1. Chemical Formulas and Chemical Compounds
Chapter 7
Chemical Formulas and Chemical Compounds

2. Sect. 7-1: Chemical Names and Formulas
Chemical formulas indicate what elements/ions are in the compound and in what ratio

3. Polyatomic ions get ion name ( pg. 210)
Naming monatomic ions
Cations get the element name
Anions get the root of the element name with –ide ending
Polyatomic ions get ion name ( pg. 210)

4. Binary Ionic Compounds – Steps for formula writing
1. Write down the symbols for the ions, cation listed first
2. Identify charges and “criss-cross” as needed
3. Re-write formula without showing charges

5. Naming binary ionic compounds
Name cation
Name anion (remember –ide ending)
If cation is multi-valent (can have more than one charge), add roman numeral in parenthesis following cation name to indicate charge
Stock system of nomenclature

6. Compounds containing polyatomic Ions
Oxyanions – polyatomic ions containing oxygen
Many are made of same 2 elements, so more common ion gets –ate ending and the one with less oxygen gets –ite ending
If more than 2 oxyanions, hypo- is added for less then the –ite and per- is added for more than –ate
Naming of compounds is same as binary

7. When more than one polyatomic ion is needed to balance the charges in a formula, parenthesis are required around the polyatomic ion

8. Naming Binary Molecular Compounds
“Old” system of naming
Prefixes are used to tell how many of each element are present in the molecular formula
Less electronegative element is listed first and is only given a prefix if there is more than one
2nd element is given a prefix, then the root of the element name, and then –ide ending
“o” or “a” at end of prefix is dropped when element name starts with a vowel

9. Numerical Prefixes 1 mono- 6 hexa- 2 di- 7 hepta- 3 tri- 8 octa-
4 tetra- 9 nona-
5 penta deca-

10. Rules for naming acids

11. Naming Acids
Binary Acids (contains hydrogen and one other element)
Use prefix hydro- to name the hydrogen part of the compound
The rest of the name consists of a form of the root of the element plus the suffix –ic and then the word acid

12. Naming Oxyacids Oxyacid- acid that contains hydrogen and an oxyanion
First determine anion present
If anion ends with –ate, replace with suffix –ic
Ex: HNO3; NO3-1 is nitrate
Name is Nitric Acid

13. If anion ends with –ite, replace with suffix –ous
Ex: HNO2; NO2 is nitrite
Name is Nitrous Acid

14. Sect. 7-3: Using Chemical Formulas
Formula Mass – sum of the average atomic mass of all atoms in a formula unit, molecule, or ion
Units are amu (atomic mass units)

15. Molar mass for a compound is calculated by summing the masses of all elements present in one mole of the compound
Molar mass is numerically equal to formula mass, but units are g/mol
Ex: Calculate the molar mass of water

16. Molar mass can be used as a conversion factor to convert between moles and grams (use t-chart method)
1mol = molar mass in grams

17. Percent by mass of a compound =
Mass of element in sample of compound x 100
Mass of sample of compound
Can also be calculated by
Mass of element in 1 mol of compound x 100
Molar mass of compound

18. Percent composition – the percent by mass of each element in a compound

19. Sect. 7-4: Determining Chemical Formulas
Empirical formula – shows the smallest whole number ratio of elements in a compound (may or may not be same as molecular formula)

20. Steps for determining Empirical Formula
Determine percent composition (if not already given)
Assume 100 g sample and change % to units of grams
Convert grams of each element to moles
Divide all answers from step #3 by the smallest answer to obtain a whole number ratio

21. If step #4 does not give very close to whole numbers, multiply all answers by the same number to obtain whole numbers
Example 2.5 would be multiplied by 2 to get 5 or 2.3 would be multiplied by 3 to obtain 7

22. Calculation of a Molecular Formula
X (empirical formula) = molecular formula
X = molar mass of molecular formula
molar mass of empirical formula
X must be a whole number