Transcript Formula - SandersScienceStuff

A. Definition
• Remember, a compound
consists of 2 or more elements
chemically bonded together. It
is always neutral.
EX: H20, NaCl, Sb3(PO4)5
• There are two main ways to name
chemical compounds. However,
before you can even think about
naming the compound you must
decide what kind of compound
you have. Do you have a
covalent or ionic compound? We
already learned this using the
terms molecule and formula unit.
• Most formulas are written with
the elements listed from left to
right on the periodic table
What do you remember about
the difference between a
molecule and a formula unit?
B. Types of Compounds
2 types of chemical
compounds
Samples
Ionic Compounds Molecular Compounds
• Rock salt (NaCl)
• Calcium Carbonate
(CaCO3)
• Potassium Nitrate
(KNO3 )
• Sugar (C12H22O11)
• Methane gas (CH4)
1. Ionic Compound:
Ionic Compound: a compound that is
formed by ions of opposite charges. It
is held together by an ionic (transfer
electrons) bond and usually contains a
metal and nonmetal.
EX: NaCl, Sb3(PO4)5
smallest unit is called a
formula unit
2. Molecular or Covalent
Compound:
•
Molecular or Covalent compound:
consists of only nonmetal atoms and
is held together by covalent (share
electrons) bonds
EX: H20, C8H18
smallest unit is called a
molecule
How can I tell!?
• Look for a metal.
• If there’s a metal, it’s an ionic
compound
Practice
1. Determine whether the following
are ionic or molecular covalent
compounds
a. N2O5 molecular
b. PbNO
PbNO55 ionic
c. KF
ionic
e. PCl3
molecular
d. AgCl
ionic
Acids: have a formula that starts
with hydrogen
You need to know the names and formulas for the
following acids:
Acid Name
Formula
hydrochloric acid
HCl
nitric acid
HNO3
sulfuric acid
H2SO4
phosphoric acid
H3PO4
Note: all acids start with “H” in their chemical
formulas and include the word “acid” in their
names.
II. Molecular
Compounds
(aka Covalent Compounds
aka Molecules)
Molecular Compounds = share electrons
HO
H
H2O
A. Binary Molecular Compounds
• Molecular compounds DO NOT
contain a metal atom
• Molecular compound contain
covalent bonds
• We use prefixes to name
molecular, ONLY MOLECULAR,
compounds
How do I distinguish between the
bikes?
unicycle
bicycle
tricycle
We use prefixes to help distinguish
molecular compounds.
Prefix
Number of Atoms
mono
1
di
2
tri
3
tetra
4
penta
5
hexa
6
hepta
7
octa
8
nona
deca
9
10
Why have prefixes?
Nitrogen bonds to Oxygen in more
than one way
Ex: N2O, NO2, N2O2, N2O5
Examples:
Formula: CO
Name: carbon monoxide
Formula: N2O
Name: dinitrogen monoxide
a. Naming binary molecular
compounds:
FIRST ELEMENT IN THE FORMULA
–
–
keeps its full elemental name
Add prefixes to signify the number of that
specific kind of atom ONLY if there is more
than one of the atoms. DON’T USE MONO
ON THE FIRST SYMBOL
SECOND ELEMENT IN THE FORMULA
–
–
The second element name ALWAYS gets a
prefix
Keep the first syllable of the
elemental name and change the
suffix to “ide”.
Practice:
Formula: CO2
name: Carbon dioxide
Formula: BF3
name: Boron trifluoride
Formula: Cl2O
name: Dichlorine monoxide
Formula: P2S5
name: Diphosphorus pentasulfide
B. Converting a name to a formula:
• This exercise is very simple if
you have memorized the
element symbols and the
prefixes. Just go backwards
from what we just did.
Examples:
Formula: CCl4
Name: carbon tetrachloride.
Formula: H2F
Name: dihydrogen monofluoride
Practice:
Formula: H2O
name: Dihydrogen monoxide
Formula: NO5
name: Nitrogen pentoxide
Formula: CF4
name: CarbonTetrafluoride
Formula: SiO2
name: Silicon Dioxide
1+
2+
3+
3-
2-
1-
III. Naming ions
1. Monatomic Cations
(+
ions)
+
One
atom
• Monatomic cations are named by
writing the element’s name and then
“ion” after it.
