Unit 5
Chemical Names
and Formulas
Noble Gases
• Only the noble gases can exist as single
atoms.
• All other elements will be in combination
with at least one other element (possibly
himself).
Molecules and Molecular Compounds
• A molecule is the smallest electrically
neutral unit of a substance that still has the
properties of that substance.
– Molecules are made up of two or more atoms
that act as a unit (usually nonmetals)
• These atoms may be from the same element
– Examples are ozone and the seven diatomic molecules
• These atoms may be from different elements.
– Examples are CO2 and H2O
Molecules can exist as single entities. The graphic below is showing you
that two molecules of hydrogen will react with one molecule of oxygen to
produce two molecules of water.
Properties of molecular compounds
• These compounds can be solids, liquids,
or gases
– Depends upon the forces of attraction
between the molecules (future unit)
• Molecular compounds tend to have
relatively low melting and boiling points.
• When dissolved in water, these
compounds rarely conduct electricity.
Ions and Ionic Compounds
• Ions are atoms or groups of atoms that have
a positive or negative charge.
– A cation is any atom or group of atoms that has
a positive charge.
• Metals will become cations by losing electrons.
– An anion is any atom or group of atoms that has
a negative charge.
• Nonmetals will become anions by gaining electrons.
• Compounds that are composed of cations
and anions are called ionic compounds
The graphic below is illustrating how an ionic crystal might appear. Where a
molecule can exist as a single entity, the ionic compound represents the
smallest ratio of ions in an ionic crystal. The crystal below represents NaCl.
Properties of Ionic Compounds
• High melting points (ionic bond very strong)
• Ionic compounds tend to be brittle
• Many ionic compounds dissolve in water
(a process that separates the ions)
• Solutions of ionic compounds are good
conductors of electricity (free-floating ions)
• Molten ionic compounds also conduct
• Solid ionic compounds do not conduct
electricity (no free-floating ions)
Characteristics of Molecular & Ionic Compounds
Characteristic
Representative
Unit
Type of
Elements
Physical State
Melting Point
Molecular Cpd
Ionic Compound
Molecule
Formula unit
Nonmetals
Metal &
nonmetal
Solid
Solid, liquid, or
gas
Low
(usually < 300°C)
High
(usually > 300°C)
Representing Chemical
Compounds
• A chemical formula shows the kinds and
numbers of atoms in the smallest
representative unit
– To represent an ionic compound, chemists
use a formula unit, which is the lowest wholenumber ratio of ions in the compound.
– A molecular formula shows the kinds and
numbers of atoms present in a molecule of a
molecular compound.
Three types of ions
• Monatomic cations
• Monatomic anions
• Polyatomic ions (memorize sheet)
Monatomic Cations
• These cations are formed when metals
lose electrons.
• These cations will have the same name as
the element.
• The metals in groups 1, 2, & 3 will always
have a certain charge.
– Group 1 metals all lose 1 electron to get a +1 charge.
– Group 2 metals all lose 2 electrons to get a +2 charge
– Group 3 metals all lose 3 electrons to get a +3 charge
Transition metal cations
• The metals in the transition metal region
and those metals at the bottom of groups
4 and 5 have several possibilities for
charges, depending upon conditions.
– In order to distinguish among the possibilities,
roman numerals are used.
– Fe2+ called iron(II); pronounced “iron two”
– Fe3+ called iron(III); pronounced “iron three”
– Three exceptions (“the chosen ones”)
• Cd and Zn always 2+; Ag always 1+
Monatomic Anions
• These anions are formed when nonmetals
gain electrons.
• These anions will change their name to an
–ide ending.
• The nonmetals in groups 5, 6, & 7 will
always have a certain charge
– Group 5 nonmetals all gain 3 electrons to get a 3- charge
– Group 6 nonmetals all gain 2 electrons to get a 2- charge
– Group 7 nonmetals all gain 1 electron to get a 1- charge
Revisit Blank Periodic Table
• We added the charges on the columns
– Group 1 “+1”, Group 2 “+2”, Group 3 “+3”
– Group 4 “+/-4”
– Group 5 “-3”, Group 6 “-2”, Group 7 “-1”
– Group 8 has zero charge
• The transition metals can have various
charges depending upon conditions. But
three of them have certain charges.
– Zn and Cd are always +2; Ag is always +1
– I call them the “chosen ones”
Revisit Concept Map (ovals)
• On the metal side, add an oval
– “metals lose electrons to become cations”
• On the nonmetal side, add an oval
– “nonmetals gain electrons to become anions”
Now….
• Download and print the “In Class
Worksheet”
• We did this worksheet as a group to
understand that
– Metals lose electrons to become cations
• The metals keep their names.
– Nonmetals gain electrons to become anions
• The nonmetals change their names to an –ide
ending.
Compounds
Ionic compounds
cations, anions
+ guy 1st, - guy 2nd
Balance charges by flipping
Binary ionic compounds
Cation, anion
Metal, nonmetal
+ guy 1st, - guy 2nd
Balance charges by flipping
Name ends in -ide
molecular cpds
Binary Ionic Compounds
Write each ion with
his charge. Flip
charges….the
charges help you
determine the
subscripts for the
formula.
