1. Chapter 2A Chemical Formulas

3. Chemical Symbols Also called Chemical Formula Universal shorthand
Each element has its unique symbol
Symbol based on name:
English
Latin
When elements are uncombined, most are written as monatomic elements
No subscripts! H2
No little 2
7 are Diatomic Molecules

4. Diatomic Molecules
2 identical elements combined in a covalent bond together
NEVER found by themselves in nature
They are SO reactive that they are in a compound or a diatomic molecule
7 Elements in the shape of a SEVEN
MUST always be written diatomically when written by themselves
H2, N2, O2, F2, Cl2, Br2, I2
That means that it is the chemical symbol followed by a subscript 2

5. Chemical Formulas
Use a combination of chemical symbols and numbers to show both quantitative and qualitative information
Quantitative = Names the elements (symbols)
Qualitative = Number of atoms of each element (subscript)
Compounds are composed of combinations of elements CHEMICALLY COMBINED in definite proportions by weight.
H2O means for every ONE oxygen there are TWO hydrogen

6. Examples: Which elements are there and how many of each?
NaCl
H2O
H2SO4
N2O4
P4O10

7. Types of Formulas There are 3 types of formulas: 1. Molecular Formula
Empirical
Structural (We will talk about this one in a later chapter)
1. Molecular Formula
Tells you the actual number of atoms of an element in a compound
H2O2
2. Empirical Formula
Smallest whole-number-ratio of atoms or ions in a compound HO
3. Structural Formula
Indicates how the atoms are bonded to each other
We will learn how to draw these in a later chapter

8. Examples: Change these molecular formulas into empirical formulas
H2O2
C3H6
C6H12O6
P4O10
N2O4

9. Atoms vs. Ions: Review Atoms Ions
Electrically neutral (o) because it has EQUAL numbers of protons (+) and electrons (-)
Ions
Not neutral: either positively or negatively charged
If it loses electrons, it will have a (+ / -) charge and be (larger/smaller).
If it gains electrons, it will have a (+ / -) charge and be (larger/smaller).
Do you ever gain protons?

10. Polyatomic Ions Table E
Group of atoms covalently bonded together, possessing a charge
These ions ALWAYS stay as one unit and CANNOT be broken up
So, if there is a polyatomic ion in a compound, it will stay as a polyatomic ion and should be treated as ONE entity
When in a compound, there will be parentheses around the ion, unless there is only one ion
(NH4)3PO4
To find the total number of each element, you would distribute the subscript (like you would in math)
N = 1 x 3 = 3 Nitrogens
H = 4 x 3 = 12 Hydrogens
P = 1 Phosphorus
O = 4 Oxygens

11. Examples: Identify the Polyatomic ion. How many of each element?
KClO3
H2O2
H2SO4
KCr2O7
Pb3(PO4) 2
Al(OH) 3
(H3O) 2S
B2(S2O3) 3

12. Coefficients The number in FRONT of a formula
The number of units of the formula that are present
Multiply the ENTIRE formula by that number to find the total number of each atom present
2NaCl
There are 2 salt molecules or 2 Sodium and 2 Chlorine

13. Subscripts vs. Coefficients
Written to the lower right of a chemical symbol
Written smaller than chemical symbol
Only applies to single atoms or to polyatomic ions
Written to the left of the chemical symbol
Written the same size as the chemical symbol
Applies to every atom in molecule, including subscripts

14. Examples: How many of each element are there?
2Li2CO3
3MgCO3
4Ca3(PO4)2
5H2O

15. Hydrates When the crystal lattice of a solute binds with water
BaCl2 * 2H2O
FePO4 * 4H2O
The water does NOT react!
But, it does add mass to the compound
Think about shipping concentrated orange juice vs. whole orange juice
Anhydrate (anhydrous) is what it is called after it is heated and the water is removed (evaporated)

16. Open your book to p. 30 (1-15) 2 3 4 1 4 2 3 1

17. Writing Formulas All compounds must be electrically neutral.
That means that it CANNOT have a charge.
This is achieved by having a balance of positive and negative charges
Based on Oxidation States
Look at the periodic table p. 9 in your RT
For Example:
Na has an oxidation state of +1
Cl has an oxidation state of -1
If you put one of each of them together, the charges will cancel and the compound will be neutral.
NaCl has a 1:1 ratio
Positive ion (called a cation) is written first…this is usually a metal
Negative ion (called an anion) is written second…this is usually a nonmetal
For elements that do not have the same oxidation states, you have to do the “criss- cross method” to balance the charges

18. Criss-Cross Method Find the oxidation states of the elements
Elements that have more than one oxidation state will have a roman numeral that corresponds to the oxidation state you should use.
Iron (II) = +2 Iron (III) = +3
Lead (II) = +2 Lead (IV) = +4
If there is a polyatomic ion, it stays together and doesn’t change.
You may have to put parentheses around it.
Just look at the charge on the ion and use it in place of the oxidation state.
Then write the oxidation state of one as the subscript of the other
You just criss-cross them!
Kris Kross

19. Example: Write the following formulas using the criss-cross method.
Al+3 and F -
Ca+2 and N-3
K+ and Cl-
Mg +2 and I-
Li+1 and OH-1
NH4+ and SO4-2
Cu+2 and PO4-3

20. Naming Compounds There are 2 types of compounds: Ionic Compounds
Covalent Compounds
Often made up of a metal and a nonmetal
Electronegative difference is 1.7 or greater
Often made up of only nonmetals
Electronegative difference is less than 1.7

21. Ionic Compounds Binary Compounds Polyatomic Ions Stock System
Containing only TWO elements
Positively charged (usually metal) then negatively charged (usually nonmetal) particles
Names of the elements
End of second element is changed to -ide
Polyatomic Ions
If the polyatomic ion is negatively charged, just write both names
If the polyatomic ion is positively charged, change the nonmetal to –ide just as before
Stock System
If a metal has more than one oxidation state, write a roman numeral after the name to show which oxidation state to use.

22. Examples: Name the following compounds.
LiF
CaBr2
K2S
FeS
MgO
MnO
CoI3
Mg(OH)2
Al(ClO3)3
(NH4)2O2

23. Covalent Compounds Remember, generally, they contain 2 nonmetals
Molecular substance, not made up of ions
So, look at electronegativity values
Lower value goes first
The name of the second element will still be changed to –ide
Finally, you use a prefix to tell the reader how many of each element
If there is only ONE of the first element, no need to use mono-

24. Examples: Name the following compounds.
OF2
SF2
B2O3

25. Open your book to p (16-34)

26. STUDY!!!!!