• EX:
Ca2+
Calcium
ion
Na+
Sodium
ion
a. Monatomic Cations
(Transition + PASS + Z.A.C Elements )
• Most transition metals and
“P.A.S.S” elements need
Roman Numerals
• Zinc (Zn), Silver (Ag), and
Cadmium (Cd) are transition
metals that DO NOT need
Roman Numerals
More than just “Iron ion”
EX: Fe2+
Iron (II) ion
Fe3+
Iron (III) ion
Transition Metals need R.N.
1. Name these ions
4+
a. Pb
Lead (IV) ion
b. Pb2+
Lead (II) ion
+
c. Cu
Copper (I) ion
d. Cu2+
Copper (II) ion
Examples
1. Name these ions
2+
a. Ca
Calcium ion
b. Na+
Sodium ion
4+
c. Fe
Iron (IV) ion
d. Zn2+
Zinc ion
b. Monoatomic Anions (- ions)
oMonatomic anions are
named by changing the
suffix to “ide” then adding
“ion” after it.
Cation or Anion?
• Carbon can act as a cation (carbon ion)
or as an anion (carbide ion). It just
depends if it is in the beginning or the end
of the compound’s formula
• Hydrogen can also act as a cation
(hydrogen) or as an anion (hydride). It
just depends if it is in the beginning or the
end of the compound’s formula. Don’t
forget it is a non-metal.
Complete the chart below
Element
Symbol
Oxidation
number
Anion name
Chlorine
Cl-
-1
Chloride ion
Bromine
Br-
-1
Bromide ion
Oxygen
O2-
-2
Oxide ion
Sulfur
S2-
-2
Sulfide ion
Phosphorus
P3-
-3
Nitrogen
N3-
-3
Phosphide ion
Nitride ion
Summary
• List the elements that need
Roman Numerals
Transition metals, PASS elements
(Pb, As, Sn, Sb)
• List the transition metals that
don’t need Roman Numerals
Zn, Ag, Cd (Z.A.C elements)
Anions: Change Suffix to -ide
always
1+
2+
3+
3-
2-
1-
Zn2+ Ag+ Cd2+
Always need roman numerals
Tips
TM (Except ZAC) and PASS need Roman Numerals
All metals are +; all non-metals are Anions end in -ide
c. Polyatomic Cations
• A polyatomic ion is a group of
covalently bonded atoms that
have an overall charge
• Example
NH4+ = ammonium.
d. Polyatomic Anions
•
This means the anion is a
COVALENTLY BONDED GROUP
of atoms that have a – charge.
They are EASY to deal with in
naming and formula writing if
you think of them as ONE UNIT
that can not be altered in any
way.
Example:
• Use the back of your periodic
table to help you identify
polyatomic anions
Flip over your PT and let’s practice
1. Name these ions
2carbonate
a. CO3
hydroxide
b. OHnitrate
c. NO3d. SO42sulfate
phosphate
e. PO43-
IV. Binary Ionic Compounds
a. Naming Binary Ionic Compounds
• Ionic Compounds are made of a
cation and anion pair. You already
know how to name the ions. Just put
the names together and leave off the
word ion. Don’t forget Roman
Numerals!
Ionic Compounds = transfer of electrons
+
Na
Cl
NaCl
Is formed
-
a. Naming Binary Ionic Compounds
Formula
Ions
Ion names
Compound name
AlN
Al3+
N3-
Aluminum ion
Nitride ion
Aluminum nitride
Na20
Na+
O2-
Sodium ion
Oxide ion
Sodium oxide
FeO
Fe2+
O2-
Iron (II) ion
Oxide ion
Iron (II) oxide
Fe2O3
Fe3+
O2-
Iron (III) ion
Oxide ion
Iron (III) oxide
Ex. Name FeS
NOT Iron Sulfide
Iron (II) sulfide
Remember to add a Roman Numeral
for the cations that need one
One trick to determine the Roman
Numeral:
1. Add up your total negative charges
2. Divide the above number by the total
number of metal ions
3. Change to a Roman
Numeral
1. Add up your total negative charges
2. Divide the above number by the total
number of metal ions
3. Change to a Roman
Numeral
Ex. Name FeS
Total neg. charges: 22/1 (Fe) = 2
Iron (II) Sulfide
Ex. Name Fe2O3
Total neg. charges: 66/2 (Fe) = 3
Iron (III) Oxide
Practice
1. Name the following compounds
a. ZnS
Zinc sulfide
b. K3N
Potassium nitride
c. BaO
Barium oxide
d. CaBr2
Calcium bromide
e. SnF2
Tin (II) fluoride
Practice
1. Name the following compounds
f. CaO
Calcium oxide
g. AlF3
Aluminum fluoride
h. CuI2
Copper (II) iodide
i. Cu2Se
Copper (I) Selenide
j. Hg2O
Mercury (I) Oxide
b. Writing Formulas for Binary Ionic
Compounds
• Remember, a compound must
be electrically neutral.
