Transcript Naming Compounds and Writing Formulas

Naming Compounds and
Writing Formulas
Ms Titolo – Chemistry 112
Unit VI
Review of terms:
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Cation: positive ion formed by losing
electrons.
Anion: negative ion formed by gaining
electrons
Monatomic Ion: cation or anion formed
from a single atom. Ex: Mg+2, Na+1
Polyatomic Ion: group of atoms that
form a single charged unit. Ex: CO3-2
Review of terms continued:
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Ionic Bonds: bonds formed by the
attraction of oppositely charged ions
created by the transfer of electrons.
Ionic bonds are formed between a
metal and non-metal or a bond
involving a polyatomic ion.
Covalent bonds: bonds formed by the
sharing of electrons between two nonmetals or a metalloid.
Types of Compounds
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Ionic Compound: chemical compound
composed of cations and anions
combined so that the total positive and
negative charges are equal. Occurs
between a metal and non-metal (could
be a metalloid) or includes a polyatomic
ion.
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Covalent Compound: formed by the
sharing of electrons and does not
involve ions. Occurs between two nonmetals or could be a metalloid
Valence electrons and
Oxidation Numbers reviewed:
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Valence electrons: electrons in the
outermost energy level.
Oxidation number is the charge formed
when an ion is formed by losing or
gaining electrons.
Nomenclature (naming) of
ions:
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To name a monatomic cation you
simply write the elements name and
add the word ion. Ex: Mg+2 is a
magnesium ion.
To name a monatomic anion you take
the elements name, drop the ending
and add ide, then add the word ion. Ex:
Cl-1 is a Chloride ion.
Oxidation Numbers Cont….
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Oxidation numbers for transition metals
cannot be determined by looking at the
periodic table. Transition elements form
ions in more than one way….can have
more than one oxidation number.
Only three transition elements have
consistent oxidation numbers that you
will need to memorize: Zn+2, Ag+, and
Cd+2
Transition elements:
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To show the oxidation numbers on
transition elements
In addition to transition elements tin
and lead…under the metalloid stairstep,
need a roman numeral too.
Ex: Cu+ = Copper (I) ion, Cu+2 =
Copper (II) ion
Practice Ion Naming:
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Take a few minutes and look at the
back of page 2 in your handout and fill
in the chart at the top right of the
page…where it asks for the symbol,
formula and oxidation number (charge)
for the following…when you are finished
we will check your answers.
Naming Binary Ionic
Compounds:
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Binary ionic compound is any ionic
compound that includes only two
elements.
Nomenclature (naming)
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Combine the names of the two ions.
Always write the cation first and then the
anion.
When writing the anion, don’t forget to
drop the ending and add -ide.
Naming continued…
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Ex. 1 – A name for the combination of
Cs+ and Cl- …it would be Cesium Chloride
Ex. 2 – A name for the combination of
Ba+2 and O-2… it would be Barium Oxide
Writing Ionic Formulas:
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An ionic compound must be combined
where the positive and negative
charges are equal, and should be in the
lowest possible whole number ratio.
Examples:
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Na+1 combines with Cl-1 When these two
ions combine their charges cancel each
other out and are in a 1:1 ratio so the
formula is NaCl and the name is Sodium
Chloride
Ionic Formulas Examples
Cont….
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Ba+2 combines with O-2 When these two
ions combine they also have charges that
cancel each other out. They are a 1:1
ratio. The formula would be BaO and the
name Barium Oxide.
Ionic Formulas Examples
Cont….
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Mn+4 combines with O-2. These two ions have
charges that do not cancel out. We must find
the least common multiple of the number of
ions needed to allow the charges to cancel
out….You would need 1 Mn+4 to make a + 4
charge and 2 O-2 to make a –4 charge.
Therefore the formula is MnO2 and would be
named Manganese IV Oxide (the roman
numeral is needed to show the charge since
Manganese is a transition metal)
Formulas cont…
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Superscripts are the charges related to
the ion…only used when writing the
formula of an ion….not in a compound.
Subscripts are used in formulas to show
how many of each element is needed to
have a neutral compound. If there is
no subscript then it is one.
Subscripts cont…
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If you need to add a subscript to a
polyatomic ion (need more than one of
them) put parenthesis around the ion
and the subscript outside. Pb (NO3)4
Practice Ionic Naming and
Formulas:
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DO NOT WRITE THIS!!
Go the back of the first page of your
handout and try to write the formulas
and names of the compounds in the
sections Ionic compounds – write
formulas and Write the names.