1. Atoms, Molecules, and Ions
Chapter 2
Atoms, Molecules, and Ions

2. History Greeks Democritus and Leucippus - atomos Aristotle - elements.
Alchemy
Robert Boyle - experimental definition of element.
Lavoisier- Father of modern chemistry.
He wrote the book.

3. Laws Conservation of Mass
Law of Definite Proportion - compounds have a constant composition.
The react in specific ratios by mass.
Multiple Proportions- When two elements form more than one compound, the ratios of the masses of the second element that combine with one gram of the first can be reduced to small whole numbers.

4. Simple Ratios in Compounds
Water has 8 g of oxygen per g of hydrogen.
Hydrogen peroxide has 16 g of oxygen per g of hydrogen.
16/8 = 2/1
Small whole number ratios.
So the formula of Hydrogen Peroxide is H2O2

5. Proof
Mercury has two oxides. One is 96.2 % mercury by mass, the other is 92.6 % mercury by mass.
Show that these compounds follow the law of multiple proportion.
Speculate on the formula of the two oxides.

6. Dalton’s Atomic Theory
1. Elements are made up of atoms 2. Atoms of each element are identical. Atoms of different elements are different. (We need to address this one a bit further) 3. Compounds are formed when atoms combine. Each compound has a specific number and kinds of atom. 4. Chemical reactions are rearrangement of atoms. Atoms are not created or destroyed.

7. A Helpful Observation
Gay-Lussac - Under the same conditions of temperature and pressure, compounds always react in whole number ratios by volume.
Avogadro - interpreted that to mean at the same temperature and pressure, equal volumes of gas contain the same number of particles.
(called Avogadro’s Hypothesis)

8. Experiments to determine what an atom was
J. J. Thomson - used Cathode ray tubes to study the electrical charges found in atoms.

9. Thomson’s Experiment
Voltage source - +

10. Thomson’s Experiment
Voltage source - +

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

12. Thomson’s Experiment
Voltage source
By adding an electric field

13. Thomson’s Experiment Voltage source + -
By adding an electric field, he found that the moving pieces were negative, because they moved away from the negative charge.

14. Thomsom’s Model Found the electron.
Couldn’t find positive (for a while).
Said the atom was like plum pudding.
A bunch of positive stuff, with the electrons able to be removed.

15. Millikan’s Experiment
Atomizer
Oil droplets - +
Oil
Telescope

16. Millikan’s Experiment
X-rays
X-rays give some electrons a charge.

17. Millikan’s Experiment
Some drops would hover
From the mass of the drop and the charge on
the plates, he calculated the mass of an electron

18. Radioactivity Discovered by accident Bequerel Three types
alpha- helium nucleus (+2 charge, large mass)
beta- high speed electron
gamma- high energy light

19. Rutherford’s Experiment
Used uranium to produce alpha particles.
Aimed alpha particles at gold foil by drilling hole in lead block and inserting a small bit of alpha emitting particles.
Since the mass is evenly distributed in gold atoms alpha particles should go straight through.
Used gold foil because it could be made atoms thin.

20. Florescent
Screen
Lead block
Uranium
Gold Foil

21. What he expected

22. Notice that there is no deflection in the beam.

23. Because, he thought the mass was evenly distributed in the atom.

24. What he got was much different

25. 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.
Refer to the animations on the website for more detail.

26. The beam was often deflected+

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

28. Sub-atomic Particles
Z - atomic number = number of protons determines type of atom.
A - mass number = number of protons + neutrons. (Sometimes you will see N)
Number of protons = number of electrons if neutral.

29. Symbols A
Charge goes here X Z 23 +1 Na 11

30. Chemical Bonds The forces that hold atoms together.
Covalent bonding - sharing electrons.
Makes molecules.
Chemical formula - the number and type of atoms in a molecule.
C2H6 has 2 carbon atoms, 6 hydrogen atoms,
Structural formula shows the connections, but not necessarily the shape.

31. H H H C C H H H
There are also other model that attempt to show three dimensional shape.
This is called a Ball and stick model.

32. Ions Atoms or groups of atoms with a charge.
Cations - positive ions - get by losing electrons(s).
Anions - negative ions - get by gaining electron(s).
Ionic bonding - held together by the opposite charges.
Ionic solids are called salts, the most notable one being Sodium Chloride or Table Salt (NaCl).

33. Polyatomic Ions Groups of atoms that have a charge.
Yes, you have to memorize them.
Lists are on the website and on the given sheet.

