Unit 5
U: 4, 5, 6
A: 1, 2, 3, 4, 5
DATE:________________
INTERPRETING A CHEMICAL FORMULA
X# +/―
Identify charge state of Ions. DO NOT APPEAR IN
CHEMICAL FORMULAS. ANY PARTICLE with a
charge is an ion. Ion charge are canceled out as
compounds are STABLE
Subscripts, X#
Denote # of atoms/ions/polyatomics present. They
Distribute only to what they are written next to.
Note:1's are assumed, not written as subscripts
~ i.e. H2O not H2O1
Note: Use ( ) to keep polyatomic ions distinct. DO NOT
distribute to polyatomic ions in parentheses.
~ i.e. (C2O4)2 = 4 = C, 8 = O
≠ C4O8
Overview: Since there are two different types of elements: metals and nonmetals,
there are three possible combinations of those two types of elements:
A. metals + nonmetals: combine to form ionic compounds and will the
focus of this.
B. nonmetals + nonmetals: combine to form molecular compounds which
are held together by covalent bonds. Electrons are shared rather than
transferred. We will name binary molecular compounds in this unit, and
then come back to understand the bonding mechanism further in after
spring break.
C. metals + metals: metals do not chemically combine to form compounds,
they simply mix together to form alloys. Again we will come back to
understand the bonding mechanism further in after spring break.
Superscripts,
Compare and
Contrast:
Ionic Compounds (A above)
Molecular Compounds (B above)
Made of?
What are the
electrons doing?
metal + nonmetal
transfer electrons
metals lose and become + ion (cation)
nonmetals gain and become − ion (anion)
always written in lowest whole # ratio
metal (positive ion) always first
nonmetal (negative ion) always second
metals require roman numeral to indicate the charge (group 1A, 2A,
and Al, Ag, Zn, Cd do NOT use Roman #)
prefixes NOT used (except within a few polyatomic ions)
nonmetal + nonmetal
electrons are shared
no ions are formed
Formulas?
Order of formula?
Using roman #’s?
Using prefixes?
Naming?
Particles are called?
Polyatomic ions end
metal keeps its name
nonmetal ends in –ide
polyatomics end in –ate and –ite (a few in –ide)
individual particles are called formula units (“ionicules”)
in –ite and –ate (a few end in –ide)
IDENTIFYING TYPE OF COMPOUND FROM FORMULA
Formula contains
Compound is:
Starts H
1 M element + 1 NM element
1 M element + 2 (or more) NM’s
2 NM’s
Acidic
Binary Ionic
Poly Ionic
Molecular (Covalent)
may not always be lowest ratio
Less electronegative atom written first
no roman numerals used since the atoms do
NOT have charges.
prefixes are used to indicate the number of
atoms present in the compound
for binary compounds, the second element
listed ends in –ide
individual particles are called molecules
NA (not applicable)
IDENTIFYING TYPE OF COMPOUND FROM NAME
Name
Begins with prefix hydro- and ends Acid
No prefixes of hydro and ends Acid
No prefixes and doesn’t end Acid
Makes use of Greek Prefixes
Compound is:
Binary Acid
Poly Acid
Ionic
Molecular (Covalent)
Binary Ionic Nomenclature - As you know, metals like to lose electrons, and nonmetals like to gain electrons. Thus when metals and
nonmetals come together, they can each reach electronic nirvana. Remember that the number of valence electrons determines the
number of electrons that will be lost or gained. This is correlated to the main group # (denoted #A) that the element is in on the
Periodic Table. The Table is grouped this way because elements in the same column behave the same way chemically.
−
−
No atom can randomly throw off e or gain e unless there is some other atom around to accept or provide them. So Na is "standing on
−
the corner, feeling lousy” with its 1 extra valence e and along comes chlorine, “feeling lousy” since it would really like to have one
−
more e−. They get together and make the transfer of e with each atom becoming an ion (and then the opposite charges hold them
together), making an ionic compound with the NaCl unit held together by an ionic bond.
Using Groups: metals 1A, 2A, Al, nonmetals 5A, 6A, 7A
−
What if sodium wanted to hang around oxygen instead? Na would give up 1e and feel good, but not completely satisfy the oxygen who
−
−
wants to get 2e . So Na has to bring its "sister or brother" to hang with the oxygen atom to provide the total of 2e thereby satisfying
the O, making the compound Na2O.
