I. REVIEWING IONS
1. Ion = atom or a group of bonded atoms
with a positive or negative charge.
I. REVIEWING IONS
2. Cation = ion with a POSITIVE (+) charge.
a) Forms when an atom LOSES one or more
valence electrons
b) Ex: Be+2 forms b/c beryllium
___________valence
electrons
loses 2
I. REVIEWING IONS
Be has the following electron configuration:
1s22s2
o How many VALENCE electrons does Be
have?
2 valence electrons
_____
I. REVIEWING IONS
How many protons and electrons does a Be
atom have?
4 protons and ____
4 electrons
o ____
How many protons and electrons does Be+2
have?
2
4
o ____protons and ____electrons.
o Creating a +2 ion
I. REVIEWING IONS
3. Anion = ion with a NEGATIVE (-) charge.
a) Forms when an atom GAINS one or more
valence electrons
b) Ex:
F-1
gains
1
forms b/c fluorine _______
valence electron
I. REVIEWING IONS
F has the following electron configuration:
1s22s22p5
o How many VALENCE electrons does F
have?
7 valence electrons
____
I. REVIEWING IONS
How many protons and electrons does the F
atom have?
9 protons and _____
9 electrons
o ____
How many protons and electrons does F-1
have?
9
10
o _____ protons and _____electrons.
o Creating a -1 ion
I. REVIEWING IONS
4. Monatomic Ion = ion formed from only ONE
atom
a) Ex: Na+1, Ca+2, N-3, F-1
b) Note: All monatomic anions end in
Ex: atom = oxygen; ion = oxide
Ex: atom = chlorine; ion = chloride
Ex: atom = sulfur; ion = sulfide
–ide
I. REVIEWING IONS
5. Polyatomic Ion = ion formed from two or
more atoms bonded together with a charge.
a) Ex: SO4-2, Hg2+2, OH-1, CN-1
I. REVIEWING IONS
6. Classify the following as monatomic anion,
monatomic cation, polyatomic anion, or
polyatomic cation.
a) Li
+1
Monatomic cation
= __________________
b) O2-2 = __________________
Polyatomic anion
Polyatomic cation
c) NH4+1 = __________________
Monatomic anion
d) S-2 = __________________
I. REVIEWING IONS
7. REMEMBER- Rules For Assigning Ion
Charges:
I. REVIEWING IONS
8. Roman Numerals
Sometimes an atom is able to give away a
various number of electrons and be stable
The Roman numerals tell how many electrons
have been given away and that will be the
POSITIVE charge
Ex: iron (II) and iron (III)
Fe
+2
and Fe
+3
II. WRITING IONIC FORMULAS
1. Ionic compounds
are formed by two
ions of opposite
charge (cations are
+ and anions are -)
and that they are
held together by a
relatively weak
attraction between
the ions.
II. WRITING IONIC FORMULAS
2. KEY IDEA-Ionic Compounds:
Usually metal and nonmetal elements
combine
Are NEUTRAL compounds
II. WRITING IONIC FORMULAS
The simplest whole number ratio between the
cation & anion creates the ionic formula
The net charge is zero, forming a neutral ionic
compound.
Ex: MgCl2
1 magnesium ion : 2 chloride ions
Ex: KBr
1
1
____potassium
ion : ____bromide
ion
Ex: Ca3(PO4)2
2
3
_____calcium
ions : ____ phosphate ions
II. WRITING IONIC FORMULAS
3. Care must be taken that subscripts are
correct
Ex: NaCl vs. CaCl2
II. WRITING IONIC FORMULAS
4.Why does the chlorine have a subscript
of “2” in one chemical formula but not in
the other?
Look at the ion charges!
Look at the ION charges!
+1
-1
Na
Cl
Sodium is _____ and chloride is _____
A +1 and a -1 charge form an ionic
compound with a zero charge!
-1
Cl
Calcium is _____ and chloride is _____
Ca+2
NOW 2 chloride ions are needed in
order to form a neutral compound
II. WRITING IONIC FORMULAS
5. All IONIC compounds are neutral. So
the algebraic sum of the charges has to
equal zero!
II. WRITING IONIC FORMULAS
Ex: Aluminum sulfate has the following
chemical formula: Al2(SO4)3
A chemical formula for this ionic
compound shows that 2 Al+3 ions and 3
SO4-2 ions are needed in order to form
a neutral compound.
6. Examples of Forming Ionic Compounds
Example #1: Write a formula for aluminum
chloride.
What are the charges of the ions?
+3
-1
Al
Cl
_____ and ____
What do the charges mean?
loses 3
Aluminum _________
electrons
gains 1
Chlorine _________electron
How is aluminum chloride formed?
Use electron-dot formulas to illustrate the
formation of ionic bonds involving Al and Cl.
How is aluminum chloride formed?
It takes 3 chlorine atoms to gain the 3
electrons that one aluminum atom can donate.
When this transfer occurs, 1 aluminum ion will
be formed and three chloride ions will be
formed.
These particles will all be held together by the
opposite electrostatic charges.
The formula is AlCl3.
Think of writing an
ionic formula as looking
for a lowest possible
ratio of positive and
negative ions that need
to combine in order to
form a neutral compound!
Example #2: Write a formula for
sodium sulfide.
What are the charges of the ions?
Na+1 and _____
S-2
______
What is the ratio or combination that these
ions must form in order to form a NEUTRAL
compound?
