Chemical Names, Formulas & Equations
I. Chemical formulas & Names
A. Molecular/covalent formula– tells #’s & kinds of atoms in a single molecule of the cmpd.
1. subscript – number to the lower right of the symbol tell the number of atoms (or
molecules if it’s in parentheses)
2. Diatomic molecules- elements that can & do exist in the pure state when bonded
to another atom of the same type.
Memorize these that normally exist as a diatomic molecule: H2, N2, O2, F2, Cl2, Br2, I2 (S8 & P4)
3. Binary molecular cmpd (covalent bonds)
a. old system uses prefixes, like carbon dioxide CO2, carbon monoxide CO &
changes the ending of the second element to –ide p.213
b. Stock System – based on oxidation #’s
1) Oxidation number or state - created # - it’s the overall “charge”
of an atom after it has gained/lost e- …since covalently bonded atoms
don’t really lose or gain e- they use what it would be if they did!
--atoms in a pure element have an ox # of zero
--the more electroneg element will have a neg ox # equal to how many e- it needs to be stable
--the less electroneg. # will have a pos ox # equal to how many e- it would give up to be stable
--F has an ox # of -1
--O has an ox # of -2 with a few exceptions (cmpds with halogens ox #= +2, peroxides H2O2
ox # -1)
--H has an ox # of +1 w/nonmetals & an ox # of -1 with metals
--sum of ox #’s in a neutral cmpd = 0
--sum of ox #’s in a polyatomic ion = charge on ion
--ox # for a monatomic ion is the same as the charge
2) naming: element w/ +ox number then roman numeral of ox # then
the element w/ the –ox # with the ending changed to ide.
Example: phosphorus (III) chloride PCl3
phosphorus (V) chloride PCl5
in the old system they would be
phosphorus trichloride
phosphorus pentachloride
B. Ionic cmpds- shows formula unit - simplest ratio of cations (+) to anions (-)
1. monatomic ions – formed from a single atom (LIST!!!)
a. naming –name of element
b. if the cation has more than 1 possible ion form there will be a roman
numeral after it to indicate which ion form it is : lead (III) or lead (IV)
**Metals form +cations & lose e**Nonmetals form –anions & gain e2. Binary Ionic cmpds – made of 2 dif. ions
a) when they combine the sum of the charges must = zero
b) write +cation 1st
c) use the opposite charges as subscript (drop the signs)
Al+3 + O-2 = Al2O3
d) nomenclature – naming system
1) name of cation (roman numeral if
multiple possibilities) then name of
anion with ending changed to ide
2) Stock system adds roman numerals to indicate the ion’s
charge (for those that have multiples)
3) if an ion doesn’t have multiples then no rom. num.
CuCl2 = copper (II) chloride
3. Polyatomic ions – all are neg. except for ammonium NH4+ & most are oxyanions
(containing oxygen)
a. naming – name of +cation then name of polyatomic ion
p.209
p.211
p.235!
II. Chemical Equation- uses symbols & formulas to show the identities & relative amounts of reactants &
products in a chem reaction
A. How do you know if a chem reaction has occurred? Look for signs… but, be CAREFUL!
1. heat produced (light bulb – not)
2. light produced (light bulb – not)
3. gas formation (bubbles, odor) (mentos is soda – not)
4. precipitate formed (solid produced as a result of a chem reaction in solution & thenit
separates from the solution) – looks cloudy…. (milk into water – not)
5. color change (food coloring into water – not)
B. It’s a symbolized statement of a chemical reaction.
C. quantitative
D. must follow the Law of Conservation of Matter: “Matter can neither be created nor destroyed
just changed from one form to another.” So, the mass of the reactants must equal the mass of
the
products.
