1. Molecules and Compounds Compounds Display Constant Composition
Elements combine in fixed Proportions
Law of Constant Composition
H2O
CO2

2. Molecules and Compounds Compounds Display Constant Composition
If we decompose water, we find 16.0 grams of oxygen to every 2.00 grams of hydrogen. This produces an Oxygen to Hydrogen mass ratio of 8.0.
Mass ratio = grams = 8.0
2.00 grams
Water has a constant Mass Ratio of Oxygen to Hydrogen of 8.0.

3. Molecules and Compounds Chemical Formulas: How to Represent Compounds
Elements present
Relative numbers
Subscripts
Part of the definition
Changing subscript changes compound
Metals – Left-hand side of Periodic Table
Listed first
Nonmetals – Right-hand side of the Periodic Table
Those to the left-
More Metal-like

4. Significance of Chemical Formulas
A chemical formula indicates the relative number of atoms of each kind in a chemical compound.
For a molecular compound, the chemical formula reveals the number of atoms of each element contained in a single molecule of the compound.
example: octane — C8H18

5. Molecules and Compounds Writing Chemical Formulas
Compound containing 2 aluminum atoms to every 3 oxygen atoms
Al2O3
Compound containing 3 oxygen atoms to every 1 sulfur atom
SO3

6. Molecules and Compounds Chemical Formulas: How to Represent Compounds
Water – H2O
Hydrogen and oxygen atoms
2:1 ratio
Symbol and subscript
Dihydrogen monoxide

7. Chemical Formulas and Compounds Chemical Formulas: How to Represent Compounds
Carbon dioxide – CO2
Carbon and oxygen atoms
1:2 ratio
Symbol and subscript
Carbon dioxide
Two nonmetals
Left-most listed first
One carbon – not mono

8. The chemical formula for an ionic compound represents one formula unit—the simplest ratio of the compound’s positive ions (cations) and its negative ions (anions).
example: aluminum sulfate — Al2(SO4)3
Parentheses surround the polyatomic ion SO42- to identify it as a unit. The subscript 3 refers to the unit.

9. Molecules and Compounds Writing Chemical Formulas Polyatomic Ions
Contain several identical groupings of atoms
Polyatomic Ions
Parenthesis
Mg(NO3)2
Magnesium nitrate

10. Molecules and Compounds Writing Chemical Formulas Polyatomic Ions
Mg(NO3)2
1 Mg
2 N
6 O

11. Molecules and Compounds Molecular View of Elements and Compounds
Atomic Elements
Single atoms
Most Elements
Molecular Elements
Diatomic atoms
Two atoms bonded together
H2, N2, O2, F2, Cl2, Br2, I2
Molecular Compounds
Two or more Nonmetals
Ionic Compounds
Metal and nonmetal

12. Molecules and Compounds Molecular View of Elements and Compounds

13. Molecules and Compounds Writing Formulas for Ionic Compounds
Charge Neutral
Most elements form only one type of ion
Predictable charge
Sodium chloride
Na  +1
Cl  –1
NaCl
Magnesium chloride
Mg  +2
MgCl2

14. Common Monatomic Ions (pg.221 in your textbook)

15. Common Monatomic Ions…

16. Molecules and Compounds Writing Formulas for Ionic Compounds
Write the symbol for the metal and its charge
Write the symbol for the nonmetal and its charge
Charge (without sign) becomes subscript for other ion
Reduce subscripts to smallest whole number ratio
Check that the sum of the charges of the cation cancels the sum of the anions

17. Molecules and Compounds Writing Formulas for Ionic Compounds
Ionic compound between aluminum and oxygen
Al O2–
Al2O3
2 (+3) = +6
3 (–2) = –6

18. Molecules and Compounds Writing Formulas for Ionic Compounds
Ionic compound between magnesium and oxygen
Mg O2–
MgO
1 (+2) = +2
1 (–2) = –2
Smallest whole number ratio is 1:1

19. Molecules and Compounds Naming Ionic Compounds
Metal and Nonmetal
Two Types
Type I
Metal has constant predictable charge
Inferred from group number in Periodic Table
Type II
Charge NOT always the same
Transition Metals

20. Molecules and Compounds Naming Ionic Compounds Type I Binary Ionic Compounds
Binary compounds
Two different kinds of elements
Cation + anion with IDE
Metal
Predictable constant charge
Name of metal
Nonmetal
Name of nonmetal
Ending  IDE

21. Molecules and Compounds Naming Ionic Compounds Type I Binary Ionic Compounds
Binary compounds
Two different kinds of elements
Cation + anion with IDE
Metal
Predictable constant charge
Name of metal
Nonmetal
Name of nonmetal
Ending  IDE

22. Molecules and Compounds Naming Ionic Compounds Type I Binary Ionic Compounds
MgF2
Metal  Magnesium
Nonmetal  Fluoride
Magnesium fluoride
KBr
Metal  Potassium
Nonmetal  Bromine
Potassium bromide

23. Molecules and Compounds Naming Ionic Compounds Type I Binary Ionic Compounds
CaCl2
Metal  Calcium
Nonmetal  Chlorine
Calcium chloride
Na2O
Metal  Sodium
Nonmetal  Oxygen
Sodium oxide

24. Molecules and Compounds Naming Ionic Compounds Type II Binary Ionic Compounds
Binary compounds
Two different kinds of elements
Cation + anion with IDE
Metal
Charge NOT always the same
Transition metals and roman numeral for charge
Name of metal
Nonmetal
Name of nonmetal
Ending  IDE

25. Molecules and Compounds Naming Ionic Compounds Type II Binary Ionic Compounds
FeCl3
Metal  Iron
Nonmetal  Chlorine
Charge on Iron must be +3
Iron(III) chloride
CrO
Metal  Chromium
Nonmetal  Oxygen
Charge on Chromium must be +2
Chromium(II) oxide

26. Molecules and Compounds Naming Ionic Compounds Type II Binary Ionic Compounds
PbCl4
Metal  Lead
Nonmetal  Chlorine
Charge on Lead must be +4
Lead(IV) chloride
Must determine charge of Cation from the Formula

27. Molecules and Compounds Naming Ionic Compounds Polyatomic Ions
Group of atoms with an overall charge
Common Polyatomic Ions on pg. 226 in textbook. MEMORIZE (flashcards?)

