UNIT 2 – THE ATOM                          Lesson 2.1   Feb 28

The history of describing what things are made of,  “ the early study of matter” was not called chemistry.

Early Models of the Atom

1.           Greeks – philosophers, thinkers, ideas,

Democritus used the word “atomos” meaning indivisible

     Aristotle divided matter into earth, air, fire, water.

 

2.           Middle Ages (1400-1600)– “Alchemy”  … making metals like Gold from iron.   Using potions to heal people.  Impressing people with magical chemical reactions.

 

3.           Dalton (early 1800’s) – matter is made of atoms that are described as indivisible … balls, spheres, billiard balls..

 

Elements have only one kind of atom.

Did experiments with measuring compounds that broke up into elements…Proportionally.

 

 

Water  + (electricity)à       Hydrogen      +    Oxygen

10.2 g                                   3g                    7.2 g

 

Hydrogen Peroxide  à     Hydrogen     +   Oxygen

29 g                                     5 g                     24 g

 

Exp.1     O/H = 7.2  /  3 = 2.4

 

Exp. 2   O/H  = 24 / 5 = 4.8

 

Exp. 2 / Exp 1 =  4.8  / 2.4 =  2.     A whole number!

 

CONCLUSION:

 

Molecules are made up of atoms joined together

The Molecules of Compounds are made up of atoms in whole number ratios.

AB,  AB2 ,  AB3  ….

 

 

4.           Crookes, William  (l879)

Invented and worked with a vacuum tube with electricity running through it from one end (negative cathode) to the other end (positive anode).   At the positive end (shaped like a cross), there was a shadow left on a fluorescent screen.

 

http://micro.magnet.fsu.edu/electromag/java/crookestube/

 

Conclusion:  There are particles called electrons that move from the negative to positive electrodes through space.

 

 

 

5.            Thomson, J.J. (1897)

Worked with a version of the Crookes tube,

 called a Cathode Ray Tube (CRT)  (early TV monitor), controls a beam of electrons with magnets.

Measured…the deflection of a beam of electrons with a measured magnetic field and calculated the

Mass/charge ratio of electrons.

·                The atom consisted of positive charge with electrons  evenly distributed throughout it.

+ - + - +

-       +- + -

+ - + - +

(the raisin bun or plum pudding model, chocolate chip)

 

 

 

6.             Millikan, Robert (1909)

Worked with charged oil droplets and further proved the existence and mass of the electron.

 

7.           Becquerel, Henri (1896) -  observed the affect of invisible radiation coming from radium that exposed a film.

Called them X-rays.

 

8.           Rutherford (1911) –

 

·    Hmwk – describe his experiment and what it tells us about the atom.  Try to find a web site too.

 

By aiming a beam of particles (alpha) at a thin gold foil, he proved that atoms were mostly space.  The bouncing back of the occasional particle meant that the atom had a more solid centre (nucleus).

(see p. 231 or website for diagram

http://micro.magnet.fsu.edu/electromag/java/rutherford/

 

The protons are located in the nucleus.

 

9.  Chadwick/Curies (1932)

  Rutherford’s calculation of the proton mass (nuclear mass) fell short of the actual mass.  He suggested that there were other particles equal to the mass of the proton (p+) but with no charge.

…. This lead to the discovery of the NEUTRON.

 

10. Bohr Model  (Niels Bohr, Denmark 1913)

The atom did not collapse because the electron orbits the nucleus with a certain amount (quanta) of energy.   These are called shells or orbits.

Proof for this model is found in “Spectroscopy”.

 

11.  Quantum Mechanical Theory

- Electrons are both particles and waves.   Their location is described using probability equations and mathematical models.  The electrons occupy energy levels or shells rather than exact circular orbits.

 

 

 

 

 

 

 

 

 

 

10.  Pauli, Heisenberg

Q.1

Support – some experiments but put matter into categories like earth, fire, air, water

Contradict – no controlled experiments, didn’t accurately describe fire, many things could be broken down into simpler things, they thought water was an element

 

Q.2  They were driven by riches!  If they could do it, they would be famous and powerful.

 

Q.3  His experiments produced new pure chemicals with new properties that could lead to new applications.

 

 

Q.5  The law of multiple of proportions

 

Q.6

Compound 1   N / O = 0.3160 / 0.0903   = 3.499

Compound 2   N/O  =  0.3160/ 0.3611    = 0.875

 

           3.499/0.875 = 4        so the formula of compound two is NO4

 

Compound 3  N / O = 0.3160 / 0.7223    = 0.4375

           3.499/0.437 = 8       so the formula of compound three is NO8

 

Compound 4   N/O = 0.3160 / 0.5417     = 0.5833

 

           3.499/0.5833 =  6      ……………………………NO6

          

 

 

 

Homework pp223-228

p.228

Q.1-6

 

1.  To explain observations, communicate findings, help guide and predict future science experiments, seeing a physical model triggers understanding in new ways, simplifies complex things

 

2.  Invisible beam could be deflected or controlled by magnets as shown by the pattern on the florescent screen.

-Cathode Ray Tube (CRT)   -- Sir William Crookes (late 1800’s)

 

3. Beam originated at the negative electrode (cathode) and traveled to the positive electrode (anode ) leaving a shadow on the fluorescent screen.    (Heath p223 …see the cross shaped anode and the pink outline caused by the electrons ).

 

 

4/5.   Thomson – Cathode ray of a certain voltage  was deflected by a magnetic field.   Physicists can calculate the charge (C) – (coulomb= 6.25x1018  electrons)   to mass (g) ratio. 

 Found the e- was 1/2000 mass of a proton.

 

6. 

How was the proton discovered?

 

Excitation (electrically) of H2 gas produced a H atom without an electron…. which is a H nucleus = H+ = 1 proton.

It is 2000 x more massive than an electron and positively charged.

(p.225 shows the tube Thomson designed to detect protons)

 

 

 

Hebdon

Wksh.1 Q.7-12

Hmwk.

(Heath p.233 Q.1-5) on Thurs. in class

 

7.  The nucleus was only a fraction of the size of the atom.

( About the size of a PEA compared the whole of BC Place)

so Thomson’s model was incorrect because it had the Protons and Electrons occupying equal space.

 

8.  The neutron helps keep the protons in the nucleus from coming apart because they would like to repel each other. 

The neutron contributes to the ATOMIC MASS of the atom.

 

 

9.  All of the definite proportions, multiple proportions… conservation of mass rules still hold,

but Dalton thought the atom was “indivisible”…. is it?

NOooooooo…. it is divisible says JJ and Ruthy.

 

10.  Protons and Neutrons?

 

11.(see table “Maximum Penetrating…”  )

     a.   alpha can be stopped by paper

             beta and gamma go through

 

     b.  only gamma

 

12.      See :molar masses