Unit 6: Ionic and Molecular Compounds
Part 1: Ionic Compound Formulas
Part 2: Naming Ionic Compounds
Part 3: Naming Molecular Compounds
Unit Synapsis
In this Unit we will explore Ionic and Molecular
compounds. We will begin by looking at how metals for positive
ions and non-metals or groups of non-metals form negative ions.
From there we will see how these ions can combine to form what are
called “Ionic Compounds” and then learn the rules for naming
those compounds. From there we will look at entirely different type
of compounds; molecular compounds (a.k.a. covalent compounds)
and how to name those compounds.
Part 1: Ionic Compound Formulas
This section corresponds to Pg. 210 to 221 in your textbook
Part 1: Ionic Compound Formulas / Objectives
“After this lesson I can…
• …identify the type of Ion a main group element will form.
• …define and identify polyatomic ions.
• …write the formula’s for Ionic compounds when presented with a
cation and an anion.
• …write the formula’s for Ionic compounds when presented with
an element and/or the name of a polyatomic ion
• ...recognize that transition metals form positive ions but that the
magnitude of the charge can vary.
• …identify the parent cation & parent anion in an ionic compound
Ion Formation in Main Group Elements
• An Ion is an element or group of elements that has a positive or
negative charge.
• The positive ions are called cations.
• Metals form Positive Ions
• The negative ions are called anions.
• Non-metals or groups of non-metals form negative ions
• Some elements always form a specific ion with a specific charge.
These elements are called main group elements, and they are the
elements in the “A” column on your periodic table (columns 1,2
13,14,15,16,17, and 18 using the alternative column numbering
system).
• Elements in Column 1A form +1 ions
• Elements in Column 2A form +2 ions
• Elements in Column 3A(13) form +3 ions
• Elements in Column 7A(17) form -1 ions
• Elements in Column 6A(16) form -2 ions
• Elements in Column 5A(15) form -3 ions
Examples of Main Group Ion Formation
• Sodium is in the first column and always forms: Na+
• Strontium is in the second column and always forms: Sr2+
• Arsenic is in the fifth column and always forms: As3• Oxygen is in the sixth column and always forms: O2• Bromine is in the seventh column and always forms: Br-
Periodic Table Showing Common Ionization States
Image Credit: http://chemistry.tutorcircle.com/inorganic-chemistry/oxidation-states.html
‐-Practice Problems‐Directions: Identify the charge on the elements below…
1) Al
2) P
3) Na
4) F
5) Ca
6) Li
7) Mg
8) O
9) N
10) Cl
Polyatomic Ions
• Positive ions are, with a very few exceptions, single metal atoms.
• Some negative ions are single non-metals atoms, but many are not.
• Many of the negative ions are called polyatomic ions, which are
molecules that have a negative charge.
• You do not have to memorize any polyatomic ions because they are
listed in your textbook and on the back of your periodic table.
• Here are a few examples:
• Carbonate: CO32• Nitrate: NO3-
• Phosphate: PO43• Chlorite ClO3-
Polyatomic Ions
Image Credit: http://www.fccj.us/PolyatomicIons/McMurrayTable302.html
Ionic Compounds
• Ionic Compounds form when a cation combines with an anion.
• This happens because positive charges attract negative charges, duh!
• One of the simplest and classic examples of an ionic compound is
table salt:
• NaCl (1 Na+ ion and 1 Cl- ion)
• Another simple example includes Sodium Fluoride, which they put
your toothpaste:
• NaF (1 Na+ ion and 1 F- ion)
• Ionic compounds do not always form in a 1:1 ratio though,
sometimes the ratio is 2:1, 1:2, 3:1,1:3, or several other variations.
• What does always happen is that the charges balance each other out.
There are never charges “left over”
Ionic Compounds Formation: The Criss Cross Method
• The easiest way to determine the chemical formula for an ionic
compound is to “criss cross” the charges on the two ions. Using this
method the positive ion gets a subscript of equal value (but without the
charge) to the negative ion’s charge and vice versa.
• If a polyatomic ion is involved and there is more than 1, parenthesis
will have to be used.
• Examples:
• Ba2+ & Cl- forms…
• BaCl2
• Al3+ & I- forms…
• AlI3
• Na+ & CO32- forms…
• Na2CO3
• Na+ & N3- forms…
• Na3N
• Ca2+ & PO43- forms…
• Ca3(PO4)2
‐-Practice Problems‐Directions: Write the formulas for the Ionic Compounds below given the
species below…
1) Al3+ & F2) Mg2+ & OH-
3) Na+ & I4) K+ & O25) Boron & Dichromate
6) Strontium & Nitrogen
7) Rubidium & Sulfate
8) Calcium & Cyanide
9) Beryllium & Phosphate
Ion Formation for Transition Metals
• The Transition metals are not apart of the main group.