E. Must represent all substances involved in symbol form, written correctly according to ox. #’s.
F. Physical states can be designated: (s), (l), (g), or (aq) aq stands for aqueous which means the
substance is dissolved in water….if you evaporate the water you should have the substance
left over
G. yield sign indicates that a reaction has occurred & indicates the direction of the reaction
H. coefficients (large numbers in front of reactants & products) indicate RELATIVE amounts of
reactants & products (coefficients indicate smallest numbers of moles of atoms…. that will
satisfy
Law of Cons. of Matter)
I. Parts of the equation:
1. p.246 – chart!
J. How to write an equation:
1. write the word equation
2. write the unbalanced equation making sure all formulas are correct
3. balance the equation
K. From the coefficients in a chemical equation you can find the masses of the reactans &
products.
H2 (g) + Cl2 (g)→ 2HCl (aq)
How many grams of each are present?
III. Balancing chemical equations
A. tips
1. check for diatomic molecules
a. if these elements appear by themselves in an equation they must be written as diatomic
molecules with a 2 subscript
b. MINOH balance metals, ions, nonmetals, then O & H
c. recount all atoms
d. balance equations by changing coefficients NEVER by changing subscripts
e. if atoms are not balance at this point there is a problem somewhere
f. if every coefficient will reduce, rewrite it in the simplest whole-number ratio
it’s not properly balance if it’s not in the simplest whole-number ratio
IV. Types of chemical reactions (How do you know what will react & what won’t?)
A. Synthesis reactions A + X → AX where A & X can be elements or cmpds & AX is a cmpd
1. 2 or more substances combine to form 1 complex substance
2. ex: Mg + O → MgO
H2O + SO3 → H2SO4
3. almost all metals will react to form oxides & sulfides
4. Combustions reactions – a substance combines with oxygen releasing a large amt of E in the
form of light & heat
The combustion of hydrogen ---think Hindenberg! (it produces water vapor)
H2 (g) + O2 (g) → H2O (g)
The combustion of a hydrocarbon (propane, gasoline…they contain C & H only)
C3H8 (g) + O2(g) → CO2(g) + H2O (g)
B. Decomposition Reactions AX → A + X where A & X can be elements or cmpds & AX is a cmpd
1. a single cmpd reacts to form 2 or more simpler substances
2. 6 kinds of decomp reactions
a. metallic carbonates when heated form metallic oxides & CO2
Li2CO3 → Li2O + CO2
b. (many) metallic hydroxides when heated form metallic oxides & water
LiOH → Li2O + H2O
c. metallic chlorates when heated form metallic chlorides & oxygen
LiClO3 → LiCl + O2
d. (some) acids when heated form nonmetallic oxides & water
H2CO3 → CO2 + H2O
e. (some) oxides when heated decompose
HgO → Hg + O2
f. electrolysis – the decomp of a substance by an electric current
C. Single Replacement Reactions A + BX → AX + B
1. one substance replaces another (usually require less E than syn. or decomp. reactions)
2. kinds
a. a metal in a cmpd is replaced by a more active metal (see activity series chart p.266)*
Al + Pb(NO3)2 → Pb + Al(NO3)3
*activity series – list of elements in order of the chemical reactivity
-useful in predicting whether a chem reaction will occur
-most active element at top can replace each of the elments below it from a cmpd in a
single replacement reaction
b. (1/2) the hydrogen in water replaced by a metal
Na + H2O → NaOH + H2
c. hydrogen replaced by metal in an acid
Mg + HCl → MgCl2 + H2
d. a halogen in a cmpd is replaced by a more active halogen
Cl2 + KBr → KCl + Br2
D. Double Replacement Reactions AX + BY → AY + BX
1. Ions of 2 cmpds in solution exchange places
a. one of the cmpds formed is usually a substance that leaves the reaction envr. (as a
precipitate or an insoluble gas that bubbles out) or a molecular cmpd (usually water)
b. the other cmpd is usually soluble & remains in solution
c. ex: NaCl (aq)+ AgNO3 (aq) → NaNO3 (aq)+ AgCl (s)
AgCl is the precipitate
FeS (s) + HCl (aq) → H2S (g) + FeCl2 (aq)