Ch. 4  Chemistry Notes

We will study chapters 4 & 5 together in this unit.

Topic: Atoms/Development of Atomic Theory/Atomic Structure

1.     Know, understand, and explain the historical development of atomic theory (including experimental designs and conclusions made)

2.     Explain the modern theories of atomic structure

The following people are important in the historical development of atomic theory.  You will need to be able to explain their contributions and theories and a time line of the events.

1.     Democritus   460-370 BC (See fig 4-2 on p.88)

·        Proposed that matter is composed of empty space through which atoms move

·        Atoms are solid, homogeneous, indestructible, indivisible; 

·        believed that matter is made of atoms (Atomos means cannot be divided);

·        different kinds of atoms have different sizes & shapes

·        Apparent changes in matter result from changes in the groupings of the atoms and not from changes in the atoms themselves

2.     Aristotle   384-322 BC (see fig 4-3 p. 89)

·        One of the most influential philosophers; Wrote extensively on many subjects;

·        Rejected the atomic theory of Democritus; d

·        Didn’t believe in empty space (nothingness)

·        Believed that the only 4 elements were earth, air, fire, water

 

3.      Dalton-1808   See Fig. 4-4 p. 89

·        Revived and revised Democritus’ ideas.

·        Based his theory on scientific research

·        Proposed that all matter is composed of atoms

·        All atoms of a given element are identical, having the same size, mass, and chemical properties. Atoms of a specific element are different from those of any other element.

·        Atoms cannot be created, divided into smaller particles, or destroyed.

·        Different atoms combine in simple whole-number ratios to form compounds.

·        In a chemical reaction, atoms are separated, combined, or rearranged.

·        He studied mass ratios & clearly explained the law of cons. Of mass

 

4.     Crookes (1879-ish)

·        Used vacuum tubes and discovered cathode rays (cathode ray tubes) which were used to study the electron

 

5.     JJ Thompson (1897)

·        Used the  cathode ray tubes to discover the electron

·        This proved Dalton wrong (Atoms cannot be divided into smaller particles)

·        Theorized about the structure of the atom (Plum Pudding Model)

 

6.     Millikan (1909)

·        Determined the charge and the mass of the electron

7.     Rutherford

·         famous Gold Foil Experiment 

·         Discovered the nucleus

·         Later credited for discovering the proton

·         his atomic theory described the atom as having a central positive nucleus surrounded by negative orbiting electrons.

·          This model suggested that most of the mass of the atom was contained in the small nucleus, and that the rest of the atom was mostly empty space.

·         Rutherford came to this conclusion following the results of his famous gold foil experiment. This experiment involved the firing of radioactive particles through minutely thin gold sheets and detecting them using detecting screens.

·         Rutherford found that although the vast majority of particles passed straight through the foil a few were deflected leading him to his theory that most of the atom was made up of 'empty space', but there was a dense positively charged nucleus existed in the center.  Thus, he discovered the nucleus. (His model is sometimes called the planetary model)

 

8.     Chadwick (1932)

·        Discovered the neutron

 

 


9.     Planck

10.                        Einstein

11.                        Bohr

 

12.                        De Broglie

13.                        Heisenberg

14.                        Schrodinger

 

Structure of the Atom (Ch. 4 , section3) SEE P. 98

 

Relative Mass

 Relative Charge

Protons

1

+1

Neutrons

1

0

Electrons

0

-1

 

How to read periodic table: http://www.classzone.com/books/earth_science/terc/content/investigations/es0501/es0501page06.cfm

Atomic # = # of protons

To find the # electrons:

#p = # e-  (assume a neutral atom)

To find the # neutrons subtract: 

Atomic mass                               #p + # n

                             -atomic #                                -  #p   

                             # neutrons                                    # n

 

Look at your Periodic Table-Answer the following: P.99 # 11-13

p.99 #11

 

# p

# n

#e

B

 

 

 

Rn

 

 

 

Pt

 

 

 

Mg

 

 

 

 

12. A neutral atom contains 66 electrons.  Which element is it?

13. An atom contains 14 protons.  Which element is it?

Isotopes p. 100-101

Def: Atoms of the same element having different numbers of neutrons.

Written as K-41  or  41K

·       At. Mass # is a weighted average of all the isotopes.

·       Unit: amu

To Calculate avg. atomic mass:

Mass of each isotope

x % abundance(convert to decimal)

=the contribution of each isotope

         

Then Sum the results.

Steps For each For each isotope:

·         Step 1: convert % abundance to a decimal

·         Step 2: multiply that decimal by the mass of the isotope

·         Then add up all of the mass contributions made by each isotope

 

Example (p. 100, 2nd paragraph):

Three isotopes of K are:

# protons and # neutrons in each isotope
 
K-39                K-40          K-41

19 p                19p            19p

20n                 21n            22n

% abundance

93.25%                   .0117%               6.7302%

39 x .9325= 36.3675

40 x .000117=.00468

41 x .067302=2.759382

Add them up   39.132 = weighted average atomic mass

 

·       See p. 103 Example problem:

·       Do p. 104 Practice Problems # 15-17

Answers to p. 104  Do Practice Problems # 15-17

# 15

B-10         10.013 x .198   =     1.982  amu

B-11         11.009 x .802   =    8.829  amu    

                                                    10.81 amu            

#16 He-4

 

#17       

23.985 x .7899=   18.9457515

24.986 x.10     =       2.4986

25.982 x  . 1101=    2.8606182

                                   24.31 amu