• They make up the “B” columns on the periodic table (3 through 12 in
the alternative column numbering system)
• Unlike like main group elements, ion formation for transition metals
is not easily predicted. On top of that, most of the transition metals
have more than one ionization state. Iron for example forms +1, +2,
& +3 depending on what anion it is bonded too.
• Because they are metals, the most you can assume is that they will
form a positive ion.
• While you can’t predict what ion a transition metal will form just by
finding it on the periodic table, you should be able to determine
what the ion is if it’s bonded to an anion.
• Examples:
• In the compound FeCl3, the two parent ions are…
• Fe3+ & Cl• In the compound FeCO3, the two parent ions are…
• Fe2+ & CO32-
Steps For Identifying Parent Ions
1) Find the positive ion. 99 out of 100 times the positive ion will be a
metal and a single atom.
2) If the Metal is in columns 1,2, or 3, you should know what the
charge is.
3) If the metal is a transition metal, write it down but recognize you
will have to figure out the charge later.
4) Whatever is leftover must be the negative ion. It might be a single
non-metal atom or it might be a polyatomic ion. Using either the
periodic table or the list of polyatomic ions, determine; (1) what
the ion is, (2) it’s charge, and (3) how many of the ions are in the
compound.
5) If your positive ion is a transition metal, you should be able to
deduce it’s charge and the number of ions based on your
conclusion about the negative ion.
‐-Practice Problems‐Directions: Determine the Parent Ions in the following compounds. If there
is more than one cation or anion, write down the total number of ions as a
coefficient.
1) InF3
2) CoS
3) CuSO4
4) CuCl
5) Zn3(PO4)2
6) CrCl2
7) CrPO4
8) Ni3P2
9) Ti3(PO4)4
10) AgNO3
Part 1 Additional Resources
• YouTube Video explaining how to identify the parent Ions.
Part 2: Naming Ionic Compounds
This section corresponds to Pg. 218 to 224 in your textbook
Part 2: Naming Ionic Compounds / Objectives
“After this lesson I can…
• …explain some of the basic rules for naming ionic compounds
• …write the chemical formula for an ionic compound when given
it’s name
• …write the name for a ionic compound when given it’s formula.
Nomenclature Rules the First Name
• The naming of Ionic compounds follows a very specific set of rules.
1) There are two names in ionic compounds; A first name and a last
name. The first name is the name of the cation and the second
name is the name of the anion.
2) If the cation is from columns 1A,2A, or 3A(13) then the first name
is simply the element name.
• Examples:
• NaCl = “Sodium Chloride”
• CaCl2 = “Calcium Chloride”
• AlCl3 = “Aluminum Chloride”
3) If the cation is a transition metal then a roman numeral is used to
indicate the charge on the cation. There are some exceptions to
this mentioned at the end.
• Examples:
• FeCl2 = “Iron(II) Chloride”
• FeCl3 = “Iron(III) Chloride”
• TiCl2 = “Titanium(II) Chloride”
• TiCl4 = “Titanium(IV) Chloride”
Nomenclature Rules for the Last Name
4) If the anion is from columns 5A(15), 6A(16), or 7A(17) the last part
of the elements name is converted to “-ide”
• Examples:
• Na3P = “Sodium Phosphide”
• Na2O = “Sodium Oxide”
• NaBr = “Sodium Bromide”
5) If the anion is a polyatomic ion, the last part of the compounds
name is simply the name of the polyatomic ion.
• Examples:
• Na3PO4 = “Sodium Phosphate”
• Na2CO3 = “Sodium Carbonate”
• NaNO3 = “Sodium Nitrate”
6) Finally, a few transition metals have only one oxidations state and
so you do not include a roman numeral. These include Zinc
(always Zn2+), Silver (Always Ag+), and Cadmium (always Cd2+)
Some Final Notes on Naming Ionic Compounds
• Note that nothing is done to indicate the subscript (if there is one).
You are simply supposed to know what the subscripts are, based on
what you learned about ionic compounds in part 1.
• Examples:
• NaCl = Sodium Chloride
• Na2O = Sodium Oxide
• Na3P = Sodium Phosphide
• So if the first name is “sodium,” you don’t necessarily know how
many sodium ions are in the compound until you identify the charge
on the negative ion.
