Chapter 9 - hwchemistry

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Transcript Chapter 9 - hwchemistry

Chemical Names
& Formulas
Chapter 9
Ionic vs. Covalent
• Ionic bonds form between a metal cation
and a non-metal anion.
• There is a full transfer of electrons.
• A covalent (molecular) bond occurs
between two non-metals.
• Electrons are shared.
Ion – an atom or group of atoms with a charge
Cation – Ion with a positive charge
Anion – Ion with a negative charge
Monatomic ion – consist of a single atom
Polyatomic ion – consists of more than one type
of atom
• Elements in group 1, 2, and 3 lose electrons and
form cations.
• Why is sodium + 1 and magnesium is + 2?
(hint: drawing a diagram may help)
• Atoms try to achieve noble gas configuration
with their electrons.
• Cations have the same name as the element from
which they form
• Elements in group 15, 16, & 17 gain electrons to
form anions
• How many electrons will chlorine gain?
what will its charge be?
• Monatomic anions have the ending -ide
• The remaining elements in group 4 & 14
don’t normally form ions. Why?
Ions of Transition
• Transition metal cations may have more than one possible
• Iron for example can have a +2 or a +3 oxidation state.
• A roman numeral in parantheses shows the oxidation state
of the metal.
– e.g. Iron (III), Iron (II)
• A few transition metals have only one
oxidation state (Ag+, Cd2+, Zn2+) and
do not need a Roman Numeral.
• Can you find any other transition
metals that have only one oxidation
Writing Formulas
• Formulas need to have an overall charge of
• Write the symbol of the cation first then the
anion. Then, add whatever subscripts are
needed to balance the charges.
 Example:
Potassium chloride is composed of
K+ and Cl The formula is KCl
• The formula for lithium oxide is Li2O
• Each lithium has one positive charge,
so two lithium atoms are needed to
balance the –2 charge on oxygen.
• The formula for aluminum oxide is
• How do we come up with this formula?
The Crisscross Method
If the charges do not already add to zero,
the numerical value of the charge can be
crossed down to become the subscript of the
other ion.
Al3+ O2-
Polyatomic Atoms
Composed of more than one atom,
most of these ions end in –ite or
Formulas With
• Write the symbols for the cation followed
by the formula for the polyatomic anion,
and balance the charges.
• If you need more than one polyatomic ion,
(parentheses are necessary)
• Calcium nitrate is written Ca(NO3) 2
Write the correct formula for the following:
- Lithium fluoride
- Magnesium chloride
- Aluminum sulfide
- Calcium phosphate
- Potassium chlorite
Things to keep in
• There are three common polyatomic ions that
end in –ide
• Hydroxide
• Peroxide
• Cyanide
• You may run into 3 names together, e.g.
sodium hydrogen carbonate.
Naming Molecular Compounds
• Molecular compounds are covalently bonded and are
composed of two non-metals.
• What are the names for CO2 and CO?
– Carbon dioxide & carbon monoxide.
• Where do we find each of these gases?
• Prefixes tell us how many atoms of an element are present
in each molecule of a compound.
1 2
Mono Di Tri Tetra Penta Hexa Hepta
Octa Nona Deca
• Omit the prefix mono- when the formula contains only
one atom of the first element in the name.
• The ending of the second element is –ide
• The vowel at the end of a prefix is dropped if the name of
the elements begins with a vowel.
Writing Formulas for
Molecular Compounds
• The prefix tells you the subscript of each
element in the formula.
• Silicon carbide has no prefixes and has the
formula SiC.
• Dinitrogen tetroxide is N204
• An acid contains one or more hydrogen
atoms and produces H+ ions when dissolved
in water.
Formic Acid
Hydrofluoric Acid
Naming Acids
• Formulas are generally in the form
HnX, where X is an anion.
• The name system depends on the
name of the anion, suffix.
When the anion ends in –ide, the acid name
begins with hydro – and ends in – ic (followed by
the word acid)
ex. HCl = hydrochloric acid
When the anion ends in –ite, the acid name ends
in – ous (followed by the word acid)
ex. H2S03 = sulfurous acid.
When the anion ends in –ate, the acid name ends
in – ic (followed by the word acid)
ex. HN03 = nitric acid.
Naming Bases
• Bases are named the same way as
other ionic compounds.
Ex. NaOH = sodium hydroxide
Al(OH)3 = aluminum hydroxide