Therefore, the total positive
charge of the cation must
equal the total negative charge
of the anion.
EX: calcium chloride
Ca2+ ClTo make a neutral compound
Ca2+ ClCl+2
-2
CaCl2
To write a formula for a binary ionic compound
1.Write the ions that are named in the compound showing
oxidation numbers.
2. Determine how many of each ion you need to make a
neutral compound.
3. To write the formula, list the metal symbol first and then
the anion symbol, adding subscripts to indicate how many of
each ion there is in the formula
4. Make sure the formula has the lowest whole number ratio.
Note: you never write a 1 subscript; it is understood.
EX: write the formula for
aluminum fluoride
Al+3
+3
FFF-3
Formula: AlF3
NOTE: You never include
oxidation numbers in the
chemical formula of a
compound.
Practice – only do a-c
1. Write chemical formulas for
the following:
a. strontium phosphide Sr3P2
b. potassium sulfide K2S
c. iron (II) chloride FeCl2
The Criss-Cross Method
• One easy way to figure out the
formula of an ionic compound is
to swap the oxidation number of
each ion and use them as
subscripts. (without the charge)
• the formula must be in the
lowest whole number ratio
Just Watch!!
sodium sulfide
Na
1+
1’s are understood
S
2-
Criss Cross Method
Na2S
Ex: Write the formula for
iron (III) bromide
Fe
3+
Br
-
Criss Cross Method
FeBr3
Note: if both ox #’s are equal, you
don’t need to use the crisscross
method, just show 1 ion of each.
Ex: Write the formula for
magnesium sulfide
Mg
2+
S
2-
Magnesium Sulfide
MgS
Note: show the formula with the lowest
whole number ratio.
EX: write the formula for lead
(IV) sulfide
Pb
4+
S
2-
Criss Cross Method
Pb2S4
PbS2
Finish the Practice Box
1. Write chemical formulas for
the following:
d. antimony (V) nitride Sb3N5
e. iron (III) chloride FeCl3
f. Calcium bromide CaBr2
Naming
• Same way as
you already
learned
Formulas
• Use subscripts to
show how many
of each ion you
needed to make a
neutral compound
V. Ionic Compounds Containing
Polyatomic Ions
a. Writing Formulas for Polyatomic
Compounds
• Write formulas for polyatomic ions in
the same way. Just remember the
polyatomic ion acts as a whole unit
and you need to use parentheses
if you need more than 1 of them.
• Note: You never change the
• formula of a polyatomic ion!
EX: calcium nitrate
To make a neutral compound
Ca2+ (NO3)(NO3)+2
-2
Ca(NO3)2
EX: Calcium Nitrate
(using the criss cross method)
2+
Ca (NO3)
-
Practice
Practice
1. Write formulas for the following
compounds
a. strontium sulfate
SrSO4
b. lithium carbonate
Li2CO3
c. potassium sulfate
K2SO4
d. magnesium hydroxide Mg(OH)2
Practice
Practice
1. Write formulas for the following compounds
e. ammonium dichromate (NH4)2Cr2O7
f. potassium permanganate KMnO4
g. sodium hypochlorite NaClO
h. barium sulfite BaSO3
b. Naming Polyatomic Compounds
• It is important that you recognize
the polyatomic
• If there are more than 2
elements in the formula, then you
know it contains a polyatomic.
• Only one polyatomic is a cation,
ammonium (NH4+) All the rest will
come after the metal ion.
• You name polyatomic
compounds just like you would
other ionic compounds -- you
write the name of each ion.
Note: most (not all) polyatomic
compounds will end in -ate or
-ite.
Ex. Name ZnSO4
Zinc Sulfate
Ex. Name NaOH
Sodium hydroxide
Practice
1. Name these compounds
a. CaCO3
calcium carbonate
b. KClO
potassium hypochlorite
c. KMnO4
potassium permanganate
Practice
1. Name these compounds
d. Al(OH)3
aluminum hydroxide
e. Sn3(PO4)2
tin (II) phosphate
f. Na2CrO4
sodium chromate