This is the start of writing the chemical formulas for ionic compounds. Remember that the main group that the atom is in on the Periodic
Table tells us how many valence electrons an atom has which impacts how many e- that atom wants to lose or gain which results in a
particular ion. The short-hand way to write chemical formulas for ionic compounds (remember this is just metals + nonmetals) is to look
at the combination of the two ions and “criss-cross” the correct number of each ion so the total positive charge will be equal (though
opposite) to the total negative charge.
The
players
(atoms)
Na & Cl
Na & O
Na & P
The ions
they
want
to form
+ −
Na Cl
+ 2−
Na O
+ 3−
Na P
Ba & F
Ba & S
Ba & N
Ba F
2+ 2−
Ba S
2+ 3−
Ba N
2+
−
The method these atoms (players) must combine to ensure that the number of
electrons transferred satisfies both players (atoms).
The resulting
Chemical formula
(the team)
Since the +/− charges are equal, only one of each ion is needed to satisfy; no subscripts
Two sodiums needed to make 2+ to balance 2−. Use the “criss-cross” method.
Three sodiums will provide a total of 3 electrons and ending up with a 3+ charge which
balances the phosphorus’ need for three electrons and a 3− charge. Use the “crisscross” method.
Two fluorines needed to make 2− to balance the 2+. Use the“criss-cross” method.
Since the +/− charges are equal, only one of each ion is needed to satisfy; no subscripts
Three bariums will provide a total of 6 electrons (6+ charge) which will satisfy two
nitrogens that need a total of 6 electrons (6− charge). Use the “criss-cross” method.
NaCl
Na2O
Na3P
Sodium chloride
Sodium oxide
Sodium phosphide
BaF2
BaS
Ba3N2
Barium fluoride
Barium sulfide
Barium nitride
A few reminders:
•At this point you have the tools needed to combine elements in
columns 1A, 2A, and Al with columns 5A, 6A, and 7A.
•Notice that the metal (+ ion, cation) is always written first, and
the nonmetal (− ion, anion) is always written second.
• Be sure and pay attention to upper and lower case letters, Cs
and CS do NOT have the same meaning.
• Remember that the placement of numbers around a symbol
have very particular meanings
2+
charges are written as superscripts (top right, X )
number of ions present in the formula are written as
subscripts (lower right, X3)
The name of the
ionic compound
CRISS – CROSS METHOD
(1) Write the symbol and charge above the metal/ammonium cation first, then
symbol and charge for the anion.
*For Acids – remember hydro(root )ic = monatomic;
(root )ic = rootate polyatomic; (root) ous = rootite polyatomic;
(2) Crisscross the charge numbers as subscripts (using parentheses around
polyatomic ions when they have a subscript applied to them)
Ca2+ CO32-
Ca2 (CO3)2
(3) Get rid of any “1’s” as the subscript. And be sure to “simplify” the terms of the
subscripts if necessary
Ca2 (CO3)2
CaCO3
So what about the rest of the metals…
Using Roman Numerals - So far the discussion has included only some of the metals of the periodic table. Now will to look at the transition
metals and the “other six” metals under the staircase ( 31Ge, 50Sn, 51Sb, 82Pb, 83Bi, 84Po). Because these elements are metals, they must
lose electrons, but because they have transition metal electrons (those 10 electrons stuffed deep inside in the d-block) they can lose
varying amounts of electrons producing ions that are “sort-of” satisfied.
What to do with an atom such as lead? The presence of transition metal electrons (those 10 electrons stuffed deep inside the d-block) in
lead cause it to be able to lose either 2 or 4 valence electrons and thus it can form, 2+ & 4+ ions. Since you have no way of predicting
which of these two options occurs, the name of a lead chloride compound must give more information or you wouldn’t be able to tell
which lead ion has formed. That information comes in the form of a Roman Numeral indicating the charge.
The
players
(atoms)
Pb & Cl
The
ions
they
want
to
form
+? −
Pb Cl
The method these atoms (players) must combine to ensure that the number of electrons
transferred satisfies both players (atoms).
The resulting
Chemical
formula (the
team)
Without being told the charge on the lead, you would have no way of knowing what charge
is formed.
So you first need to be told it is lead (II) chloride or lead (IV) chloride, so you need the name.
The Roman numeral tells you the + charge on the lead. NOT THE # OF LEADS!!!!!!!!!!!!
