1. Chemical Formulas and Chemical Compounds
Chapter 7

2. Chemical Names and Formulas
Section 7-1

3. Definitions
Chemical formula - Indicates the relative number of atoms of each kind in a chemical compound Molecular compound -The chemical formula reveals the number of atoms of each element contained in a single molecule of the compound Ionic compound - Consists of a lattice of positive and negative ions held together by mutual attraction

4. The chemical formula for an ionic compound represents one formula unit, the simplest ratio of the compounds positive ions (cations) and its negative ions (anions)

5. Monatomic Ions
By gaining or losing electrons many main- group elements form ions with noble-gas configurations
Ions are formed from a single atom
Rather than gain or lose electrons, atoms of carbon and silicon form covalent bonds in which they share electrons with other atoms
Elements from the d-block form +2, +3 ions, and in a few cases +1, +4 ions

6. Monatomic cations Identified simply by the element’s name
K+ Potassium cation
Mg2+ Magnesium cation

7. Monatomic anions The ending of the element’s name is dropped
Then the ending –ide is added to the root name
F Fluorine F-1 Fluoride anion
N Nitrogen N-1 Nitride anion

8. Binary Ionic Compounds
The total numbers of positive and negative charges must be equal.
Compounds are composed of two elements
The positive cation is always named/written first. For simple ionic compounds, use the same naming scheme as for monatomic cations and anions

9. Steps for determining a Binary Ionic Compound
Write the symbols for the ions side by side.
Write the cation first
Cross over the charges by using the absolute value of each ion’s charge as the subscript for the other ion
Check the subscripts and divide them by their largest common factor to give the smallest possible whole- number ratio of ions
Write the formula

10. The Stock System of Nomenclature
Nomenclature – naming system When an element forms two or more cations with different charges, use a Roman numeral to indicate an ion’s charge. Fe+2 iron(II) Fe+3 iron (III) Note: There is no element that commonly forms more than one monatomic anion

13. Naming According to the Stock System
Write the name of the cation
Indicate the charge with Roman numeral in parenthesis
Write the name of the anion

14. Oxyanions Oxyanions are polyatomic ions that contain oxygen
Some can combine to form more than one type

15. Naming Oxyanions
The name of the ion with the greater number of oxygen atom ends in – ate
The name of the ion with one less oxygen atom ends in –ite
The anion that has one less oxygen atom than
the –ite anion has the prefix hypo-
The anion that has one more oxygen atom than the –ate anion has the prefix per-

16. Examples of Oxyanions ClO- hypochlorite ClO2- chlorite ClO3- chlorate
ClO4- perchlorate

17. Naming Binary Molecular Compounds Use prefixes to represent how many atoms needed.
# of atoms needed
Prefix of Atom
mono- di- tri- tetra- penta- hexa- hepta- octa- nona- deca-

18. Rules for prefix system of nomenclature of binary molecular compounds
The element that has the smaller group number is usually written first.
If both elements are in the same group, the element whose period number is greater is written first.
The element is given a prefix only if it has more than one atom in the molecule.
The second element is named by combining a prefix indicating the number of atoms contributed by the element

19. Rules for prefix system of nomenclature of binary molecular compounds
Give the root of the name of the element and end in –ide (see note below)
The ‘o’ or ‘a’ at the end of a prefix is usually dropped when the word following the prefix begins with another vowel.
For example, monoxide instead of mono-oxide pentoxide instead of penta-oxide
The –ide indicates that the compound contains 2 elements or is binary

20. Naming Acids
Binary Acids - Acids that only have 2 elements, hydrogen and one other.
They are always prefixed with hydro- plus the anion ending in -ic.
Hydrochloric, hydrofluoric etc.
The hydro prefix is a dead giveaway that it is a binary acid.
KH is not an acid.

21. Ternary Acids
Ternary acids are acids with three elements, usually H, O and another nonmetal. Due to the presence of the oxygen, they are called oxyacids and the oxygen ion that bonds to the hydrogen is an oxyanion Acids are water solutions containing the acid compound.

22. Naming Ternary Acids
The oxyanion that ends in -ate changes the ending to –ic acid
The oxyanion the ends in –ite changes the ending to –ous acid.

23. H2SO4 H2CO3 HNO2 HClO3 HClO Sulfuric acid Carbonic acid Nitrous acid
Acid Formula
Acid Name
H2SO4
H2CO3
HNO2
HClO3
HClO
Sulfuric acid
Carbonic acid
Nitrous acid
Chloric acid
Hypochlorous acid

24. Instructions for:
Writing formulas for Ionic Compounds with Polyatomic ions Same as Writing formulas for Ionic Compounds but use table 2 on p 226 for the polyatomic ions!

25. Oxidation Numbers
Section 2

26. Assigning Oxidation Numbers
1. Atoms of pure elements have oxidation number zero.
2. In a binary compound, the more electronegative element is assigned the negative charge it would have as an anion.
3. Fluorine is always -1 since it is the most electronegative number.
4. Oxygen is usually -2 except for OF2 where it is +2 and H2O2 where it is -1.

27. 5. Hydrogen is +1 in all compounds that have a higher electro negativity.
Hydrogen is -1 when with a metal.
6. The sum of all oxidation numbers in a compound is zero.
7. The sum of all oxidation numbers in polyatomic ions is the charge of the ion.
8. Rule 7 applies to covalent and ionic compounds.

28. H2SO4 UF6 ClO3-1 HNO3 P4O10 N2O5 KH S = +6 U = +6 Cl = +7 N = +5
Oxidation Numbers
Examples
H2SO4
UF6
ClO3-1
HNO3
P4O10
N2O5 KH
S = +6
U = +6
Cl = +7
N = +5
P = +5
H = -1

29. Using Chemical Formulas
Section 7.3

30. Definitions
Formula mass - the sum of the average atomic masses of all atoms represented in its formula of any molecule, formula unit, or ion
Molar mass - the mass in grams of 1 mol of a substance
(The molar mass is numerically equal to its formula mass only in grams instead of an amu.)
Percentage composition - The percentage by mass of each element in a compound

31. Calculate Percent Composition
Percent composition of Cu2S.
2 mol Cu x g Cu = g Cu
1 mol Cu
1 mol S x g S = g S
1 mol S

32. Percent Composition of Cu2S
Molar Mass of Cu2S Cu 2 x = g S 1 x = g g % Cu = g Cu x 100 = % g Cu2S % S = g S x 100 = % S

33. Converting between Moles, Grams, and Particles
÷ molar mass
No. of atoms
Mass of element
No. of Moles
X x 1023
X molar mass
÷ 6.02 x1023

34. Mass of Com-pound No. of mole-cules No. of moles ÷ molar mass
X x 1023
Mass of Com-pound
No. of moles
No. of mole-cules
÷ 6.02 x 1023
X molar mass

35. Determining Chemical Formulas
Section 7.4

36. Empirical formula
Consists of the symbols for the elements combined in a compound with subscripts showing the smallest whole-number mole ratio of the different atoms in the compound
Ionic compound, the formula unit is usually the compound’s empirical formula.
Molecular compound the empirical formula does not necessarily indicate the actual numbers of atoms present in each molecule