Topic 2 Formulas and Equations
Chemical Symbols and Formulas
Each elements has been assigned a unique 1, 2, or 3-letter Symbol for its identification,
and these name/symbols are given by the International Union of Pure and Applied
Chemists (IUPAC)
Formulas: show both symbol and numbers of the atoms present
Qualitative: show the symbol of the element
Quantitative: show numbers of the element
Coefficient: tells how many units of the formula are present, and it applies to th entire
formula
Monatomic:1 atom
Diatomic: 2 atoms
Polyatomic:multiple atoms
Ex: H2O
= 2 hydrogen atoms, 1 oxygen atom (read the subscripts)
Ex: CO
= 1 carbon atom, 1 oxygen atom (no subscript means 1 atom)
Ex: 3 H2O = 6 hydrogen atoms, 3 oxygen atom (subscript x coefficient)
Ex: 3 Mg (C2H3O2)2
Atoms:
= 3 Mg, 12 C, 18 H, 12 O (subscript x parenthesis x coefficient)
-neutral charge, monatomic element or diatomic element
Ex: Au, O2
Compound:-neutral charge, 2 or more elements bonded together
Ex: H2O, NaCl, (NH4)3PO4
Ions:
-either positive (lose electron) or negative (gain electron) charged
Ex: Na+, NO32-
Writing Formulas and Naming Compound
(use oxidation number, (charges))
Ionic compound: metal (positive charge) + nonmetal (negative charge)
(Binary compound: change ending to –ide)
Ex: NaCl Sodium Chloride
MgS
Magnesium Sulfide
CaBr2 Calcium Bromide
K2S
With polyatomic ions (Charges), use Table E
Ex: KOH Potassium Hydroxide NH4Cl
NaCN Sodium cyanide
SrClO4
Potassium Sulfide
Ammonium Chloride
Strotium Perchlorate
Covalent / molecular compound: nonmetal + nonmetal (No Charges)
Use prefixes (1=mon, 2=di, 3=tri, 4=tetr, 5=pent, 6=hex, 7=hept, 8=oct, 9=non, 10=dec)
*note: If only one atom of the first element is present, the prefix mono is not used.
Ex: CO
Carbon monoxide
N2O5
Dinitrogent pentoxide
The Stock System (Transition metals): have more than one oxidation number
Use Roman numerals (1=I, 2=II, 3=III, 4=IV, 5=V, 6=VI, 7=VII)
Ex: FeCl2
Iron (II) Chloride
Fe+2 Cl-1
FeCl3
Iron (III) Chloride
Fe+3 Cl-1
Polyatomic ions: [Table E]
Hydrates: compound with water
Anhydrates: compound without water
Ex: Al(ClO3)3 ● 6 H2O
Ex: Al(ClO3)3
Physical changes: anything that you can measure, such as phase change = melting or
boiling of water, sizes, temperatures, textures, etc.
Chemical changes: forming a new substance, such as burning a piece of paper or gasoline,
reacting with other chemical
Endothermic Processes [Table I]: processes that require energy, ∆H is positive, energy is
on the left side of the equation.
Exothermic Processes [Table I]: processes that release thermal energy, ∆H is negative,
energy is on the right side of the equation.
Type of reaction:
1. Synthesis (combining together)
A + B → AB
Ex: H2(g) + O2(g) → 2H2O(g)
2. Decomposition (breaking down)
AB → A + B
Ex: H2O(l) → H2(g) + O2(g)
3. Single Replacement A + BC → AB + C (One element and one compound on each side)
Ex: Zn + Cu(NO3)2 →Cu + Zn (NO3)2
4. Double Replacement AB + CD → AD + BC (Two different compound on each side)
Ex:AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)
Balancing Chemical Equations: left side of the equation is equal to the right side of the
equation
Balanced equation
Ex: C + O2 → CO2
1C, 2O
= 1C, 2O
Unbalanced equation
H2 + O2 → H2O
2H, 2O =2H, 1O