The name of the
ionic compound
The players
(atoms)
The ions
they want
to form
Lead(II) chloride
Pb & Cl
Pb Cl
Lead(IV) chloride
Pb & Cl
Tin (IV) oxide
Sn & O
Sn O
The method these atoms (players) must combine to ensure that the
number of electrons transferred satisfies both players (atoms).
The name of the
ionic compound
Lead(??) chloride
The resulting
chemical formula
(the team)
2+
−
Two chlorines (−1 each) needed to satisfy the one lead
PbCl2
Pb Cl
4+
−
For lead (IV) chloride the charge on the lead is 4+ thus 4 chlorines are
needed to satisfy the
PbCl4
4+
2−
If you criss-cross this time the tin and oxygen would combine as Sn2O4
however you must write the chemical formula in the lowest whole
number ratio. So reduce and write the formula as shown in the last
column.
SnO2
Working Backwards: This might get tricky when given the formula and asked to determine the correct name.
The
correct
formula
NiF3
The
charge
on
nonmetal
−
F
CrP2
P
Cu2S
S
3−
2−
The total
negative
charge
three F−
= −3 total
3−
two P
= −6
2−
one S is of
course a
charge of −2
must balance the total positive charge
The name of the ionic
compound
Since the fluoride carries a 1− charge, 3 of them × 1− equals 3−, and the
nickel ions total charge must be opposite in sign, but equal in magnitude,
thus Ni must be 3+, resulting in nickel(III) fluoride
nickel(III) fluoride
Since the phosphide carries a 3− charge, 1 of them × 2− equals 2−, and the
chromium ions total charge must be opposite in sign, but equal in
magnitude, thus Cr must be 6+, resulting in chromium(VI) oxide
chromium (VI) phosphide
Since the sulfide carries a 2− charge, 1 of them × 2− equals 2−, and the
copper ions total charge must be opposite in sign, but equal in magnitude.
Thus 2 copper ions × “what charge” = 2+? Thus the copper must be 1+,
resulting in copper(I) sulfide
copper (I) sulfide
Beyond Binary Ionic Compounds – Using Polyatomic Ions - As you know, binary ionic compounds
contain only two different elements. But many compounds contain more than two different
elements. Two or more different elements hook together to make an ion (usually an anion)since it is made of may atoms, it is called a polyatomic ion.
2−
2−
For example SO4 which is called sulfate or SO3 called sulfite. You have a list of polyatomic ions
provided to you. In this course you will not be required to memorize them. You can always refer
to the chart.
What’s going on with the names? Notice the names - single element anions carry the name of the
element with an -ide on the end. Most of the polyatomic ions end in -ite, or -ate.
•nitrite, nitrate NO2− NO3−
−
−
−
−
•chlorite, chlorate (hypochlorite, perchlorate) ClO2 ClO3 (ClO , ClO4 )
There are a few exceptions that end in -ide
−
−
2−
• hydroxide OH
• cyanide CN
• peroxide O
And one that ends –ium, which is the only cation polyatomic you are provided
+
• ammonium NH4
Problems to avoid - Be alert for the need with parentheses when the compound contains more than
one polyatomic.
• magnesium nitrate should be Mg(NO3)2 not MgNO32
• aluminum cyanide must be Al(CN)3 not AlCN3 leaving the ( ) off would mean 3 N’s
and 1 C, but you need 3 CN’s
When you are working backwards and trying to figure a Roman numeral polyatomic ions
sometimes can be tricky.
• Suppose you are given the formula Co2(SO4)3 and asked for the name.
o You could use either the “uncriss-cross and check” or the “start with the
negative ion to determine the total charge” method, and hopefully you will
end up with cobalt(III) sulfate.
• What if you were to determine the name of CuNO 3 ?
o Be careful with the “3”. You may be tempted to think of having 3 nitrates, but
there is only one there, so the negative charge is 1− not 3− .
o Thus the copper has a 1+ charge and the nitrate a 1−
o In other words, don’t uncross-cross the 3.
Ammonium – Be alert for the positive polyatomic ion - Look on your Polyatomic ion chart and see
that there is one important exception on the polyatomic ion chart, the positive polyatomic
+
ammonium NH4 we will treat it just like the metallic ions.