34. Periodic Table

35. Metals
Conductors
Lose electrons
Malleable and ductile

36. Nonmetals
Brittle
Gain electrons
Covalent bonds

37. Semi-metals or Metalloids

38. Alkali Metals or Group I Metals

39. Alkaline Earth Metals or Group II Metals

40. Halogens or Group VII Metals

41. Transition metals

42. Noble Gases or Inert Gases or Group VIII

43. Inner Transition Metals or Rare Earth Metals

44. You can use the chart to help you with charges+1 +2 -3 -2 -1

45. Naming compounds
There are basically 2 types of compounds but we can combine the rules. Ionic and Covalent
We start by looking at the location of the first element in the compound on the periodic chart.
If it is to the left of the metalloid line, they we need to use prefixes. They are on another sheet.
If it is between the metalloid line up to the first two columns (IIA) then we need Roman Numerals. These are summarized on your Ion Sheet.
If it is in the first two columns on the right (IA and IIA), then we just write the ions as shown.

46. More nomenclature

47. Ionic Compounds - Practice
Have to know what ions they contain:
CaS K2S AlPO4
K2SO4 FeS CoBr3
Fe2(SO4)3 MgO MnO
KMnO4 NH4NO3 Hg2Cl2
Cr2O3 KClO4 NaClO3
AgNO3 Cr(ClO)6

48. Prefixes 1 – Mono - 2 – Di - 3 – Tri - 4 – Tetra - 5 – Penta -
6 – Hexa -
7 – Hepta -
8 – Octa -
9 – Nona -
10 – Deca -

49. Naming Covalent Compounds
Use the same rules as before !
CO2 CO
CCl4
N2O4
XeF6
N4O4
P2O10

50. Guidelines Charges must add up to zero.
This is true for every single compound.
Get charges from table, name of metal ion, or memorized from the list.
Use parenthesis to indicate multiple polyatomic ions. Example: Fe(NO3)2

51. A Few Examples Sodium Nitride Sodium - Na is always +1
nitride - ide tells you it comes from the table
nitride is N-3

52. Na+1 N-3 Ionic Formulas Sodium nitride Sodium: Na is always +1
Nitride: - ide tells you it comes from the table
and we know that nitride is N-3
Na+1
N-3
We see that one of each ion doesn’t total to zero.

53. Na3N Na+1 N-3 Ionic Formulas Doesn’t add up to zero
We need 3 Na+1 ions to make a total positive charge of +3 and it balances the -3 charge on the nitride ion.
Na+1
N-3
Na3N

54. Formula Writing Sodium sulfate Calcium iodide Lead (II) oxide
Lead (IV) oxide
Mercury (I) sulfide
Barium chromate
Aluminum hydrogen sulfate
Cerium (IV) nitrate

55. More Names and formulas

56. Acids Substances that produce H+1 ions when dissolved in water.
All acids begin with H.
Two types of acids:
Oxyacids (HNO3 : they contain oxygen)
Non-oxyacids ( HCl and H2S don’t have oxygen)
Refer to the website for more detail.

57. Naming acids If the formula has oxygen in it
write the name of the anion, but change
- ate to - ic acid
- ite to - ous acid
Watch out for sulfuric and sulfurous
H2CrO4  Chromic Acid
H2SO4  Sulfuric Acid
HNO2  Nitrous Acid

58. Naming acids If the acid doesn’t have oxygen Add the prefix hydro -
change the suffix - ide to - ic acid
HCl  Hydrochloric Acid
H2S  Hydrosulfuric Acid
HCN  Hydrocyanic Acid

59. Formulas for acids Hydrofluoric acid Dichromic acid Carbonic acid
Hydrophosphoric acid
Hypochlorous acid
Perchloric acid
Phosphorous acid

60. A Few Words About Hydrates
Some salts trap water crystals when they form crystals.
These are hydrates.
Both the name and the formula needs to indicate how many water molecules are trapped.
In the name we add the word hydrate with a prefix that tells us how many water molecules.
We will do a Fun Hydrate lab later in the year.

61. Hydrates
In the formula you put a dot and then write the number of molecules.
Calcium chloride dihydrate = CaCl2 · 2 H2O
Chromium (III) nitrate hexahydrate = Cr(NO3)3 · 6 H2O
SPECIAL NOTE: When determining the formula weight of a hydrate, remember that the raised dot is not a multiplication sign. It is a symbol showing the combination of the two.

62. An Example Let’s look at BaCl2 · 2 H2O The weight of Ba is 137.33 g.
The weight of Cl is g.
So the weight of BaCl2 is g
The weight of water is 18 g. so 2 are 36 grams.
The weight of the compound is:
g + 36 g = grams.