OB: molecular compounds,
naming and formulas, and
determining how for form
molecular compounds using
selected oxidation states.
Periodic tables mandatory now,
smile, this is easier than the rest
of the compounds we’ve looked at
Ionic compounds form when positive cations combine in proper ratio
with negative anions, attracting each other because of opposite charge.
The compounds must have a cation combining with anions
(+ except for that weird ammonium) all cations are metals.
With molecular compounds, the easy way to spot
them is that there are NO METALS.
Molecular compounds form when 2 or more nonmetals
bond together,in proper ratios.
There are NO ions, no ionic bonds either.
They combine by sharing electrons which we’ll learn about later on in
the year. They have their own naming system, which is easy if you
can count to ten in Latin.
If you can’t, I will teach you in a few slides.
CO2
NH3
CO
CH4
HCl
H2O
There are NO METALS ever
in molecular compounds.
C8H18
When two or more non metals bond
together they form a molecule.
A molecule is the smallest part of a
molecular compound. The bonds that
hold these atoms together is called a
covalent bond.
When 2 or more ions bond, they make
ionic bonds, and they form into
FORMULA UNITS. NaCl does not come in
molecules, since it does not exist as a
single particle. It’s in crystals, or
dissolved in water.
NAMING RULES FOR MOLECULAR COMPOUNDS
If you can remember what CO, CO2, and H2O are,
the naming rules are easy
carbon monoxide, carbon dioxide +
dihydrogen monoxide
First name rule:
a single atom? Say just the atom name
a multiple atom? Say a prefix first
Second name rule: always use a prefix
1 MONO
6 HEXA
2 DI
7 HEPTA
3 TRI
8 OCTO
4 TETRA
9 NON
5 PENTA
10 DECA
Using the 2 rules, and the Latin Prefixes, let’s name these 10 example molecules.
You will have to name any molecular compound with up to 10 atoms of any kind.
HF
CS2
SO3
CCl4
PF5
SF6
Cl2O8
I4O9
N2F10
Hopefully you got these all correct…
HF
Hydrogen monofluoride
CS2
Carbon disulfide
SO3
Sulfur trioxide
CCl4
Carbon tetrachloride
PF5
Phosphorous pentafluoride
SF6
Sulfur hexafluoride
Cl2O8
Dichlorine octoxide
I4O9
Tetraiodine nonoxide
N2F10
Dinitrogen decafluoride
First name rule for
single atom is say
that atom name.
Multiple atoms in
first name gets a
prefix.
Second name rule
says always use a
prefix.
We will practice names to formulas first…
Write the formulas for each named molecule:
Phosphorous tribromide ____________
Diphosphorous trioxide ____________
Oxygen difluoride _____________
Dihydrogen monoxide ______________
Nitrogen monoxide ______________
We will practice names to formulas first…
Write the formulas for each named molecule:
Phosphorous tribromide
PBr3
Diphosphorous trioxide P2O3
Oxygen difluoride
OF2
Dihydrogen monoxide H2O
Nitrogen monoxide
NO
Now in reverse, name these formulas with prefixes…
NO2 _________________________
CI4
_________________________
N20 _________________________
SO3 _________________________
N2O5 _________________________
HCl
_________________________
Now in reverse, name these formulas with prefixes…
NO2 nitrogen dioxide
CI4
carbon tetraiodide
N20 dinitrogen monoxide
SO3 sulfur trioxide
N2O5 dinitrogen pentoxide
HCl
hydrogen monochloride
Look right now at tables K and L
These are the acids and bases. We will spend about two weeks on what acid and
base chemistry is all about, but today we will look at their names, see that their
names and formulas are on your reference tables, say the names together, and
that’s that.
Also, there are 7 elements that exist NOT as atoms in their natural state. Rather
they exist as pairs of atoms, diatomic elements.
Mr. Smith taught this to me in the 8th grade at Junior High School 202 in Ozone Park
in Queens. I am happy to share his wisdom now.
To remember these seven diatomic elements, we will call them the
HONClBrIF twins
H2 O2 N2 Cl2 Br2 I2 F2
How do we decide what ratios of nonmetal
atoms fit together to make compounds?
Why is water H2O and NO OTHER
hydrogen-oxygen compounds exist in any
other ratio?
Thinking hats on now.
Periodic Tables, Selected Oxidation States
These numbers tell us (with some thinking) what ratios are possible, and what
ratios cannot create molecules.
Make this chart in your notes:
H
O
Write in all of the possible oxidation states from the Periodic Table of the Elements
H
+1
-1
O
-2
2:1 ratio possible
X: two negatives ≠ 0
The only possible combo for H and O to
bond is 2:1, which spells in chemistry:
H2O
Let’s determine all of the possible carbon +
oxygen compounds that could form with the
selected oxidation states. Remember: they
must sum to zero, but the ARE NOT IONS.
These atoms share electrons only.
C
O
Let’s determine all of the possible carbon +
oxygen compounds that could form with the
selected oxidation states. Remember: they
must sum to zero, but the ARE NOT IONS.
These atoms share electrons only.
C
-4
+2
+4
O
-2
Let’s determine all of the possible carbon + oxygen compounds that could
form with the selected oxidation states. Remember: they must sum to
zero, but the ARE NOT IONS. These atoms share electrons only.
There is NO WAY -4 plus -2 can ever sum to zero, this selected oxidation
state for carbon is not used in any carbon – oxygen compounds.
C
-4
+2
+4
O
-2
1:1 is possible
1:2 is also
CO + CO2 are possible, nothing else is
according to our periodic table.
Let’s do the big one: All Nitrogen + Oxygen Compounds (there are 5)
N
O
Let’s do the big one: Nitrogen and Oxygen
N
-3
-2
-1
+1
+2
+3
+4
+5
O
-2
Let’s do the big one: Nitrogen and Oxygen
N
-3
-2
-1
+1
+2
+3
+4
+5
O
5 Possible Compounds
2:1 or N2O
-2
1:1 or NO
2:3 or N2O3
1:2 or NO3
2:5 or N2O5
This week…
THURSDAY we will have a major review, then a celebration
on naming compounds and formulas on FRIDAY
Friday we start moles, bring a calculator, you’ll need it.
This man is on
Double Secret Probation.
do you know who this is?