Calculating & Naming Compounds

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Transcript Calculating & Naming Compounds

Unit3 – Lecture 8
Recap – Bonding Occurs…
 …to fill the outer level of electrons of elements
 you can predict bonding by observing trends on
the periodic table:
 type of element: metals, non metals, etc
 valence electrons: for lewis diagrams
 oxidation #: criss-cross method
Counting Atoms
 Chemical Formula -
shows how many of
which atoms are in a
molecule
 Coefficient - placed in
front of a molecule to
show more than one
molecule
 Subscript - number
placed below and
behind a symbol to
show how many of
which atoms are present
3H2O
Counting Atoms
 Diatomic Molecule - two
atoms of the same
nonmetal (usually in gas
form) that have bonded
together
 Reactive nonmetals will
bond with one another if
no other substance is
available for bonding
H2 N 2
O2 F2
I2 Cl2
Br2
Polyatomic Ions
 a group of atoms that behave
as one atom
 keep together as a unit
 if more than one polyatomic
ion is present in a molecule,
parentheses set it apart
 Still use a subscript to
show how many
 How many (OH)?
Ca(OH)2
NH4Cl
Common Polyatomic Ions
 See your packet…
How Many?
 Making formulae –
the “Criss Cross” Method background:
 uses oxidation numbers to predict # of each element
in a compound when 2 elements bond
 Oxidation # Review:
 + or – sign, indicates # of electrons that will be
gained or lost
 written like a charge in the upper right
 always included [given to you] if you have
polyatomic ions
Oxidation/Charge Numbers
+1 +2 ----------------------------------------- +3
4 -3 -2 -1 0
+/-
Oxidation #s – cont’d
 Transition metals have more than one oxidation
number!!!!
 Fe[III] = Fe+3 = Iron with +3 oxidation number
 Fe[II] = Fe+2 = Iron with +2 oxidation number
 Mn[II] = Mn+2 = Manganese with +2 oxidation number
 Mn[III] = Mn+3 = Manganese with +3 oxidation number
Making Formulae –
the “Criss-Cross” Method
 cation first – write element & oxidation #
 anion next – write element & oxidation #
 without the + or – sign
 write the oxidation # from one symbol
on the other as a subscript
 remember to add parentheses around
polyatomic ions
 don’t write the #1, it is implied
 reduce any evenly-divisible subscripts
Examples
 Bond btw Aluminum and Oxygen
 Bond btw Aluminum and Carbonate [CO3]-2
Examples
 Bond btw Aluminum and Oxygen
 Al +3
O -2
 Al2O3
 Bond btw Magnesium and Borate[BO3]-3
 Mg +2
(BO3) -3
 Al3(BO3)2
Practice
Complete practice problems 1-9 in your packet.
Reverse Criss-Cross
 use to find oxidation on atoms in a compound.
 PCl3  P Cl3
 So… P is 3, and Cl is 1
 for transition metals – VERY useful
 Ti Cl2  Ti
Cl2  So… Ti is 2 and Cl is 1
 Oxidation for Ti is +2 
Binomial Nomenclature
 a “two name” “naming” system
 like Genus species from biology….
 Used to differentiate between elements and
compounds
 Fluorine (an element) vs
Fluoride (part of a compound)
 Never change the name of a Polyatomic Ion
 Big difference between Sulfide, Sulfite, and Sulfate
Naming Ionic Compounds
 List the positive ion (or metal) first
 ***Use Roman Numerals to show the Oxidation
number of a transition metal
 Name the negative ion (or nonmetal),
changing the ending to –ide
 “Oxide”
 “Sulfide”
 “Phosphide”
 Ex: FeO / Fe2O3
 = Iron II Oxide / Iron III Oxide
Practice
 Complete practice – Naming Ionic Cmpds page 14
Naming Polyatomic Compounds
 cmpd is polyatomic if there are more than 2 elements
You will be given the names for common polyatomics.
Still only 2 words in the name
 first term = positive ion name
 second term = negative ion name
 if second term is NOT a polyatomic,
change ending to -ide
 if the second term is a negative polyatomic,
do NOT change the ending
Practice
 complete the practice problems 1-3.
Homework
 finish any practice problems from lecture
 complete Naming IONIC Compounds w/s [1-14] ONLY
HONORS ONLY:
 make 2 sets of polyatomic ion cards [for the ten given]
 name  formula [should still include charge…]
 name  charge
Naming Covalent Compounds
 Prefixes are used to show how many of which atoms
 = number terms from Greek / Latin
 Write the name of the cation [or most positive]
 only add a prefix for the first atom if
there is more than one
 Write the name of the anion [or most negative]
 add a prefix to tell how many are present
 change the ending to -ide
Numbering Prefixes
1 – Mono2 – Di3 – Tri4 – Tetra5 – Penta-
6 – Hexa7 – Hepta8 – Octa9 – Nona10 – Deka-
Practice
 What is the name for N2O4?
 non-metal + non-metal…so covalent
 Dinitrogen Tetraoxide
 What is the name for Na2S?
 metal + non-metal = ionic
 Sodium Sulfide
 What is the name for CO2?
 non-metal + non-metal = covalent
 Carbon Dioxide
Practice – cont’d
 What is the name for (NH4)2O?
[hint: you need to know what (NH4) is…]
 Nitrogen Hydrogen Oxide
 Mononitrogen Tetrahydrogen Oxide
 Ammonium Oxide CORRECT!!!!
 Diammonium Oxide
 Ammonium Oxalate
Practice – cont’d
Al2S3
CrO
Lead (II) oxide
PbO2
(NH4)2S
Ca(OH)2
Iron (II) cyanide
Fe(NO3)3
Aluminum sulfide
Chromium (II) oxide
PbO
Lead (IV) oxide
Ammonium sulfide
Calcium hydroxide
Fe(CN)2
Iron (III) nitrate