• This applies to Transition metals too, the roman numeral indicates
the charge and NOT the total number of ions.
• Examples:
• Cu3(PO4)2 = “Copper(II) Phosphate”
• CuS = “Copper(II) Sulfide”
• Cu2S = “Copper(I) Sulfide”
Ionic Compound Naming Example
Image Credit: https://www.texasgateway.org/resource/nomenclature-ionic-compounds
Ionic Compound Naming Example
Image Credit: https://www.texasgateway.org/resource/nomenclature-ionic-compounds
Ionic Compound Naming Example
Image Credit: http://study.com/academy/lesson/rules-for-naming-ionic-compounds.html
‐-Practice Problems‐Directions: Write the formula for the following ionic compounds
1) Lithium Phosphate
2) Barium Chlorate
3) Aluminum Cyanide
4) Copper(I) Sulfide
5) Potassium Iodide
6) Sodium Bicarbonate
7) Chromium(III) Sulfate
8) Nickle(II) Nitride
9) Magnesium Dichromate
10) Tin(IV) Oxide
‐-Practice Problems‐Directions: Give the Name for the following ionic compounds
1) InF3
2) CoS
3) CuSO4
4) CuCl
5) Zn3(PO4)2
6) CrCl2
7) CrPO4
8) Ni3P2
9) Ti3(PO4)4
10) AgNO3
Part 2 Additional Resources
• Crash Course Chemistry #11: “`How to Speak Chemistrian”
• Note: This video covers naming acids and naming molecular compounds.
Molecular compounds is discussed in Part 3 so it does not hurt to watch it but
naming acids will not be covered this year.
• Khan Academy: Names and Formulas for Ionic Compounds
• Note: All of the links directly underneath the video are also helpful
Part 3: Naming Molecular Compounds
This section corresponds to Pg. 251 to 252 in your textbook
Part 3: Naming Molecular Compounds / Objectives
“After this lesson I can…
• …recall the basic difference between ionic compounds and
molecular compounds.
• …explain some of the basic rules for naming molecular
compounds
• …write the name for a molecular compound with given a chemical
formula.
• …write the formula for a molecular compound when given it’s
name.
Molecular Compounds
• Ionic compounds are formed between metals and non-metals
• Covalent compounds are formed between non-metals and other nonmetals (sometimes semi-metals)
• Covalent compounds are also known as molecular compounds.
• Another big difference is that ionic compounds have very high
melting and boiling points compared to the M.P.’s and B.P.’s of
covalent compounds.
Naming Molecular Compounds Containing Just Two Elements
• Just like Ionic compounds, molecular compounds have a first and
last names.
• Just like Ionic compounds, the first name is the first element in the
compound.
• Unlike ionic compounds, the names of covalent compounds do change
based on the subscripts in the chemical formula.
1) First name/element rules:
• If there is only 1 it’s simply the element’s name.
• If there is more than 1, you need to use a prefix.
2) Second name/element rules:
• Always gets a prefix; even if there is only 1.
• Always changed to “-ide” at the end.
Prefixes for molecular compounds
• 1 atom = “mono”
• 2 atoms = “di”
• 3 atoms = “tri”
• 4 atoms = “tetra”
• 5 atoms = “penta”
• 6 atoms = “hexa”
• 7 atoms = “hepta”
• 8 atoms = “octa”
• 9 atoms = “nona”
• 10 atoms = “deca”
• You will not have to memorize these for the test. You can have them
written on the back of your periodic table.
Molecular Compounds Examples
• SiF4 = “Silicon tetraflouride”
• CO = “Carbon monoxide”
• S2O = “Disulfur monoxide”
• CO2 = “Carbon dioxide”
• PBr5 = “Phosphorus pentabromide”
• H2O = “Dihydrogen monoxide”
• P2Cl8 = “Diphosphorus octachloride”
‐-Practice Problems‐Directions: Write the formula for the following molecular compounds
1) Diphosphorus pentaoxide
2) Silicon Dioxide
3) Carbon tetrabromide
4) Dinitrogen monoxide
5) Sulfur dioxide
6) Phosphorus pentabromide
7) Iodine trichloride
8) Nitrogen triiodide
9) Dinitrogen trioxide
‐-Practice Problems‐Directions: Write the name for the following chemical formulas
1) CS2
2) OF2
3) PCl3
4) NF3
5) N2O5
6) SCl6
7) SO3
8) NO
9) P2F6
Naming Flow Chart
Image Credit: http://www.abitlikethis.com/ionic-and-covalent-compounds-worksheet-answers/
Naming Flow Chart #2