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Unit 3: Chemical Formulas & Equations
EQ: What kind of PRECISE information can a chemical reaction depict for us?
the LANGUAGE of ChEmIsTrY
* Chemical Symbols: 1,2, or 3 letters that represent an element’s atomic number (specific element) * we already saw basic symbols -- periodic table & Table s
the LANGUAGE of ChEmIsTrY
* Diatomic Molecules: * H O F Br I N Cl = the 7 elements that exist as diatomic
molecules (or Br I N Cl H O F) * Having 2 atoms of identical elements bonded together * contain subscripts in their chemical formulas * ** H2 O2 F2 Br2 I2 N2 Cl2
the LANGUAGE of ChEmIsTrY * Compounds: Tell us both qualitative and
quantitative information via their chemical Formulas
* Qualitative: info not counted or measured,
like what elements are in the compound
* Quantitative: info countable or
measurable like # atoms of each element
in a compound
* what type of qualitative and quantitative info are
these two chemical formulas depicting?
the LANGUAGE of ChEmIsTrY Types of Formulas: * 1) Empirical à represents the simplest integer ratio
in which atoms combine to form a compound * **think Least Common Multiple (math) * i.e. MgCl2 ratio is 1:2, aka 1Mg atom for every 2 Cl atoms
* 2) Molecular à of a molecule (group of bonded
atoms that compose a discrete substance); can be a multiple of the empirical formula * i.e. Glucose = C6H12O6, which is 6 times the empirical
formula of CH2O
Atoms, Compounds, & Ions
Atoms are electrically ________! J Ions are ________ atoms/particles! à Umm, so tell us something we
don’t know!? LOL
Charges of Ions: (we ALSO know this!) * Metals = (tend to be) POSITIVE (+) * Non-Metals = (tend to be) NEGATIVE (-)
Atoms, Compounds, & Ions
Examples: (what types of ions/charges do these become) * 1) Mg * 2) Al * 3) Cl * 4) P * 5) Rb * 6) S
* Mg2+
* Al3+ * Cl-
* P3- * Rb+
* S2-
ßAtoms Ions à
Polyatomic Ions **Check out Reference table E** * Poly – more than one, ATOMIC – atoms, so group
of atoms bonded together that posses a charge (are IONs) * What about the (parentheses)?!? ** PREVIEW
* ex: (NH4)3PO4 Ammonium Phosphate à locate on table
* THREE NH4+ ions
* ONE PO43- ions
* TOTALS: * 3 N’s & 12 H’s * 1 P & 4 O’s
Coefficients JUST. LIKE. IN. MATH.
WHOAHHHHHH! J * The # in front of a chemical formula * examples: what do these mean? * 2x + 5…. * 5(x2 + 10x – 3)…
* so what do you think THESE mean? * 2H2O * 4Mg(NO3)2
Coefficients How many of each type of atom are in the following molecular compounds?
Ca(NO3)2 3Ca(NO3)2 K3PO4
5K3PO4
* 1 Ca, 2 N’s, & 6 O’s
* 3 Ca’s, 6 N’s & 18 O’s
* 3 K’s, 1 P, & 4 O’s
* 15 K’s, 5 P’s & 20 O’s
Hydrates Water can get bound to an ionic solution, form a crystal lattice with the solution, & then get trapped….aka, a Hydrate. Example: Barium Chloride, BaCl2, traps 2 water molecules, so BaCl2�2H2O
Copper Sulfate, CuSO4 has 5 hydrates, what is it’s molecular formula going to look like?
CuSO4�5H2O
Equalizing Charges – “Matchmaker” Status aka…How to make compounds electrically NEUTRAL: * 1) Identify the POSITIVE ION & CHARGE
ex) Sodium = Na+
* 2) Identify the NEGATIVE ION & CHARGE ex) Chlorine = Cl-
* 3) Balance the CHARGES Na + & Cl – are a 1:1 ratio (1 Positive, 1 Negative) so they are neutral when combined together as NaCl * 4) If the charges are not equal, use the “criss-cross”
method to balance them out… Mg2+ & Cl - … becomes MgCl2 **show on board**
Equalizing Charges – “Matchmaker” Status How do we play matchmaker with these examples?
1) Al & OH à
2) Ca & ClO3 à
3) K & PO4 à
* Al3+ & (OH)- * Al(OH)3
* Ca2+ & ClO3-
* Ca(ClO3)2
* K+ & PO43-
* K3PO4
Naming Compounds (IUPAC) - IONIC * 1) Identify the POSITIVE ION
à usually metallic ex) Na = SODIUM * 2) Identify the NEGATIVE ION
à usually Non-metallic ex) Cl = CHLORINE * 3) Keep the name of the positive ion & change
the name of the negative ion: ex) Chlorine = Chloride
Therefore, our name is Sodium Chloride
(IUPAC) IONIC EXAMPLES How do we name the following example compounds?
