CHEMICAL COMPOUNDS
Topic 6
COMPOUNDS

What is a compound?
A group of 2 or more elements
 It takes on properties different than those of the
separate elements that compose it

IONIC AND MOLECULAR COMPOUNDS

Ionic Compounds


Molecular Compounds


Are formed when atoms give/take electrons
Are formed when atoms share electrons
We’ll look at Ionic Compounds first
IONIC COMPOUNDS
PROPERTIES OF IONIC COMPOUNDS
Formed from metals and non-metals
 Forms ions in solutions
 Conducts electricity
 Solid at room temperature

HOW IONIC COMPOUNDS ARE FORMED


Once an atom give up electrons, it becomes positive
Once an atom takes electrons, it becomes negative
Na
9p
Cl
11p
9 e-
11 e-
REMEMBER…


Positives and negatives attract
Once Na becomes Na+ and Cl becomes Cl- , they are
attracted to each other
Overall charge
Na+
9p
Cl11 p
8 e-
12 e-
+1
-1
CHEMICAL FORMULAS

Chemical formula – uses symbols and
numerals to represent the composition of a pure
substance.
Symbol for
the element
hydrogen
The small
number here
means 2
atoms of
hydrogen
H2O
Symbol for
the element
oxygen
No small number
here means 1
atom of oxygen
THEORY BEHIND CHEMICAL FORMULAS
CaCl2
1 ion Ca
each ion is +2
1 x (+2) = (+2)
(+2)
2 ions Cl
each atom is -1
2 x (-1) = (-2)
(-2)
Overall charge on the compound = 0
HOW TO WRITE CHEMICAL FORMULAS
WITHOUT ACTING IT OUT OR DOING MATH

If your periodic table has ion charges listed in the
corner, look at the ion charge for each element.
Ca+2
and
Cl-1
Ca Cl
To become…

Ca1Cl2  CaCl2
The superscript should be written as a positive or a
negative because the number it’s representing is a
number of atoms, not a charge anymore.
WRITING CHEMICAL FORMULAS
Example: What is the chemical formula of the product of calcium and chlorine?
Step
1.
2.
Write the symbol of the metal, then the
non-metal
Write the number of the charge of the
metal as a subscript after the non-metal
3.
Write the number of the charge of the
non-metal as a subscript after the metal
4.
Simplify to lowest terms if applicable.
Eliminate any 1s if applicable
Example
Ca Cl
CaCl2
Ca1Cl2
Final Answer: CaCl2
Note: The superscript shouldn’t be written as a positive or a negative
because the number it’s representing is a number of atoms, not a
charge anymore.
NAMING IONIC COMPOUNDS
1.
2.
The name includes both elements in the
compound, with the name of the metal first.
The non-metal element is second. Its ending is
changed to –ide.
Examples:
Calcium chloride (instead of Calcium chlorine)
Magnesium flouride (instead of magnesium
flourine)
Sodium iodide (instead of sodium iodine)
Zinc sulfide (instead of zinc sulfur)
POLYATOMIC IONS
Some ions form when certain atoms of elements
combine. These ions are called polyatomic ions.
(poly- means “many”).
 Polyatomic ions are a group of atoms acting as
one.
 They combine with metals in the same way that
a single atom does.

WRITING CHEMICAL FORMULAS WITH
POLYATOMIC IONS

Chemical formulas are written almost the same as
other ionic compounds.
Calcium and nitrate
 Ca+2 and NO3


CaNO3

Ca(NO3)2  why not just CaNO32?
Differences: Brackets must be written around
the polyatomic ion to identify that it is acting as
one atom
NAMING COMPOUNDS WITH POLYATOMIC
IONS

Naming with a polyatomic ion is very similar to
naming compounds between two elements


…but easier
Write the name of the metal, then the name of
the polyatomic ion.
 Do

NOT change the ending of the polyatomic ion
Examples:

Calcium carbonate, sodium nitrate
MULTIVALENT IONS

Some ions have the ability to give up different
amounts of electrons which means that they have
two possible charges.
Writing formulas with multivalent ions are done
just as they were with an ion with only one
charge.
 Titanium + Oxygen = Ti2O3

NAMING COMPOUNDS WITH MULTIVALENT
IONS


When writing names with a multivalent ion, you
must indicate which version of the element you
are using. (The first listed is always more
common)
Example:
Titanium and oxygen
 Ti+3 and O-2
 Ti2O3
 Titanium (III) oxide

