BAN Dihydrogen monoxide!
Making Molecules
Chemical Nomenclature (ionic compounds)
CONVENTIONS
Scientists have agreed on a set of rules that govern the
naming and formulation of compounds. It is universal! The
following pages are a programmed approach to the problem
of obtaining either the formula or name of a chemical
compound.
a) The compound will be formed by combining a metal and a
non-metal. The metal portion will always appear first in the
name and formula.
b) The total number of electrons lost by the metal atom(s)
must equal the total number of electrons gained by the nonmetal atom(s). (The charge left after an atom gains or loses
electrons is called its valence.)
c) The symbols for the elements consist of one or more
letters. The FIRST is always a CAPITAL LETTER, and the
SECOND, if used is always a LOWER CASE LETTER.
d) The charge of the ion is always written as a superscript,
above and to the right of the symbol for the element.
i.e. Na+1 , F-1, Ca+2
e) The number of atoms of an element in a compound is
written as a SUBSCRIPT, below and to the right of the symbol
for the element. (ones, “1” are not used, but are
“understood”)
i.e. H2 or O2
The formula of a compound is P2O.
In this material, the atoms present are
phosphorous and oxygen. 2 atoms of
phosphorous combine with 3 atoms of oxygen to
form a molecule of the compound.
What atoms are present in the following
compounds? How many atoms of each are
involved?
H2O
AlF3
SnH4
K2S
PbO
CO
K3PO4
AgI
f) Brackets are sometimes used to contain groups of atoms (called polyatomic ions).
If a number appears to the right and below (subscript) the bracket, the subscript is
ONLY multiplied by the atoms appearing inside the brackets.
i.e. Al(NO3)3
This compound contains the following atoms:
1 x Al = 1 atom of aluminum
3 x 1 x N = 3 atoms of nitrogen
3 x 3 x O = 9 atoms of oxygen
Which elements are present in the following compounds and how many atoms are
there of each?
Al2(SO4)3
Mg(OH)2
(NH4)3PO4
Sb2(Cr2O7)5
Mn(C2H3O2)4
g) The second word of any chemical name ALWAYS starts with a “lower case” letter.
The first word of any chemical name can start with a lower case or capital letter,
depending on the context.
i.e. Sodium chloride
or
sodium chloride
How to determine the chemical formula of an ionic
compound ?
A chemical formula includes the symbol and the
number of each element in the compound.
Example:
The chemical formula H2O represents a compound
with :
_____ hydrogen atoms and
_____ oxygen atoms.
How do we determine the number of each element in a
compound?!
How do we determine the number of each
element in a compound?!
1st method: Transfer of electrons
Draw a Lewis diagram of each element found in the
compound
Draw arrows to show the exchange of electrons
Add atoms and their exchange of electrons until all of
the atoms are stable.
Ex 1: sodium and sulfur
Ex 2: calcium and fluorine
Ex 3: beryllium and phosphorous
2nd Method: Criss-cross
Write each symbol of each atom with the ionic charge
just above it.
Cross the ionic charges to use them as subscripts.
Do not write number “1” at any point
Divide the subscripts by the same number when
possible (like when you reduce a fraction).
Practice:
Elements
Chemical
Formula
Elements
Li and F
Ca and Br
Na and P
Mg and O
Ca and Cl
Na and S
Be and O
Be and C
K and S
Ca and I
Mg and Br
Mg and Si
Chemical
Formula
Binary Compounds
Binary compounds are those that contain only TWO elements.
FROM FORMULA TO NAME
RULE 1: Binary Ionic Compounds:
1. Name the first element in the compound.
2. Name the second element in the compound. You must
change the ending of the name to IDE.
i.e. AlBr3
PRACTICE
Li2O
CaCl2
KI
AgBr
FROM NAME TO FORMULA
Remember: Binary compounds are those that contain only TWO elements.
METHOD
1. Put down the symbol for the metal and non-metal
2. Place the charge as superscripts beside the appropriate element
3. Criss-cross the charges (write them now as subscripts)
4. Drop the signs (+ve and -ve)
5. Remove the common factors (usually)
6. Forget about the “1’s”
i.e. Sodium oxide
Magnesium sulfide
PRACTICE
Hydrogen iodide
Aluminum bromide
Zinc nitride
Chromium oxide
Barium sulfide
Potassium fluoride
Calcium chloride
Nickel oxide
Silicon carbide
Silver sulfide
RULE 2: For compounds with a metal that has MULTIPLE VALENCES
Some metals, such as antimony and copper, have more than one
possible POSITIVE charge.
In a compound, the metal can have only one of the charges listed for
that metal.
The method we will use to designate the valence of these metals
CANNOT be used for elements with only one valence!
FROM NAME TO FORMULA
Preferred (IUPAC) Method
Method: *The roman numeral states the valence of the metal in the compound.
*Follow the rules for binary compounds BUT use the valence designated by the
roman numeral for the metal.
Mercury (I) oxide
tin (IV) sulfide
PRACTICE
Iron (III) fluoride
Antimony (v) sulfide
Sulfur (VI) oxide
Arsenic (III) Hydride
Phosphorous (v) chloride
Lead (II) oxide
Manganese (IV) carbide
Nitrogen (III) hydride
Copper (I) iodide
Mercury (II) carbide
RULE 2: For compounds with a metal that has MULTIPLE
VALENCES
FROM FORMULA TO NAME
If the metal portion of a compound has a multiple valence you must
obtain the TRUE valence from the formula.
1. Criss-cross the subscripts, and write them now as charges
(superscripts) .
*** Remember that the first element (the metal) has a positive
valence, while the second element (the non-metal) has a negative
valence***
2. Check that both the metal and non-metal have the correct valence,
and that no common factor has been eliminated.
3. First, name the metal, then use the roman numeral system to state
the metal valence in brackets, Thirdly, name the non metal, changing
the ending to ide.
i.e. CuCl
SnCl4
Check your answers in my binder!