1) KCl à
2) MgS à
3) AlNà
* Potassium Chloride
* Magnesium Sulfide
* Aluminum Nitride
Naming Compounds with Polyatomic Ions
* SAME STEPS à some things to take note of: * NAMING: metallic ion + polyatomic
ion * keep BOTH metallic/nonmetallic ion names
ex) KNO3 à Potassium + Nitrate
so NAME = Potassium Nitrate
Naming Compounds with Polyatomic Ions
* *most polyatomic ions are NEGATIVE ions, with important exception = NH4
+ (ammonium) * when combined with a non-metal, the ending
changes to –ide also (just like we do regularly)
* NH4Cl
* NH4NO3
* Ammonium Chloride * Ammonium Nitrate * no change*
the “STOCK SYSTEM”-TRANSITION METALS
* Transition Metals can have more than one common charge
* Ex) Iron à +2 or +3 * if given Iron Chloride as name, which charge is it?
USE ROMAN NUMERALS * ex) Iron (II) Chloride = Iron +2 oxidation state * Formula? =
* Formula for Iron (III) Chloride = ?
* FeCl2
* FeCl3
ChEMiCaL Reactions & Equations
* Physical Change: change in appearance of substance, NOT the formation of something new
* ex) Ice melting…
solid à liquid
* Chemical Change: change in identity between REACTANTS & PRODUCTS * Chemical Reactions define
chemical changes
cHeMiCaL Reactions & Equations
Burning of Carbon Dioxide
carbon + oxygen à carbon dioxide
C(s) + O2(g) à CO2(g)
reactants à products
ChEmIcAl Reactions & Equations Endothermic rxns: * require energy for rxn. to
occcur * reactants ABSORB
energy * ex) cooking, ice melting
Exothermic rxns: * RELEASE of
thermal energy during rxn * ex)burning CO2 ,
freezing of water
Balancing CHeMiCaL Reactions Law of Conservation of Mass: matter is neither created nor destroyed in chemical reactions…aka, numbers & kinds of atoms don’t change
C + O2 à CO2 1 C atom + 2 O atoms à 1 C atom 2 O atoms
H2 + O2 à H2O what’s wrong? we’re missing another Oxygen!
2H2 (g) + O2 (g) à 2H2O (g) 4 H’s, 2 O’s à 4 H’s 2 O’s A Conservation of ATOMS =
BALANCED J -- charge/energy/atoms
Balancing CHeMiCaL Reactions How do we balance POLYATOMIC IONS in reactions??
AgNO3 + MgCl2 à Mg(NO3)2 + AgCl *Q?
2AgNO3 + MgCl2 à Mg(NO3)2 + 2AgCl
Other example: C3H8 (g) + O2 (g) à H2O (g) + CO2 (g) *Q?
C3H8 (g) + 5O2 (g) à 4H2O (g) + 3CO2 (g) #C = 3 à #C = 3 #H = 8 #H = 8 #O = 10 #O = 10
SYNTHESIS REACTION A + B à AB
When two or more reactants combine to form a single product = synthesis, or combination reaction examples: * 2H2(g) + O2(g) à 2H2O(g)…formation of water * 4Fe(s) + 3O2(g) à 2Fe2O3(s)….rusting of iron * CO2(g) + H2O(l) à H2CO3(aq)….involving cmpds
DECOMPOSITION REACTION AB à A + B
When a single compound breaks down into two or more simpler substances = decomposition, or analysis reaction examples: * H2O(l) à H2(g) + O2(g)…decomp of water
* CaCO3(s) à CaO(s) + CO2(g) … 1 cmpd à 2 cmpds
SINGLE REPLACEMENT REACTION A + BX à B + AX
When one element replaces another element in a compound = single replacement reaction example: * Cu(s) + 2AgNO3(aq) à Cu(NO3)2(aq) + 2Ag(s)
(what’s happening)…copper wire put in silver nitrate solution, silver crystals form (solid) on wire and solution becomes blue
SINGLE REPLACEMENT REACTION * check out TABLE J****Activity Series * If a METAL or NONMETAL is arranged below
the element in question, then it WILL REACT * If it is NOT below it, then it WILL NOT replace the
element in the reaction. examples: Zn + Cu(NO3)2 à Cu + Zn(NO3)2 ….WILL REACT Cu + Zn(NO3)2 à No reaction F2 + 2NaCl à Cl2 + 2NaF … WILL REACT Cl2 + NaF à No reaction
DOUBLE REPLACEMENT REACTION AB + CD à AD + CB
When two compounds ‘SWAP’ components = double replacement reaction; usually produce precipitates, a gas, or molecular compound (like water) example: AgNO3(aq) + NaCl(aq) à AgCl(s) + NaNO3(aq) (what’s happening)…silver nitrate and sodium chloride are mixed, and white precipitate of silver nitrate forms (solid) and silver chloride is produced
UNKNOWNS ?? Since LAW of CONSERVATION OF MASS tells us that both sides of a reaction must have equal parts of matter, we can determine what reactants or products are missing from a chemical reaction.
2Na + 2H2O à X + 2NaOH # Na’s = 2 à # Na’s = 2 # H’s = 4 # H’s = 2 # O’s = 2 # O’s = 2
what’s missing?? = H2 = X
UNKNOWNS ?? We can also determine the missing MASSES of each side of our chemical equations: if 103.0 g potassium chlorate are decomposed to form 62.7g of potassium chloride and oxygen gas, how many grams of oxygen are formed? (given equation)
2KClO3 à 2KCl + 3O2 mass KClO3 = 103.0g mass KCl = 62.7g mass O2 = ? *total mass must be equal on both sides, therefore:
103.0g = 62.7g + mass of O2 mass of O2 = 103.0g – 62.7g = 40.3g