Stoichiometry Unit Notes
Part I.
I. Formulas
A. Symbols: refer to your Periodic Table for element symbols, and Table S for names, if
necessary; use capitol letter with lower case letter next to it, if second letter needed!
B. Formulas
1) Quantitative vs. Qualitative
2) Empirical vs. Molecular
3) Coefficients vs. Subscripts
4) Polyatomic ions [Table E]
5) Hydrates
C. Writing Formulas
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Ionic compounds = metals + nonmetals; (+) and (-) ions bonded to form a neutral
compound
Write the name of the metal first, then the nonmetal name with the suffix “-ide”
Ionic compound = those made with positive and negative ions; contains a metal and
nonmetal, usually; has positive and negative charges that balance; have given or taken
electrons to form charges; generic name of “salt” is for any inorganic solid
Cations = positive ions; metals; give away electrons; less electronegative
Anions = negative ions; nonmetals; take electrons; more electronegative
II. Naming Compounds
Chemical compound = element symbols and their ratios that make up a chemical formula;
ratios of positive and negative charges given via subscripts
Two basic types:
1) Ionic Compounds: Neutral compounds made from (+) and (-) ions
2) Molecular compound = those made with only nonmetals; no actual charges involved due to
electrons being shared to form bond
A. Ionic Naming Rules
1) Binary Compounds: those containing ratios of just two elements bonded
1) Name metal [listed first]
2) Name nonmetal and change ending to “-ide”.
3) If metal ion has multiple charges [check PT!!], then list the charge of the metal
in this particular compound with a Roman numeral after the metal’s name.
Examples:]
2) Using Polyatomic Ions
Binary compounds = those that are made of only 2 elements
Polyatomic Ions = more than one atom bonded together having an overall charge
If more than one element is listed as a positive or negative portion of the compound, a
polyatomic ion is involved.
Use Table E in the Reference Tables to find and name polyatomic ions. Names and
charges are listed there.
Examples:]
3) Transition Metals: name the compound as listed above for ionic substances
 Calculate the charge of the transition metal using the formula below, or other
method
 Write the Roman Numeral of the charge in parenthesis after the metal’s name
Calculating the charge for a metal ion with multiple charges:
 Use the formula given below to help calculate the charge of the metal ion, then list the is charge
after the name of the metal using Roman numerals.
 Charge of the metal is the value for x. Use this number for the Roman numeral.
Aw+x Et-y
Where,
w(+x) + t(-y) = 0
A = metal ion,
w = number of metal atoms in formula
metal’s charge.
+x = charge of the metal
E = nonmetal ion
equal zero
t = number of nonmetal atoms in formula
-y = charge of the nonmetal
*Solve for “x” to find the
NOTE: All [+] and [-] charges
in a compound!!
Examples:
_______________________________________________________________________________________
NOTE: two methods needed to solve for charges or ratios of ions in a formula!
1) Solving for ratios when ions with charges given {ionic only!}
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Treat charges of the ions as FRACTIONS that need to be added;
Find the common denominator, and multiply out to adjust numerators
Numerators of the new fractions are the RATIOS of ions needed to make the compound!
2) When finding charges of metal ions in a completed formula
Use algebra equation: w(+x) + t(-y) = 0
Where: w = subscript of metal ion,
t = subscript of nonmetal ion
+x = charge of metal ion [solve for this!]
-y = charge of nonmetal ion
D. Molecular Naming
Compounds made from all nonmetals are named using another set of rules.
Names are created to describe the ratios of atoms present, rather than using charges
Rules:
1) Name the first element.
2) Provide prefix if more than one element is listed.
3) Name the second element, and change the ending to “-ide”.
4) Provide a prefix to describe how many are present [for 1-10 atoms].
Prefixes:
1 = mono2 = di3 = tri4 = tetra5 = pentaExamples:]
6 = hexa7 = hepta8 = octa9 = nona10 = deca-
III. Chemical Reactions and Equations
A. Chemical vs. Physical Changes
a. Chemical changes = those that create new products from the starting materials; not
reversible!
b. Physical changes = those made to the phase of the substance; reversible!
B. Reactants vs. Products:
a. Reactants = substances that are to the left of the arrow in a chemical equation;
starting materials
b. Products = substances to the right of the arrow in a chemical equation; what is
produced by the reaction
C. Endothermic vs. Exothermic:
ENdo- = heat Enters! Heat is a Reactant!
EXo- = heat Exits! Heat is a Product!
D. Conservation Laws
Law of Conservation of Matter and Energy = no matter or energy is created/destroyed
during an ordinary chemical reaction
E. Balancing Equations
Chemical equation = formulas of the reactants and products in molar ratios as they undergo
a chemical reaction, along with the phases of the substances
REACTANTS  PRODUCTS
 Phases: (s) solid, (l) liquid, (g) gas, and (aq) aqueous solutions [salt dissolved into water]
 Symbols over/under the arrow indicate catalysts or conditions for the reaction to
proceed
 Make sure the total number of each element is the same on each side of the arrow!
Ex.]
1. ___H2 + ___O2  ___H2O
2. ___N2 + ___H2  ___NH3
3. ___NaOH + ___CaCl2  ___NaCl + ___Ca(OH)2
4. ___C3H8 + ___O2  ___CO2 + ___H2O
5. ___C4H10 + ___O2  ___CO2 + ___H2O
6. sodium sulfate + calcium chloride 
sodium chloride + calcium sulfate
___
+ ___
 ___
+ ___
IV. Types of Reactions
The type of reaction occurring depends upon the type of reactants in the equation and the type of
substances desired for the products side of the equation. There are four major types of reactions:
A. Synthesis
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Combination reactions!
These combine elements, or small compounds, into a larger, single product
All should fit into the format below, where A and B are different elements or small
compounds and C is a combination of those elements/compounds
Format:
A + B  C
Ex.]
B. Decomposition
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A single compound is decomposed into simpler elements or smaller, separate
compounds
Opposite of Synthesis reaction
All should fit into the format below, where C is a combination of those
elements/compounds and A and B are different elements or small compounds
Format:
Example:]
C  A + B
C. Single Replacement
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Reactions where one element replaces another in a compound
Reactants are an element and a compound
Products are a new element and a new compound
Positive ions in a compound are replaced by metals
Negative ions in a compound may be replaced by nonmetal elements
Remember: positive ions always appear first in the formula; negative ions are second
Format:
AB + C  CB + A [where C = a metal]
AB + C  AC + B [where C = a nonmetal]
Example:]
D. Double Replacement
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Reactions where the positive ions from two separate compounds switch places to form
two new compounds
Reactants are two compounds
Products are two new compounds (different names)
Format:
AB + CD  AD + CB
[Notice: positive ions are first!]
Examples:]
V. Predicting Products
o Looking at the types of substances on the reactant side of the equation, predict the
products that will form, based on reactants and the type of reaction, then balance
the newly completed equation
o FIRST: identify the TYPE of reaction that will occur based on types of reactants!
o SECOND: write the formulas of the products [using subscripts!]
o THIRD: Balance the complete equation! [using coefficients!]
Examples:]