(elements)
(ions)
(chemical formula)
(name)
JUST BE CAREFUL WHEN…


Your elements have even numbers of atoms and
they have been simplified.
Example:


TiO2 = Titanium (IV) oxide
Remember…
Titanium (IV) oxide
 Ti+4 and O-2
 Ti2O4  simplified to  TiO2

PRACTICE TIME!
Chemical Formula
1.
2.
ANSWERS
Chemical Name
NaCl
Sodium chloride
BeO
Beryllium oxide
K2S
Potassium sulfide
LiF
Lithium fluoride
CaBr2
Calcium bromide
AgI
Silver iodide
PbCl2
Lead (II) chloride
MgO
Magnesium oxide
BaI2
Barium iodide
LiBr
Lithium bromide
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
ANSWERS
MgCl2
Magnesium chloride
CuO
Copper (II) oxide
K2S
Potassium sulfide
VBr5
Vanadium (V) bromide
CsI
Cesium iodide
MnS2
Manganese (IV) sulfide
MnS
Manganese (II) sulfide
AuI3
Gold (III) iodide
Pt3P2
Platinum (II) phosphide
Tl2O3
Thallium (III) oxide
13.
14.
15.
16.
17.
18.
19.
20.
MOLECULAR COMPOUNDS
DEFINITIONS

Molecule


The smallest independent unit of a pure substance and is
generally a cluster of atoms joined together.
Diatomic molecules
Molecules made up of two atoms of the same element.
 These atoms can never be alone, if they aren’t bonded with
another element, they bond with another identical atom.
 7+1 Rule: In the shape of a 7 + Hydrogen on the periodic
table



Nitrogen, Oxygen, Flourine
Chlorine
Bromine
Iodine
They create N2, O2, F2, Cl2, Br2, I2, H2
PROPERTIES OF MOLECULAR COMPOUNDS





Composed of two or more non-metals
They can be solids, liquids or gases
They tend to be insulators, or poor conductors
The forces between the molecules are weak bonds
They share electrons
HOW MOLECULAR COMPOUNDS ARE
FORMED

Molecular compounds share electrons instead of
transferring them.
Oxygen has 6 valence electrons
 Hydrogen has 1 valence electron.


If Oxygen shares electrons with two atoms of
hydrogen, oxygen can have 8 electrons and each
hydrogen can have 2 electrons – full shells for both

Example: Water
MOLECULAR COMPOUND EXAMPLES
Diatomic molecule
Diatomic molecule
NAMING MOLECULAR FORMULAS
Write the name of the first element.
2.
Change the name of the second element to end with the suffix
“ide”
3.
When there is more than one atom in the formula, add a prefix to
indicate the number of atoms. Some are listed below.
 Exception: When the first element has only one atom, the prefix
mono is not used.
1.
WRITING FORMULAS FOR MOLECULAR
COMPOUNDS
Unless you’re given the name, writing formulas
for molecular compounds are tricky because they
don’t deal with charges.
 Why don’t they deal with charges?



Because there are no ions (nothing has given or taken
electrons).
We won’t deal with writing formulas without the
names. Just make sure you can convert the name
to the chemical formula and back again.
DRAWING MOLECULAR COMPOUNDS

Glucose
Cocaine

Ethanol
Caffeine
Propane
Acetaminophen
HOWEVER…


All you’ll have to draw is something like this
NH3
H
H2
H–H
BrO2
N
H
Br
H
O
O
PRACTICE TIME!!!
ORGANIZING BONDING
Monovalent
Ionic
Multivalent
Ionic
Polytomic
Ionic
Molecular
Dealing with
Electrons
Give/take
Give/take
Give/take
Share
Chemical
Formulas
Cross charges
into subscripts
Cross charges
into subscripts
Cross charges
into subscripts –
put brackets
around polytomic
ion
Write the
subscript that
corresponds to
the prefix.
Naming
Metal +
nonmetal with –
ide ending
Metal + Roman
numeral
indicating charge
+ nonmetal with
–ide ending
Metal +
polytomic ion
name (no name
change)
Turn the
subscript
number into a
prefix name.
Example
NaCl
Sodium chloride
AuI3
Gold (III) iodide
Au2(CO3)3
Gold (III)
carbonate
F2O
Difluorine
monoxide