monday november 12, 2012 (ws - building and naming ionic compounds)
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MondayNovember 12, 2012
(WS - Building and Naming Ionic Compounds)
Bell RingerMonday, 11-12-12
Write the formulas for the chemical compounds that are formed when the
following atoms bond:sodium and
chlorineNaCl
magnesium and bromine
MgBr2
calcium and oxygen CaO
aluminum and sulfur
Al2S3
Announcements
Assignment Currently Open
Summative or Formative? Date Issued Date Due Date Into
GradeSpeed Final Day
QUIZ 9 S6 10/26 10/26 11/16
QUIZ 10 S7 11/2 11/2 11/16
WS – Covalent Bonding F14 11/7 11/16 11/16
QUIZ 11 S1 11/9 11/9 11/30
Chemical Compound Formation and Naming
A chemical formula indicates
the types of atoms and relative
number of each type of atom in a
chemical compound.
Chemical Formulas
Chemical FormulasFor an ionic compound, the chemical
formula reveals the ratio of ions of each element contained in the ionic matrix.
Al2O3In the ionic compound aluminum oxide, there are 2 ions of aluminum for every
three ions of oxygen in the ionic matrix.
Monoatomic Ions•Ions are created when a neutral atom
loses or gains electrons in the process of becoming stable.
•The atom no longer has equal numbers of protons (+) and electrons (-).
•Monoatomic ions (meaning “one atom”) are ions formed from a single atom.
• H+ Ca2+ Cl- O2-
Polyatomic Ions•Polyatomic ions (meaning
“more than one atom”) are ions formed from multiple atoms
bonded into a group.
• NH4+ Hg2
2+ OH- SO42-
• Notice that the number 1 is not shown.
Chemical FormulasFor an ionic compound made with one or more
polyatomic ions, the chemical formula still reveals the ratio of ions, whether they are monoatomic
ions or polyatomic ions.
Al2(SO4)3In the ionic compound aluminum sulfate, there are 2 ions of aluminum for every three ions of sulfate in the ionic matrix.
Cations and Anions• When atoms lose electrons, they now
have more protons (+) than electrons (-), and take on the + charge of the extra protons. Positively charged ions are
called “cations.”
•K+
•NH4+
•Br-
•OH-
•When atoms gain electrons, they now have fewer protons (+) than electrons
(-), and take on the - charge of the extra electrons. Negatively charged
ions are called “anions.”
Oxidation NumbersOxidation numbers (the
green numbers above the main-block groups on the larger Periodic Table on the right) indicate the
charge on that atom’s ion after it has lost or gained electrons in the process of
becoming stable.
Na+
Mg2+
Al3+
C4+/-
Mg2+
N3-
O2-
F-
Oxidation NumbersOxidation numbers can be used to determine the ratio in which atoms
will bond to one another when forming chemical compounds.
This procedure is illustrated on the next slide.
“Crossing” oxidation numbers is a method of balancing the
charges between ions in an ionic compound.
For example:If an aluminum ion is bonding
with an oxygen ion:
Al3+ + O2-
Al2O3
Crossing Oxidation Numbers
Notice that you do not cross the +
and – charge signs, only the numbers
of the charges.
It is also important to remember that the positively-charged cation is always listed first in the chemical formula, followed by the negatively-
charged anion.
Crossing Oxidation Numbers
Therefore: Na+Cl-
Never: Cl-Na+
Oxidation NumbersIn general, follow this system for determining an
elements oxidation number:
Group 1 = 1+ (+)Group 2 = 2+
Group 13 = 3+
Group 14 = 4+/-
Group 15 = 3-
Group 16 = 2-
Group 17 = 1- (-)Group 18 = 0
Since the d-block Transition Metals
(Groups 3-12) have variable
oxidation states, their oxidation
numbers will be listed as a Roman
numeral.
Ex) Fe (III) = Fe3+
Binary Ionic Compounds
Binary ionic compounds are compounds composed of two different elements.
In a binary ionic compound, the total numbers of positive and negative
charges must be equal.
ExampleMagnesium and bromine
combine to form magnesium bromide.
Mg2+ + Br- → MgBr2It takes 2 Br- anions, each with a 1- charge to balance Mg with
its 2+ charge!
Binary Ionic Compounds
Naming Monoatomic Ions
Monoatomic cations are identified simply by
the element’s
name.
Naming Monoatomic IonsWhen
monoatomic anions are
bonded into compounds, their names are changed
to end in –ide
Naming Polyatomic Ions
The names of polyatomic
ions are never
changed as they are
bonded into compounds.
ExampleNa + NO3 æ NaNO3
sodium + nitrate æ sodium nitrate
Polyatomic Ions
Handout: Reference Sheet -
Polyatomic Ions
WorksheetBuilding and Naming
Ionic Compounds
MgF2
NaCl GaI3
SrO
HNO3
AlI3
H2SO4
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