UNIT 2 – THE ATOM Lesson 2.1 Sept 19
1. The history of describing what things are made of, “ the early study of matter” was not called chemistry.
Democritus used the word “atom” to describe the smallest part of matter that was indivisible.
Early Models of the Atom
Greeks – philosophers, thinkers,”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. The philosopher’s stone.
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.
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.
8. Chadwick/Curies (1932)
9. Bohr Model
10. Pauli, Heisenberg
Elements and the Periodic Table – Atomic Structure
1. A good theory : explains observations, able to make predictions, helps in design of experiments,
2. NO…. the conflicts help revise the present theory
3. When compounds react Dalton would say the atoms in the molecules just rearrange.
4. Dalton
+ law of proportions and mass
- Couldn’t explain electrical atomic particles
5. Thomson
+ explained electrons and protons
- The e- and p+ were evenly distributed
6. Rutherford
+Nucleus contains most mass, positive
- Couldn’t figure out why it didn’t collapse
7. Bohr
+ electrons had energy in orbits that showed spectra
- Couldn’t account for complicated electron systems bigger than Hydrogen
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