I. Naming Ionic Compounds
A. Ionic compounds are formed by the strong
attraction between oppositely charged
particles, cations (positive ions) and anions
(negative ions)
B. Both ions are important to the compound’s
structure, so both ions are included in the
name.
C. The names of ionic compounds consist of
the names of the ions that make up the
compounds.
D. In many cases, the name of the cation is just like the
name of its element.
E. Where an atom is located can be used as a tool for
figuring out what ions are formed by different
elements:
i. Atoms of Group 1: form ions with a +1 charge
ii. Atoms of Group 2: form ions with a +2 charge
iii. Atoms of Group 13: form ions with a +3 charge
iv. Atoms of Group 15: form ions with a -3 charge
v. Atoms of Group 16: form ions with a -2 charge
vi. Atoms of Group 17: form ions with a -1 charge
vii.Atoms of Group 18: do not form ions because they
have a full outer energy level
F. Names of anions are altered names of
elements; the difference is in the ending.
i. For anions, drop the ending and add –ide.
G.An ionic compound must have a total charge of
zero.
i. Example: Calcium fluoride: Calcium has a +2
charge and fluoride has a -1 charge. For
calcium fluoride to have a total charge of
zero, there must be 2 fluoride ions for every
calcium ion. So, the formula is CaF2.
H.Transition metals must show their charge when
they form ions.
i. Example: FeO and Fe2O3 would both be
named iron oxide by the above rules. They
are not the same compound, so their
compound names are different. The charge
of the iron cation in Fe2O3 is different from
the charge of the iron cation in FeO.
Fe2O3, Iron (III) oxide
is a component of
rust.
FeO, Iron (II) oxide
is a black powdery
substance.
1. When this happens, the cation name MUST be
followed by a Roman numeral in parentheses.
2. The roman numeral shows the cation’s charge.
3. Fe2O3 is made of Fe3+ ions, so it is named iron
(III) oxide. How do you know the charge on iron
is +3? Each oxygen ion has a -2 charge, and
there are 3 of them. -2 times 3 is -6, so the
charge on iron has to be +6. There are 2 iron
ions, so 6/2 = 3.
4. FeO is made of Fe2+ ions, so it is named Iron (II)
Oxide. How do you know the charge on iron is
+2? Each oxygen ion has a -2 charge, and there
is only 1 of them. The charge on Fe has to be +2
because there is only one of them.
I. Once you have determined a chemical formula,
always check the formula to see if it makes a
neutral compound. Compounds are ALWAYS
neutral.
II. Writing Ionic Compounds: Write the chemical formula
for aluminum fluoride.
A. Steps used to write formulas for Ionic Compounds:
i. Write the symbols and charges for the ions with
the cation first.
Al+3 F-1
ii. Write the Lewis structure for each element and
show the transfer of electrons or use the puzzle
pieces.
Al
F
F
F
iii. Write the chemical formula. Show with
subscripts the number of each ion needed to
make a neutral compound.
AlF3
B. Practice: Write the formulas for the following
ionic compounds:
i. Lithium oxide
ii. Beryllium chloride
iii. Titanium (III) nitride
iv. Rubidium Oxide
Naming Covalent Compounds
I.
Numerical prefixes are used to name covalent compounds
A.
i.
Numerical prefixes tell how many atoms of
each element are in the molecule.
Rules:
B.
i.
If there is only one atom of the first element,
it doesn’t get a prefix.
1.
Example: CO is named Carbon Monoxide
ii.
iii.
The element that is farther to the right in the
periodic table is second and ends in –ide.
1. Example: BF3 is named Boron Trifluoride
Sometimes, the a in prefixes is dropped if it is
next to a vowel.
i. Example: N2O4 is named Dinitrogen
Tetroxide instead of Dinitrogen Tetraoxide.