1. The Evolution of Atomic Theory
Chapter 3

2. Law of conservation of Matter
When a chemical reaction takes place, matter is neither created nor destroyed

3. Law of Constant Composition
Multiple Samples of any pure chemical compound always contain the same percent by mass of each element making up the compound
Example: if a 50 g sample of pure water is decomposed into it’s component elements, you will obtain 5.6 g of hydrogen and 44.4 g oxygen gas
The percent by mass of these elements is therefore:

4. Dalton’s Atomic Theory
All matter is made of tiny indivisible particles called atoms.
2 Atoms can neither be created nor destroyed (they persist unchanged for all eternity)
3 Atoms of the same element are identical (in size, mass, and properties), those of different atoms are different.

5. Dalton’s Atomic Theory
4 A chemical reaction involves either the union or the separation of individual atoms.

6. Law of Multiple Proportions
A law proposed by Dalton which states that when elements combine, they do so in the ratio of small whole numbers.  For example carbon and oxygen react to form CO or CO2, but not CO1.8.   

7. Parts of an Atom J. J. Thomson - English physicist. 1897
Made a piece of equipment called a cathode ray tube.
It is a vacuum tube - all the air has been pumped out.

8. Thomson’s Experiment
Voltage source + -
Vacuum tube
Metal Disks

9. Thomson’s Experiment
Voltage source - +

10. + - Thomson Experiment Voltage source
Passing an electric current makes a beam appear to move from the negative to the positive end

11. Thomson’s Experiment
Voltage source + -
By adding an electric field

12. + - Thomson’s Experiment Voltage source
By adding an electric field he found that the moving pieces were negative

13. What Did Thomson Demonstrate?
Cathode rays:
Travel in straight lines
Are negatively charged
Are deflected by electric and magnetic fields

14. Thomson’s Model Found the electron Said the atom was like plum pudding
A bunch of positive stuff, with the electrons able to be removed

15. Rutherford’s Experiment
Ernest Rutherford English physicist. (1910)
Believed in the plum pudding model of the atom.
Used uranium to produce alpha particles.

16. Rutherford’s Experiment
Florescent
Screen
Uranium
Lead block
Gold Foil

17. What he expected

18. Why ??
The alpha particles to pass through without changing direction very much
The positive charges were spread out evenly. Alone they were not enough to stop the alpha particles

19. What he got

20. How He Explained It Atom is mostly empty
Small dense, positive piece at center
Alpha particles are deflected by it if they get close enough

21. How He Explained It +

22. Density and the Atom
Since most of the particles went through, it was mostly empty.
Because the pieces turned so much, the positive pieces were heavy.
Small volume, big mass, big density
This small dense positive area is the nucleus

23. Modern View The atom is mostly empty space Two regions
Nucleus- protons and neutrons
Electron cloud- region where you might find an electron

24. Structure of Atom There are two regions:
The nucleus: with protons and neutrons
Almost all the mass
Electron cloud- Most of the volume of an atom
The region where the electron can be found

25. Subatomic Particles
Name
Symbol
Charge
Electron e- -1
Proton p+ +1 n0

26. Size of Atom Nucleus tiny compared to atom
IF the atom was the size of a stadium, the nucleus would be the size of a marble.
Radius of the nucleus near 10-15m.
Density near 1014 g/cm

27. X H H (D) H (T) U Atomic number (Z) = number of protons in nucleus
Mass number (A) = number of protons + number of neutrons
= atomic number (Z) + number of neutrons
Isotopes are atoms of the same element (X) with different numbers of neutrons in their nuclei
Mass Number X A Z
Element Symbol
Atomic Number H 1
H (D) 2
H (T) 3 U
235 92
238

28. Isotopes Dalton was wrong.
Atoms of the same element can have different numbers of neutrons
different mass numbers
called isotopes

29. The Periodic Table

30. The Periodic Table Each column is called a group.
Each row is called a period.

31. Alkali Earth Metal
Noble Gas
Halogen
Alkali Metal
Period
Group
2.4

32. Non-metals Not conductors of heat or electricity
Brittle cannot be rolled into wires or pounded into sheets.
Exist in two of the three states of matter at room temperature:
Gases- Oxygen
Solids- Carbon
No metallic luster and do not reflect light
You are to know the names (correct spelling) and symbols for these elements.

33. Metalloids Properties of both metals and non-metals
Silicon and Germanium are semi-conductors.

34. Alkali Metals IA Li Na K Rb Cs Fr

35. Alkali Metals
Very react-active metals that do not occur freely in nature.
They are Malleable, ductile and good conductors of heat an electricity
Softer than most other metal
Explode if they are exposed to water
Color flames
Li-red Na- Yellow K- lilac Rb- red Cs-blue

36. Alkaline Earth Metals Be Mg Ca Sr Ba Ra

37. Alkaline Earth Metals
Very reactive but not as reactive as the alkali metals
All are found in the earth’s crust but not in elemental form. Instead they are widely distributed in rock structures

38. Halogens F Cl Br I At

39. Halogens
Halogen means “salt-former” therefore compounds containing halogens are called “salts.”
All halogens exist as diatomic molecules, X2
The halogens exist, at room temperature, in all three states of matter
Solid-Iodine, Astatine
Liquid- Bromine
Gas- Fluorine, Chlorine
The halogens are too reactive to occur free in nature.

40. Transition metals Sc Ti V Cr Mn Fe Co Ni Cu Zn Y Zr Nb Mo Tc Ru Rh PdAg Cd La Hf Ta W Re Os Ir Pt Au Hg Ac

41. Transition Metals Ductile Malleable Conductors of heat and electricity
Iron, Cobalt and Nickel are they only elements known to produce a magnetic field

42. Noble Gases He Ne Ar Kr Xe Rn

43. Noble Gases Very un-reactive Very small quantities in the atmosphere
Monatomic
Low boiling points
He, Ne, and Ar form no known compounds

44. Rare Earth Metals

45. Rare Earth Metals Lanthanide Series High Luster
Conductors of electricity
Tarnish rapidly in air
Many ignite and burn
vigorously at elevated
temperatures
Actinide Series
All isotopes of all actinides
are radioactive
Actinides are very dense
Typically react with:
air (tarnishing)
boiling water or dilute acid
most non-metals in direct combination

46. Atomic Mass How heavy is an atom of oxygen?
There are different kinds of oxygen atoms.
More concerned with average atomic mass.
Based on abundance of each element in nature.
Don’t use grams because the numbers would be too small

47. Measuring Atomic Mass Unit is the Atomic Mass Unit (amu)
Each isotope has its own atomic mass we need the average from percent abundance.

48. Calculating averages
You have five rocks, four with a mass of 50 g, and one with a mass of 60 g. What is the average mass of the rocks?
Total mass = x x 60 = 260 g
Average mass = 4 x x 60 = 260 g

49. Calculating averages Average mass = 4 x 50 + 1 x 60 = 260 g 5 5 5
80% of the rocks were 50 grams
20% of the rocks were 60 grams
Average = % as decimal x mass % as decimal x mass % as decimal x mass +

50. Atomic Mass
Calculate the atomic mass of copper if copper has two isotopes. 69.1% has a mass of amu and the rest has a mass of amu.

51. Atomic Mass
Magnesium has three isotopes % magnesium 24 with a mass of amu, 10.00% magnesium 25 with a mass of amu, and the rest magnesium 25 with a mass of amu. What is the atomic mass of magnesium?
If not told otherwise, the mass of the isotope is the mass number in amu