUE OR FALSE:  

1.____ The nucleus contains protons and neutrons. 

2.____ Atoms contain empty space. 

3.____ The chemical formula for water is H2O2. 

4.____ Electrons are found inside the nucleus. 

5.____ The atomic number tells you how many protons an atom has. 

6.____ The elements on the periodic table are arranged by the number of neutrons. 

7.____ Electrons are bigger than protons and neutrons. 

8.____ Electrons move near the speed of light. 

9.____ Different types of atoms can bond together to make molecules. 

ESSENTIAL VOCABULARY: 

Are you able to define these words? 

Elements: 

Atom:

Proton:

Neutron:

Electron:

Nucleus (in chemistry): 

The Strong Force:

Atomic Number:

Atomic Mass:

Molecule:

Alpha Particle: 

Electron Cloud: 

Rutherford's Gold Foil Experiment Part 1

A beam of positively charged alpha particles was directed at a very thin gold foil. A luminescent screen coated with zinc sulfide was used to detect particles passing through. Most of the particles passed through the foil, but some were deflected from their path. Some even deflected backwards.

Millikan Oil Drop Experiment

A fine mist of oil drops is introduced into a chamber. The gas molecules inside the chamber are ionized by a beam of x-rays. The electrons adhere to the oil drops, some having one electron, others having 2 and so on. These negatively charged droplets fall under the force of gravity into the region between the electrically charged plates. By adjusting the voltage on the plates, the force of gravity on the droplet is exactly counterbalanced by the attraction of the negative droplet to the upper, positively charged plate. Analysis of these forces led to a value for the charge on the electron.

JJ Thomson's Experiment

A beam of cathode rays, or particles, passes through an electric field and a magnetic field. The experiment is arranged so that the electric field causes the beam of particles to be deflected in one direction, and the magnetic field deflects the beam in the opposite direction. By balancing the effects of these fields, the charge-to-mass ratio of the particles can be determined. These negatively charges particles were later called Electrons.

UNIT TEST SOON

Attention students in Chem. Remember that our unit test is on March 30th and will cover the history of the atom. The test will include multiple choice questions, matching and short answer. Study Hard and Have fun doing it!