WRITING AND NAMING IONIC COMPOUNDS

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WRITING AND NAMING IONIC COMPOUNDS
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When atoms combine, its always in simple whole
number ratios
The smallest unit of atomic combinations that
retains the characteristics of the compound is a
molecule
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The composition of a molecule can be represented
in two ways as either an empirical formula or a
molecular formula
CH2
C3H6
An empirical formula gives the simplest ratio of
atoms in a compound
A molecular formula tells how many of each atom
are present in the compound
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A remarkable feature of compounds formed from
elements is that the properties of the reactant
elements are lost.

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In order to become more stable an some atoms find
it energetically fea-sible to either lose or gain
valence electrons.
Atoms that lose e- are positive A.K.A. cation
Atoms that gain e- are negative A.K.A. anion
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We tend to focus specifically on the loss or gain
of the outer s, p, (A.K.A. valence e-) ,and
sometimes the d e- of unfilled d sublevels).
The valence e- an atom contains has a direct
effect on the charge the atom develops as it
forms an ionic bond.
We have a list of the common ionic charges
developed during ionic bonding.
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SOME COMMON CATIONS (Note the names of many of
the ions include Roman numerals.
These numerals are
known as the Stock system of naming chemical ions
and elements)
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2
3
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Lead (II)
Pb2
Mn2
Manganese (II)
MONATOMIC IONS
Mercury (II)
Hg2
Nickel (II)
Ni2
Tin (II)
Sn2
Vanadium (II)
V2
Zinc
Zn2
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SOME COMMON ANIONS (Note the names of many of
the ions include Roman numerals.
These numerals are
known as the Stock system of naming chemical ions
and elements)
-1
-2
-3
-4
MONATOMIC IONS
Nitride
N-3
Fluoride
Oxide
O-2
F-1
S-2
Chloride
Cl-1
Sulfide
Phosphide
P-3
Bromide
Br-1
Iodide
I-1
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There are also combinations of covalently bonded
atoms that also have a charge called polyatomic
ions
Poly- means many, but we treat each of these
polyatomic ions as a single unit with a single
charge
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POLYATOMIC IONS
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POLYATOMIC IONS
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Today is all about combining these electrically
charged ions together to form stable compounds.
Reminder when two atoms combine transferring
valence electrons it is called an ionic bond.
Oppositely charged ions attract each other and
form an ionic bond that is electrically neutral,
to establish a molecule that is neutral.
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Looking at the structure of salt shows that the
attraction between ions is so great that many
sodium ions and chloride ions become involved.
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The results of each ion being surrounded by
several other ions allows the attraction between
oppositely charged ions to be much greater than
the repulsion between ions with the same charge.
The strong attraction between the ions, the
orderly arrangement in the crystal affect the
properties of the compound.
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Cations anions are pulled together in a tightly
packed structure, giving each crystal a
characteristic shape
The simplest repeating unit of anions and cations
is called a unit cell.
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Predicting the formation of ionic compounds.
We can predict the combinations of ions and the
formation of their ionic formulas, knowing how
ions interact
We can have 2 different kinds of ionic compounds
formed binary or ternary
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WRITING IONIC FORMULAS
There are a couple of rules to follow to make
sure that the proper ionic formula is written.
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RULE 1
Ions will combine only in the simplest whole
number ratio which cancels out the charge to form
a neutral compound
The sum of the ions charges must be zero
3(1) (-3) 0
2 (-2) 0
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RULE 2
The compound formula is ALWAYS written with the
cation first then the anion.
Its better to be positive than negative ?
NaCl
ClNa
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Some ionic compounds charges automatically
cancel each other out.
KI
MgO
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What if we were forming ionic compounds with ions
whose charges dont add up to a charge of 0?
How do we decide the proper ratio of cations and
anions?
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What if we had three chlorine ions for every one
Aluminum ion?
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We need to find the ratio of ions that will make
the charges cancel out to a neutral compound.
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We have a trick that will help us know the number
of the ions to make a neutral compound.
ITS NOT A TRICK SO MUCH AS A SHORTCUT!
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CRISS-CROSS RULE
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Using polyatomic ions
To write the formulas for compounds containing
polyatomic ions, follow the rules for writing
formulas for binary compounds, with one
additional consideration.
We add parentheses around the polyatomic ion when
more than one of the ion is needed to develop the
proper ratio.
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Practice Writing Formulas
CaO
Sn(CO3)2
(NH4)2SO4
Mg(C2H3O2)2
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NAMING THEM
Most of the time you can name an ionic compound
by 1) Writing the name of the first element 2)
Writing the root of the name of the second
element 3) Adding -ide to the root
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NAMING THEM
CaCl2 ? K3P ? Al2S3 ?
Calcium chloride
Potassium phosphide
Aluminum sulfide
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NAMING THEM
Some of our metals have more than one ionic charge

• We have to determine the charge on the metal
• We then indicate the charge as a roman numeral

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NAMING THEM
FeCl2 ? FeCl3 ? PbBr2 ?
Iron(II) chloride
Iron (III) chloride
Lead (II) bromide
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NAMING THEM
If the compound has a polyatomic ion in it
1) name the first element, including the roman
numeral if appropriate 2) then name the
polyatomic ion
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NAMING THEM
Fe(OH)2 ? Ca3 (PO4)2 ? Na2SO4 ?
Iron(II) hydroxide
Calcium phosphate
Sodium sulfate
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Strontium Nitrite ?
Sr(NO2)2
CuOH ?
Copper (I) hydroxide
Lead (IV) phosphide ?
Pb3P4
NH4OH ?
Ammonium hydroxide
Sodium carbonate ?
Na2CO3