• ammonium hydroxide
NH4OH
• ammonium sulfate
(NH4)2SO4
• ammonium chloride
NH4Cl
Polyatomic Formula
NH4+
Polyatomic Name
Ammonium Ion
C2H3O2- OR CH3COO-
Acetate Ion
BrO3-
Bromate Ion
IO3-
Iodate Ion
ClO4-
Perchlorate Ion
ClO3-
Chlorate Ion
ClO2-
Chlorite Ion
ClO-
Hypochlorite Ion
HCO3-
Bicarbonate Ion
OR
Hydrogen Carbonate Ion
CO32-
Carbonate Ion
NO3-
Nitrate Ion
NO2-
Nitrite Ion
HSO4-
Bisulfate Ion
OR
Hydrogen Sulfate Ion
SO42-
Sulfate Ion
SO32-
Sulfite Ion
PO43-
Phosphate Ion
CrO42-
Chromate Ion
Cr2O72-
Dichromate Ion
OH-
Hydroxide Ion
C2O42-
Oxalate Ion
O22-
Peroxide Ion
MnO4-
Permangate Ion
SCN-
Thiocyanate Ion
CN-
Cyanide Ion
Polyatomic Reference
As standard Chemistry students you are not required to
memorize polyatomic ions. You must however, be
able to use the reference left appropriately,
especially their spellings. YES YOU WILL RECEIVE THIS
REFERENCE FOR EVERY TEST AND EVEN YOUR FINAL.
Binary Molecular Compounds - The term binary means – involving two elements. Thus a molecular compound is made
of two (only two, and not three) different nonmetals. We will not learn any systematic method of naming
molecular compounds with more than two different elements. Instead, we will refer to them by their common
names, like sugar C6H12O6.
GREEK PREFIXES
# of atoms
Greek Prefix
1
mono2
di3
triThe first element listed retains the same name, and the second element changes its ending into ____ - ide
4
tetraThere is no need to consider any charge since when nonmetals bond with other nonmetals, electrons are shared,
5
pentaand no ions are formed. Instead, prefixes are used to indicate the subscript attached to the element.
6
hexa7
heptaFor example
8
octacarbon monoxide, CO
• You can see that themono- is never used for the first element
9
nonadinitrogen monosulfide N2S
• You can see that the prefixes are sometimes modified to align themselves English language standards.
10
decacarbon dioxide, CO2
smoother. (mono oxide = monoxide)
NOTE: When apply ing is never a double
disulfer pentoxide S2O5
vowel like –oo- , i.e. monooxide =
incorrect; monoxide = correct
Acids (Compounds that sit the fence between ionic and covalent) - Acids are compounds that are molecular in make-up (made of nonmetals with covalent
bonds), but when put into water, they separate into ions, thus behaving like ionic compounds. Most importantly, memorize or learn the scheme for
naming acids found below.
QUESTION METHOD: Formula → Compound Name
Compound is an
Acid
Anion
-ide
-ite
-ate
Compound is Binary
Name ends -ide
DISTILATION OF COMPOUND NOTES
QUESTION METHOD: Compound Name → Formula
End Acid?
Compound
is Ionic
yes
no
Prefix Used?
Start with Hydro-?
no
yes
no
yes
Name Cation
then Anion
Compound is Binary Molecular
Binary Molecular
Prefixes = Subscripts
DO NOT CRISS-CROSS
X [prefix X] Y [prefix Y]
Oxy Acid
(Contain O’s)
Subscript on H is charge
of polyatomic anion
H[anion charge] Anion
Roman Numeral Used?
yes
no
Ionic
Determine charge on cation & anion then
criss-cross charge #’s. Be sure to simplify.
X [anion charge] Y [cation charge
Be sure to use ( ) around polyatomics
if there is more than 1.
Acid name
hydro-(stem)-ic acid
(stem)-ous acid
(stem)-ic acid
Binary Acid
(Doesn’t contain O)
Subscript on H is charge
of anion
Compound
is Ionic
-1st Element = element name;
-2nd Element = root followed by = -ide.
-Use greek prefixes in the name
i.e. N2O3 = dinitrogen trioxide
H [anion charge] Anion
Remember
-ic Acid = -ate ion
-ous Acid = -ite ion
Name Cation with Roman
Numerals in ( ) to denote
charge #, then the anion.
Stock Ionic
Cation charge equals roman numeral
value. Determine anion then criss-cross
charge #’s. Be sure to simplify.
X [anion charge] Y [cation charge]
Be sure to use ( ) around polyatomics
if there is more than 1.
Name Cation then Anion
Name Cation with Roman
Numerals in ( ) to denote
charge #, then the anion.
Note: “P = d-block” is really asking if P is a metal that has only one
possible charge—if it is so, no roman numeral is necessary.