1
2
____sodium
ions and ___sulfide
ion
Write the formula for sodium sulfide: Na
____
2S
7. Rules for writing ionic formulas:
1. The subscript 1 is understood when NO
subscript is present and is not written
2. Use parentheses around polyatomic
ions when adding additional subscripts
PROTECT POLYATOMICS WITH
PARENTHESES!!
( parentheses )
7. Rules for writing ionic formulas:
3. Write the symbol for the positive ion
(cation) first, following by the negative ion
(anion)
4. Determine the simplest whole number
ratio between the cation & anion
7. Rules For Writing Ionic Formulas:
Use the “criss-cross” method- the NUMBERS
of the positive and negative charges can be
“crossed” over to give the correct subscripts
to the opposite ion.
II. WRITING IONIC FORMULAS
• Ex #1: What is the formula of the
compound formed by the ions of
magnesium and bromine
bromine?
Ions =
+2
Mg
and
-1
Br
Formula = Mg Br2
II. WRITING IONIC FORMULAS
Ex #2: Aluminum Sulfide (use the
“criss-cross” method)
+3
-2
Al
S
Ions = ________
Al2 S 3
Formula = _______
II. WRITING IONIC FORMULAS
Ex #3: Magnesium oxide
+2 O-2
Mg
Ions = ________
O
Formula = Mg
_____
2
2
We must reduce this to the lowest
terms!
MgO
The final answer is ______
II. WRITING IONIC FORMULAS
Ex #4: Sodium peroxide
Polyatomic – NO parentheses and NO
reduction
+1
-2
Na
O
2
Ions = ___________
Na 2 O2
Formula = _______
NO REDUCTION -This is the correct
formula for this compound since we cannot
reduce a subscript which is already set as a
part of the original ion!
II. WRITING IONIC FORMULAS
Ex #5: Copper II sulfate
Polyatomic – NO parentheses and
reduction
Cu+2
SO4-2
Ions = _______________
CuSO4
Formula = ___________
II. WRITING IONIC FORMULAS
Ex #6: Calcium nitrate
polyatomic- PROTECT with
PARENTHESES
You cannot alter the subscripts that come
with polyatomic ions, we use parentheses!
+2
-1
Ca
NO
Ions = ___________
3
Ca (NO3) 2
Formula = _________
II. WRITING IONIC FORMULAS
Note: NEVER use parentheses around
monatomic ions (Na, Li, Fe, Cu, etc).
Only polyatomic ions (SO4, MnO4,
NH4, PO3, etc.) will ever require the
use of parentheses.
II. NAMING IONIC COMPOUNDS:
1. Rules:
a) Determine the name of the cation & anion
that is present
Positively charged ion name comes 1st
Negatively charged ion name comes 2nd
–
Ex: AgCl = silver chloride
–
Ex: Ba3(PO4)2 = barium phosphate
II. NAMING IONIC COMPOUNDS:
1. Rules:
b) Ions with more than one charge, you have to
figure out the charge and use the correct
roman numerals!
•
Always use the anions charge to figure
out the correct cation
II. NAMING IONIC COMPOUNDS:
Ex: FeO
Determine the charge of the anion (neg. ion)
-2
Oxide’s charge is ____
So Fe has to have a +2 charge because FeO
is a NEUTRAL compound!
-2
O
Ions have to be: ____ and _____
Iron II oxide
So it is ________________
Fe+2
II. NAMING IONIC COMPOUNDS:
Ex:Cr2(SO4)3
Determine the charge of the anion (neg. ion)
-2
Sulfate's charge is ____
and you have 3 ions for
-6 for the anions.
a total charge of _____
So the 2 Cr ions have to have a total charge of
+6 since Cr2(SO4)3 is a NEUTRAL compound.
___
II. NAMING IONIC COMPOUNDS:
Ex:Cr2(SO4)3
+3
-2
Cr
SO
Ions have to be: _____ and ____4
So it is__________________
Chromium III sulfate
III. WRITING MOLECULAR FORMULAS
1. Chemical formula for a
molecular compound is called
a molecular formula
IV. WRITING MOLECULAR FORMULAS
2. Molecular formula = formula showing
the types and numbers of atoms
combined in a single molecule of a
molecular compound
Molecular compounds are usually 2
nonmetals
III. WRITING MOLECULAR FORMULAS
3. Prefixes tell you what the subscript
will be!
Ex: Carbon monoxide
Ex: Carbon dioxide
CO
CO2
Ex: Dinitrogen trioxide
N2O3
III. WRITING MOLECULAR FORMULAS
Prefixes:
1
Mono2
Di3
Tri4
Tetra5
Penta-
6
7
8
9
10
HexaHeptaOctaNonDeca-
IV. NAMING MOLECULAR COMPOUNDS
1. Rules for naming molecular compounds:
a. A prefix is used with the name of the
FIRST element ONLY if there is more
than one atom of that element is present.
b. The second element is named by
combining a prefix and changing the
ending to -ide
IV. NAMING MOLECULAR COMPOUNDS
Ex: NO is called nitrogen monoxide
Ex: N20 is called dinitrogen monoxide
IV. NAMING MOLECULAR COMPOUNDS
2. Hints to use when molecular and ionic
compounds are on the same
worksheet/test:
Determine if the compound is molecular
or ionic.
Molecular compounds ONLY contain
NONMETALS.
IV. NAMING MOLECULAR COMPOUNDS
Ionic compounds ONLY contain METALS
and NONMETALS.
Compounds that contain ammonium ion
(NH4+) are IONIC compounds.
Remember that there is an ion
“dichromate”. So dichromate would be
part of an IONIC compound!