Download Chemical Formulas and Chemical Compounds

Chemical Formulas and Chemical Compounds
A correctly written chemical formula must represent the known facts about the analytically
determined composition of the compound
Used to represent amounts of substance
-H2O can represent: 1 mole of water molecules
1 molecule of water
1 molar mass of water molecules
Monatomic Ions: Ions formed from a single atom
-Followed by the name “ion”
-Cation combined with anion
Binary Compounds: Compounds composed of 2 different elements
-Drop ending of element name and add “ide”
Binary Ionic Compound: Compound composed of a metal and a non-metal
1. Write cation first
2. Subscripts represent number of atoms present
a. If no subscript: One is understood
b. Charges are not included in chemical
1. Compound is neutral
c. Charges can be crossed over to get
d. Find number of ions needed to equalize + and – charges
Steps
1. Write symbols for ions side by side, positive ion first
2. Cross over charge values to give subscripts
3. Check subscripts and write formula
Na + Cl
Mg + Br
Al + O
Li2O
formulas
subscripts
CaCl2
Different names are needed for positive ions of 2 different charges formed by the same metal (dblock)
2 Different naming systems
1. Old: Ion with lower charge - ous
Ion with higher charge – ic
Ex: Cu+
Cu2+
2. New: Charge is indicated by Roman numeral
(Stock system)
Ex: Cu+
Cu+2
Nomenclature: Term that refers to methods of naming chemical compound
Compounds Containing Polyatomic Ions
-All but ammonium are – charged
-Oxyanions: Polyatomic ions that contain O2
-In several cases 2 different oxyanions are formed from the same 2 elements
-NO2and
NO3(ite: less oxygen)
(ate: more oxygen)
-Ex:
-EX: Sodium Carbonate
-Ex: Aluminum Sulfate
-Ex: Ammonium sulfate
CaSO4
NaNO3
Ba
-Ex: Copper (II) nitrate
Fe(NO3)2
Cu2SO4
Binary Molecular Compounds
-Compounds between nonmetals: Molecular
-Old System (Greek prefixes)
-Least electronegative element is given 1st
-Oxygen and halogens are 2nd
-Prefix Rules
1. Used with name of 1st element
a. Only if more than one atom of that element is present
2. Second element
a. Prefix if more than 1 compound can be formed by the 2 elements
b. The root of the name of the second element
c. Ending: “ide” (indicates compound containing 2 elements)
EX:
N2O5
P8Cl7
S3F9
Petacarbon hexachloride
Tetranitrogen octaphosphide
Trifluoride hexaiodide
Acids: Molecular compound that contains one or more H
Binary acid: H and a halogen (a more electronegative non-metal)
-Occurs in a water solution
-Ex: HCl
Oxyacid: Acids containing H, O, and a 3rd element
-Many polyatomic ions are produced by loss of H ions from oxyacids
Ex: Sulfuric acid
Phosphoric acid
Nitric acid
Salt: Ionic compound composed of cation and anion of an acid
Ex: CaSO4
Hydrates: Compounds that attract and hold water molecules in their crystal structure
Water of Hydration: Water locked in compound, can be removed by heating
Anhydrous: Solid residue remaining after water has been removed
Formula of hydrated compound: Place raised dot after anhydrous formula followed by the
number of water molecules per formula unit of compound
Ex: Copper II sulfate pentahydrate (hydrate: water)
Sodium carbonate hepta hydrate
Oxidation Numbers or oxidation states: Assigned to atoms in molecules, including molecular
ions, to show general distribution of electrons among bonded atoms
-Ownership is given to the more electronegative atom in bond
Rules for assigning oxidation Numbers
1. Uncombined elements: 0
2. Monatomic ion = to charge
3. Fluorine = -1
4. Oxygen = -2
-Except in: Peroxides H2O2: O = -1
Superoxides KO2: O = -1/2
Compounds with Fluorine O = +2
+
5. H = 1
-Except in compounds with metals (NaH) –1
6. The more electronegative element in a binary compound
-Oxidation # = to charge of ion
7. Algebraic sum of oxidation #s in neutral compound = 0
8. Algebraic sum of oxidation #s in polyatomic ions = the charge
Practice: Assign the oxidation # for the purple element
1. CF4 ____
2. PCl3 _____
3. SO2 ______
4. HNO3 _____
5. SiO2 _______
6. KH ________
7. P2O5 _______
8. HClO2 _______
9. PCl3 _______
10. PCl5 _______
11. POCl3 _______
12. SO3 2-_________
Empirical Formula: Simplest ratio of atoms in a compound
Ex: B2H6 : Empirical Formula BH3
Steps:
1. Convert each amount to moles
2. Divide each mole amount by the smallest mole amount
a. Results in your subscripts
b. Must be close to a whole number; if not multiply by 2
3. Percents can be interchanged for grams
Ex: If you have 2.128 g Cl and 1.203 g Ca what is the empirical formula?
If you have 3.50% Fe and 1.50% O what is the empirical formula?
Molecular Formula: Gives the actual # of atoms of each element in a molecular compound
(empirical formula)X = molecular formula
-X is the integral factor
-Multiply subscripts in empirical formula by the integral factor
X = Molecular formula mass/empirical formula mass
Ex: If the molecular formula mass is 283.889g and the empirical formula is P2O5 what is the
molecular formula?