30. Molecules and Compounds Naming Ionic Compounds Polyatomic Ions
KNO3
Metal  Potassium
Nonmetal  Nitrate
Potassium nitrate
FeSO4
Metal  Iron
Nonmetal  Sulfate
Iron(II) sulfate

31. Ionic Compounds Containing Polyatomic Ions….
Write the formula for tin(IV) sulfate
Sn(SO4)2

32. Molecules and Compounds Naming Molecular Compounds
Two or more nonmetals
Right of the Periodic Table
Binary Molecular Compounds
Two elements
Most “metal-like” first
Prefix [Element 1] Prefix [Element 2]
Do not begin with “mono” and if prefix is two syllables (& element starts with vowel) then drop the ending vowel of prefix.
Prefixes
Mono – 1
Di – 2
Tri – 3
Tetra – 4
Penta – 5
Hexa – 6
Hepta – 7
Octa – 8
Nona – 9
Deca - 10

33. Molecules and Compounds Nomenclature: Naming Compounds
Systematic ways to name compounds
Common names
Water
H2O
Common name  Water
Systematic name  Dihydrogen monoxide

34. Molecules and Compounds Naming Molecular Compounds
Most “metal-like” – Carbon
Nonmetal – Oxygen
Carbon dioxide
N2O
Most “metal-like” – Nitrogen
Dinitrogen monoxide

35. Give name for As2O5:
Write formula for oxygen difluoride:

36. Molecules and Compounds Naming Acids
Molecular Compounds
Form H+
Sour Taste
Binary Acids- acids that consist of two elements (usually hydrogen and a halogen)
Oxyacids – acids that contain hydrogen, oxygen and a third element (usually a nonmetal)

37. Binary Acids… If anion ends in “ide” then acid name is “hydro—ic”
HCl hydrochloric acid
HBr hydrobromic acid
HI hydroiodic acid

38. Naming Oxyacids No “hydro” in name
If anion ends in “ate” then acid name is “—ic”
If anion ends in “ite” then acid name is “—ous”

39. Oxyacids Anion Acid _____ sulfate SO42- sulfuric acid H2SO4
sulfite SO sufurous acid H2SO3 nitrate NO3- nitric acid HNO3
phosphate PO phosphoric acid H3PO4

40. Salts
An ionic compound composed of a cation and the anion from an acid is often referred to as a salt.
examples:
Table salt, NaCl, contains the anion from hydrochloric acid, HCl.
Calcium sulfate, CaSO4, is a salt containing the anion from sulfuric acid, H2SO4.

41. Oxidation Numbers
The charges on the ions in an ionic compound reflect the electron distribution of the compound.
In order to indicate the general distribution of electrons among the bonded atoms in a molecular compound or a polyatomic ion, oxidation numbers are assigned to the atoms composing the compound or ion.
Unlike ionic charges, oxidation numbers do not have an exact physical meaning: rather, they serve as useful “bookkeeping” devices to help keep track of electrons.

42. Assigning Oxidation Numbers
In general when assigning oxidation numbers, shared electrons are assumed to “belong” to the more electronegative atom in each bond.
More-specific rules are provided by the following guidelines.
The atoms in a pure element have an oxidation number of zero.
examples: all atoms in sodium, Na, oxygen, O2, phosphorus, P4, and sulfur, S8, have oxidation numbers of zero.

43. Assigning Oxidation Numbers, continued..
The more-electronegative element in a binary compound is assigned a negative number equal to the charge it would have as an anion. Likewise for the less-electronegative element.
Fluorine has an oxidation number of –1 in all of its compounds because it is the most electronegative element.

44. Assigning Oxidation Numbers, continued..
4. Oxygen usually has an oxidation number of –2.
Exceptions:
In peroxides, such as H2O2, oxygen’s oxidation number is –1.
In compounds with fluorine, such as OF2, oxygen’s oxidation number is +2.
5. Hydrogen has an oxidation number of +1 in all compounds containing elements that are more electronegative than it; it has an oxidation number of –1 with metals.

45. Assigning Oxidation Numbers, continued..
The algebraic sum of the oxidation numbers of all atoms in an neutral compound is equal to zero.
The algebraic sum of the oxidation numbers of all atoms in a polyatomic ion is equal to the charge of the ion.
Although rules 1 through 7 apply to covalently bonded atoms, oxidation numbers can also be applied to atoms in ionic compounds similarly.

46. Assigning Oxidation Numbers, continued..
Assign oxidation numbers to each atom in the following compounds or ions: a. UF6 b. H2SO4 c. ClO3-

47. Molecules and Compounds Nomenclature Summary

48. Molecules and Compounds Formula Mass & Molar Mass
Formula Mass - Average mass of the Molecules that compose a compound (in a.m.u.’s)
Molar Mass – Average mass of the molecules that compose a mole (6.02x1023) of the compound (in grams/mole)
Same values different units!

49. Molar Mass Calculation
What is the molar mass of barium nitrate, Ba(NO3)2?
g/mol