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.
IONS
•
•
•
•
•
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
CATIONS
• 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
ANIONS
• 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
Metals
• Transition metal cations may have more than one possible
charge.
• 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)
…continued
• 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
state?
Writing Formulas
• Formulas need to have an overall charge of
zero.
• 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
…CONTINUED
• 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
Al2O3
• 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
-ate
Formulas With
Polyatomics
• 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
PRACTICE
Write the correct formula for the following:
- Lithium fluoride
- Magnesium chloride
- Aluminum sulfide
- Calcium phosphate
- Potassium chlorite
Things to keep in
mind…
• 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
• Prefixes tell us how many atoms of an element are present
in each molecule of a compound.
1 2
3
4
5
6
7
Mono Di Tri Tetra Penta Hexa Hepta
8
9
10
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
ACID
• 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.
RULES
1)
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
2)
When the anion ends in –ite, the acid name ends
in – ous (followed by the word acid)
ex. H2S03 = sulfurous acid.
3)
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