PRE-AP CHEMISTRY
CHAPTER 4
CHEMICAL NAMES AND FORMULAS
Molecule - neutral group of atoms that acts as a unit (electrons are shared)
diatomic molecule –consists of two atoms of the same element (O2, oxygen)
triatomic molecule- consists of three atoms of the same element (O3, ozone)
Molecular compound-usually composed of 2 or more nonmetals
-often gases or liquids at room temperature
-low melting & boiling points
Ions- atoms or groups of atoms that have a positive or negative charge. Ions are formed when
one or more electrons are lost or gained.
Cation- positively charged ion
-electrons were lost
-metals tend to form cations
-name of monatomic cation is the same as the element
Examples:
Na  Na+ + eCa  Ca2+ + 2eFe  Fe3+ + 3eAnion- negatively charged anion
-electrons were gained
-nonmetals tend to form anions
-name of monatomic anion ends in –ide
Examples:
Cl + e-  ClO + 2e-  O2N + 3e-  N3“We think positively about cats (cations) and negatively about ants (anions)!”
Ionic compound-composed of positive and negative ions arranged in a 3-D pattern
-electrically neutral
-usually metal & nonmetal
-mostly solids at room temperature
Chemical formula- shows the number and kinds of atoms in the smallest representative unit of the
substance.
Molecular formula- chemical formula written for a molecule
Formula unit- chemical formula written for an ionic compound.
-lowest whole-number ratio of ions in the compound
Monatomic Ions
The charge of a monatomic ion can often be determined by the element’s position on the periodic
table:
Group 1A: 1+ Ex. Na+
Group 2A: 2+ Ex. Ca2+
Group 3A: 3+ Ex. Al3+
Group 5A: 3- Ex. N3Group 6A: 2- Ex. O2Group 7A: 1- Ex. F-
Elements in Group 0 (8) do not form ions. Elements in Group 4 rarely form ions. They tend to
react by sharing electrons instead of transferring electrons.
Transition Metal ions:
Most transition metals form more than one ion. They are stable losing varying numbers of
electrons. The possible charges must be memorized.
Exceptions: Zinc and Cadmium will always be 2+ and Silver will always be 1+.
Stock names use Roman numerals to represent the charge. For example, iron(II) is Fe2+.
Classic names use the suffix –ous or –ic. The ion with the –ous ending always has the lower
charge. The ferrous ion is Fe2+ and the ferric ion is Fe3+.
The mercury(I) ion is unique. It only exists in pairs of mercury(I) ions (like Siamese twins). Its
symbol is Hg22+.
Sample ion quiz:
Sodium __Na+__
Selenide __Se2-__
chromous __Cr3+___
tin(IV)
___Sn4+__
Polyatomic Ions
-tightly bound groups of atoms that behave as a unit and carry a charge
-atoms are bound together by shared electrons
The only positively charged polyatomic ion that we need to memorize is ammonium, NH4+.
Ions that end in –ite or –ate contain oxygen. In a series such as sulfate and sulfite, the –ite ending
has one less oxygen than the –ate ending.
ClO4ClO3ClO2ClO-
perchlorate
chlorate
chlorite
hypochlorite
CO32carbonate
HCO31- hydrogen carbonate or bicarbonate
PO33- phosphite
PO43- phosphate
HPO42- hydrogen phosphate
H2PO41- dihydrogen phosphate
Law of Definite Proportions- In all samples of any chemical compound, the elements are always
combined in the same proportion by mass. Ex. Water is always 88.9%O and 11.1%H by mass
Law of Multiple Proportions- Whenever two elements form more than one compound, the
different masses of one element that combine with the same mass of the other element are in the
ratio of small whole numbers.
Ex. N2O
28gN : 16gO
1.75 : 1
NO
14gN : 16gO
0.875 :1
1.75 : 0.875 = 2:1
Writing Formulas
Binary compounds- 2 elements
Binary ionic compounds- 1 metal + 1 nonmetal
Binary molecular compounds- 2 nonmetals
When writing the formula for an ionic compound, the charges of the ions must cancel out to give
the compound a neutral charge.
Ex. Sodium sulfide
magnesium nitride
Na+
S2Mg2+
N3Na2S
Mg3N2
Practice: strontium selenide
Sr2+ Se2SrSe
Cesium sulfate
Cs+ SO42Cs2SO4
rubidium iodide
Rb+ IRbI
potassium chromate
K+ CrO42K2CrO4
When naming ionic compounds containing a transition metal, don’t forget to include the Roman
numeral for the charge.
Ex. FeCl2 iron(II) chloride
FeCl3 iron(III) chloride
Practice: PbCl4
lead(IV) chloride
or plumbic chloride
MnF3
manganese(III) fluoride
or manganic fluoride
Hg2Cl2
mercury(I) chloride
or mercurous chloride
When writing formulas including polyatomic ions, use parenthesis around multiple polyatomic
ions.
Ex. Iron(III) sulfate
Fe2(SO4)3
Ammonium carbonate (NH4)2CO3
Practice:
Strontium hydroxide
Sr2+ OHSr(OH)2
calcium nitrate
Ca2+ NO3Ca(NO3)2
When naming binary molecular compounds, prefixes are used to tell how many of each atom is in
the formula.
Ex. carbon dioxide CO2
dinitrogen tetroxide N2O4
The prefix mono- is never used with the first element. The list of prefixes is found on page 159.
Learn them!!!!
Practice: CBr4
ICl3
P2O5
carbon tetrabromide
iodine trichloride
diphosphorus pentoxide
Sulfur hexafluoride
SF6
tetraarsenic hexaoxide
As4O6
Mixed Practice:
Rb2Se
rubidium selenide
Cu(OH)2
copper(II) hydroxide or cupric hydroxide
NaClO3
sodium chlorate
NaH2PO4
sodium dihydrogen phosphate
CO
carbon monoxide
MgCr2O7
magnesium dichromate
CoCl3
cobalt(III) chloride or cobaltic chloride
P4O10
tetraphosphorus decoxide
Barium hydrogen carbonate
Ba2+ HCO3Ba(HCO3)2
calcium hypochlorite
Ca2+ ClOCa(ClO)2
silver cyanide
Ag+ CNAgCN
Tin(IV) oxide
Sn4+ O2SnO2
lithium hydride
Li+ HLiH
cesium sulfite
Cs+ SO32Cs2SO3
dinitrogen tetrafluoride
N2F4
Base- compound that produces OH- in water solution
Acid-compound that produces H+ in water solution
NAMING ACIDS:
Anion ending
-ide
-ate
-ite
Ex.
acid prefix
hydro-
acid suffix
-ic
acid
-ic
acid
-ous
acid
HNO3
nitrate nitric acid
H2SO4 sulfate  sulfuric acid
H2SO3
sulfite  sulfurous acid
H2CrO4 chromate  chromic acid
HClO4 perchlorate  perchloric acid
HCl chloride  hydrochloric acid
HCN cyanide  hydrocyanic acid
Practice:
HClO  hypochlorite ion  hypochlorous acid
HNO2  nitrite ion  nitrous acid
HBr  bromide ion  hydrobromic acid
H3PO4  phosphate ion  phosphoric acid
Chlorous acid  chlorite ion (ClO2-)  HClO2
Carbonic acid  carbonate ion (CO32-)  H2CO3
Oxalic acid  oxalate ion (C2O42-)  H2C2O4
Hydrofluoric acid  fluoride ion (F-)  HF