Unit 5 Powerpoint

download report

Transcript Unit 5 Powerpoint

Naming and Formula Writing
What’s in a name?
Quick Review
What do metals want to do?
– So what do they become?
What do nonmetals want to do?
– So what do they become?
What do opposites do?
Naming Ions
Ionic Compounds
– Consist of a (+) metal ion and a (-)
nonmetal ion combined in a proportion
such that their charges add up to 0.
Monatomic Ions
Consist of a single ion with a positive
or negative charge resulting from the
loss or gain of one or more valence
electrons
Cations
When the metals in groups 1A, 2A, 3A
lose electrons, they form cations with
positive charges that equal their group
number.
Their names are the same as the
metal followed by “ion” or “cation”
Anions
Nonmetals tend to gain electrons to
form anions, so the charge of a
nonmetallic ion is negative.
Anions- Naming
Anion names start with the stem of the
element name and end in –ide
F- =
– Fluoride
N3- =
– Nitride
The majority of elements in groups
4A and 8A usually do not form ions.
– Why?
Oxidation Numbers
Found in the upper right-hand corner of
the element’s box in the Periodic Table
These numbers indicate what the
element tends to do with electrons when
bonding
Oxidation Number Rules
1. For an atom alone or bonded to itself
(diatomics), the oxidation number for
each of those atoms is 0.
Oxidation Number Rules
2. For a simple ion, the oxidation number
is its charge (given in the Periodic
Table)
chloride=
aluminum ion=
oxide=
barium ion=
fluoride=
potassium ion=
sulfide=
iron (II)=
carbide=
manganese (IV)=
Oxidation Number Rules
3. Oxygen usually has an oxidation number of
-2.
CaO=
Exceptions:
When bonding with fluoride (which is more
EN), oxygen is forced to donate electrons,
becoming +2  OF2
In peroxides, like hydrogen peroxide, each
oxygen has a -1 oxidation number:
H2+1O2-1 (peroxide is a polyatomic ion)
Oxidation Number Rules
4. Hydrogen usually has an oxidation
number of +1.
H2O=
Exception: Metal hydrides.
When hydrogen bonds with a group 1 or
group 2 metal its oxidation is -1
NaH=
• Why?
Oxidation Number Rules
5. The sum of all the oxidation numbers in
a neutral compound must add up to
zero.
NaCl=
6. The sum of all the oxidation numbers in
a polyatomic ion must add up to equal
the charge of the ion.
CO3-2=
Ions of Transition Metals
Many form more than one cation with
different ionic charges.
The charges of the cations of many
transition metal ions must be
determined by the number of
electrons lost.
Ex. Fe2+ and Fe3+
Two methods of naming:
1. STOCK SYSTEM (preferred)
•
A Roman numeral in parentheses is
placed after the name of the element to
indicate the numerical value of the
charge.
•
•
Fe (II)- “iron two ion”
Fe (III)- “iron three ion”
2. Use a ROOT WORD with different
suffixes
•
ferr•
•
-ous (II)
-ic (III)
Some Transition Metals….
Have only 1 ionic charge:
– Ag+
– Cd2+
– Zn2+
we like these
because they’re easy!
Polyatomic Ions
Composed of more than one atom
Tightly bound group of atoms that
behaves as a unit and carries a charge
Names of most p.i. end in –ite or –ate
Atoms in polyatomics are sharing
electrons
Three important ions have
different endings:
NH4+ = ammonium
CN- = cyanide
OH- = hydroxide
-ites and -ates
Sulfite: SO32Nitrite: NO2Chlorite: ClO2-
Sulfate: SO42Nitrate: NO3Chlorate: ClO3-
ONE LESS
OXYGEN ATOM
ONE MORE
OXYGEN ATOM
Polyatomics with hydrogen
Think of H representing a hydrogen ion (H+)
combined with another polyatomic ion
H+ + CO32-  HCO3- (hydrogen carbonate)
H+ + PO43-  HPO42- (hydrogen phosphate)
H+ + HPO42-  H2PO4- (dihydrogen phosphate)
COMPOUNDS
Early things named by people who
discovered them- usually based on
properties:
– Ex. NaHCO3 = baking soda
Binary Compound
Is composed of two elements and can
either be either ionic or molecular
(covalent)
Antoine-Laurent Lavoisier
Determined the composition of many
substances.
Worked with other chemists to develop
a systematic method for naming
chemical compounds.
Compound: M+ and NMYou must make sure that the
compound is composed of a
monatomic metallic cation and
monatomic nonmetallic anion.