Writing formulas from names:
Lithium sulfide Li+1S-2
Li2S
Chromium III iodide Cr+3I-1
Strontium nitride
Sr+2N-3
Tin IV sulfide Sn+4S-2
CrI3
Sr3N2
Sn2S4
SnS2
Binary Ionic compounds, cont
Writing names from formulas:
CaBr2 calcium bromide
(calcium from group 2)
CuI copper I iodide
CuI2 copper II iodide
(copper is a transition metal; not chosen)
BaO barium oxide
FeO iron II oxide
First, name each ion. Then
check to see if the cation comes
from groups 1, 2, or 3 of the
periodic table or is a chosen one.
If so, the naming is complete. If
the cation comes from the
transition metal region or the
bottom of groups 4 or 5, then
you must determine the charge
of that cation in order to give it a
roman numeral.
(barium from group 2, iron is a transition metal; not chosen)
How to determine the roman numeral?
You need to look at the anion.
Ex. 1
CuI
The iodide has a -1 charge. Since there is only one iodide, the copper
must have a +1 charge for the compound to have no charge. Hence, roman
numeral I.
Ex. 2
CuI2
The iodide has a -1 charge. There are two iodides, so a total of -2.
since there is only one copper, the copper must have a +2 charge for the
compound to have no charge. Hence, roman numeral II.
Polyatomic Ions
• Groups of atoms that have a charge
• Fourteen polyatomic ions are listed on the
memorize sheet….learn them
• Notice that those polyatomic ions that
have oxygen at the end of the formula
have a name that ends in –ite or –ate.
• Also notice that there are four pairs of
polyatomic ions….the –ate has more
oxygens than the –ite.
Let’s continue the “compound tree”
Ternary Ionic Compounds
• Have more than two elements
• Must have at least one polyatomic ion
• Cation, anion
• + guy 1st, - guy 2nd
• Sometimes use parentheses
• Name most likely ends in –ate or -ite
Ternary Ionic Compounds
Writing formulas from names:
(Follow the same pattern used for binary ionic compounds…sometimes you will
need parentheses.)
Rubidium carbonate Rb+1CO3-2
Rb2CO3
Aluminum sulfite
Al+3SO3-2
Al2(SO4)3
Cesium phosphite
Cs+1PO3-3
Cs3PO3
Manganese II cyanide Mn+2CN-1 Mn(CN)2
Ternary Ionic compounds, cont
• Writing names from formulas:
(same as before…name the ions…if cation is not in groups 1, 2, or 3 or is not a
chosen one, you will need to determine a charge in order to assign a roman
numeral)
Ca(C2H3O2)2
calcium acetate
SnCO3
tin II carbonate
(NH4)3P
ammonium phosphide
Let’s continue the compound tree:
Molecular compounds
•
•
•
•
Binary molecular compounds
Means only two nonmetals
No charges, no flipping
1st guy has his element name, 2nd guy has his
–ide name
• Use the prefixes in the name
– Mono, di, tri, tetra, penta, hexa, hepta, octa, nona, deca
– 1, 2, 3, 4,
5,
6,
7,
8,
9,
10
Two naming exceptions
1. When there is only one of the first
element in a molecular compound, do not
use the prefix “mono”.
2. When a prefix with an “a” or “o” comes up
next to oxygen or oxide, drop the “a” or
“o”.
Binary Molecular compounds
Writing formulas from words:
Dicarbon hexahydride 2 carbons, 6 hydrogens
C2H6
Carbon dioxide 1 cargon, 2 oxygens
CO2
Trinitrogen heptoxide 3 nitrogens, 7 oxygens
N3O7
Binary Molecular compounds
Writing names from formulas:
CO carbon monoxide
(there is only one carbon….do not use mono for the first guy; there is only one
oxygen….you must use mono for the 2nd guy)
P2O5 diphosphorus pentoxide
(when a prefix with an “a” or “o” comes up next to oxygen or oxide, drop that “a”
or “o”)
N4S6 tetranitrogen hexasulfide
Acids
• Acids are compounds that have a
hydrogen ion in the beginning and some
anion at the end.
• The name of the acid depends upon the
anion.
• The three anion endings are…..
-ide, -ate, and -ite
Acid naming table
Anion Ending Example
Acid Name
Example
-ide
Cl-, chloride
Hydro-(stem)-ic acid
Hydrochloric acid
-ate
SO4-2, sulfate
(stem)-ic acid
Sulfuric acid
-ite
PO3-3, phosphite
(stem)-ous acid
Phosphorous acid
Please note…
• When naming an acid containing sulfate or sulfite, you need to add an extra
syllable “ur”.
• When naming an acid containing phosphate or phosphite, you need to add
an extra syllable “or”.
Acids
Writing names from formulas…
HCl
(Cl is chloride….an –ide is a “hydro – ic acid”, so the
name is hydrochloric acid)
H2SO4 (SO4 is sulfate….an –ate is an “-ic acid”, so the name
is sulfuric acid….notice the extra syllable “ur”)
H3PO3
(PO3 is phosphite….an –ite is an “-ous acid”, so the
name is phophorous acid….notice the extra syllable “or”
Acids
Writing formulas from names
Hydrocyanic acid
H+1 CN-1
HCN
(a hydro-ic acid means cyanide. Check charges on both
the hydrogen and the cyanide….flip charges.)
Nitric acid
H+1 NO3-1
HNO3
(an –ic acid means nitrate. Check charges on both the
hydrogen and the nitrate….flip charges.)
Sulfurous acid H+1 SO3-2
H2SO3
(an –ous acid means sulfite. Check charges on both the
hydrogen and the sulfite….flip charges)