Name the cation first, followed by the
anion.
Cs2O
cesium oxide
NaBr
sodium bromide
SrF2
strontium fluoride
What about compounds with
elements that form multiple ions?
CuO
Cu+
Cu2+
O2-
copper (II) oxide
Examples
FeO
Fe2O3
Mn2O7
Compounds- FORMULAS
Write the symbol of the cation and then
the anion.
Add whatever subscripts are needed
to balance the charges (compounds
must be neutral)
K+ + Cl-  KCl
Criss-Cross Method
Fe3+
O2Fe2O3
Charge on one element becomes
subscript on other, and vice versa
2(3+) + 3(2-) = 0
iron (II) oxide
Ca2+
CaS
Charges balance
1:1 ratio
Calcium sulfide
S2-
Compounds with Polyatomic Ions
Write the symbol for the cation followed
by the formula for the polyatomic ion
and balance the charges.
Ca2+
(NO3)1Ca(NO3)2
calcium nitrate
Naming Compounds with
Polyatomic Ions
You must first recognize that the
compound contains a polyatomic
ion.
State the cation first and then the anion
just as you did in naming other
compounds.
– LiCN= lithium cyanide
– NaClO= sodium hypochlorite
A little different…
Some compounds containing
polyatomic ions do not include a metal.
They have the ammonium cation
instead.
– NH4+
EXAMPLE: NH4CH3COO
– Ammonium acetate
Compounds: NM + NM
2 nonmetals
Naming NM + NM
Compounds
The prefix tells how many atoms of
each element are present in a molecule
of a compound
Prefixes you must know
Mono- 1
Di- 2
Tri- 3
Tetra- 4
Penta- 5
Hexa- 6
Hepta- 7
Octa- 8
Nona- 9
Deca- 10
Still on nonmetal compounds
Names all end in -ide
N2O- dinitrogen monoxide (laughing
gas)
Rules
1. Confirm that the compound contains 2
nonmetals
2. Name the elements in the order listed in the
formula
3. Use the prefixes to indicate the number of
each kind of atom
4. Omit the prefix mono- when the formula
contains only one kind of the first
element in the name
•
Carbon monoxide (CO)
Example
Cl2O8
dichlorine octoxide
Formulas
Use the prefixes in the name to tell you the
subscripts of each element in the formula.
Then write the correct symbols for the two
elements with the appropriate subscripts.
Phosphorus pentafluoride
– PF5
Dinitrogen tetroxide
– N2O4
ACIDS
Acid- a compound that contains one or more
hydrogen atoms and produces hydrogen
ions when dissolved in water.
Consider the acid to consist of an anion
combined with as many hydrogen atoms are
needed to make the molecule electrically
neutral.
HnX (where X is a mono or polyatomic anion)
Acids- Three Rules
1. When the name of the anion ends in
-ide:
 the acid name begins with the prefix
hydro-.
 The stem of the anion has the suffix -ic
and is followed by the word ACID.
EXAMPLE- HCl= hydrochloric acid
Acids- Three Rules
2. When the anion name ends in –ite:
 the acid name is the stem of the anion
with the suffix -ous
 followed by the word ACID.
EXAMPLE- H2SO3- sulfurous acid
Acids- Three Rules
3. When the anion name ends in –ate:

the acid name is the stem of the anion
with the suffix -ic
 followed by the word ACID
EXAMPLE- HNO3- nitric acid
Acids- Formulas
Use the rules for writing the names of
acids in reverse to write the formulas for
acids
Hydrobromic acid =
– HBr
Phosphorous acid =
– H3PO3
BASES
Base- an ionic compound that produces
hydroxide ion when dissolved in water.
Bases are named the same way as other
compounds that contain a M+ and NM- (or
polyatomic)– The name of the cation is followed by the name of
the anion.
Aluminum hydroxide
– Al(OH)3
The Law of Definite
Proportions
In samples of any chemical compound,
the masses of the elements are
always in the same proportions.
The Law of Multiple
Proportions
Whenever the same two elements form
more than one compound, the different
masses of one element that combine
with the same mass of the other
element are in the ratio of small
whole numbers.
Some reminders
1. An -ide ending generally indicates a binary
compound (TWO ELEMENTS)
2. An -ite or -ate ending means a polyatomic
ion that includes oxygen in the formula
3. Prefixes in a name generally indicate that
the compound is made of two or more
nonmetals
4. A roman numeral after the name of a cation
shows the ionic charge of the cation