SCIENCE 10
1. Use the periodic table and a list of ions to convert
names to formulas and formulas to names for :
a) simple ionic compounds
b) ionic compounds with multivalent metals
c) ionic compounds with polyatomic ions
2. Convert names to formulas and formulas to names
for covalent compounds, using prefixes up to “deca”
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Ionic compound
Covalent compound
Combining capacity
Ion
Attract
Repel
Valence electrons
Chemical bond
Simple ionic bond
Multivalent ions
Polyatomic ions
Molecules
• Ionic compounds are made up of positive and negative
ions.
– All of the positive and negative ions
organize in a pattern.
• Negative-positive attract.
• Negative-negative and positive-positive repel.
Salt, NaCl
See pages 184 - 185
– Ionic compounds form from the inside out as solid crystals.
– Ionic compounds are like a solid stack of bricks.
• A salt shaker contains thousands of small pieces of NaCl.
See pages 184 - 185
• Compounds are usually named to show what elements have
combined to make the compound.
• If a compound is formed from 2 elements then it is named by writing
the 2 elements and then changing the name of the second one to “ide”.
• E.g. ~ NaCl is named as Sodium chloride
• E.g. ~ KI is named as Potassium iodide
• E.g. ~ Al2O3 is named as Aluminum oxide
• E.g. ~ Si3N4 is named Silicon nitride
See pages 186 - 187
• STEP 1: identify the two elements
• STEP 2: always write the metallic element first.
• STEP 3: change the ending of the 2nd element to “ide”.
–
–
–
–
Magnesium bromide
MgBr2 =
Sodium chloride
NaCl =
Potassium oxide
K 2O =
CaCl2 =
Calcium chloride
See pages 186 - 187
The name of an ionic compound = positive ion + negative ion-ide.
–Example, what is the name of Ca3N2?
• Ca, the positive ion, is calcium.
• N, the negative ion, is nitrogen.
• Drop the end of the anion and add -ide.
• Calcium nitride
See pages 186 - 187
When atoms are held together in a compound, they are said
to be connected by a chemical bond.
To predict the formulas or atomic makeup of compounds, a
model can be used:
1. Imagine that atoms have
“hands”.
2. When atoms bond to form a
compound, they “hold hands”.
3. Every atom has a particular
number of “hands”, and this
number is known as the atoms’
combining capacity.
The +/- combining capacity for atoms can be found at the top right of the element square.
Atoms “hold hands” or bond
according to these rules:
1.In a compound, every “hand”
of an atom must be held by the
“hand” of another atom.
2.There are no “empty hands”.
3.The number of atoms required
to “hold hands” is the number of
atoms in the compound.
Example: Write the formula for Water
1.Water is made up of Hydrogen (H) and Oxygen (O).
2.Hydrogen has a combining capacity of +1, it has one “hand”.
3. Oxygen has a combining capacity of -2, it has two “hands”.
Example: Write the formula for Water
4.It takes two hydrogen atoms to hold both of the hands of
one oxygen atom.
STEP ONE: Write the symbol
for the more metallic element
first. Then, write the symbol for
the non-metallic element.
Calcium chloride
2
Ca
Cl
STEP TWO: Write the
combining capacities for the
elements. Ignore the + and –
charges. *If there is no #, the
combining capacity is 1.
Ca1Cl2
STEP THREE: Criss cross
the combining capacities to get
the subscripts.
CaCl2
1
REMEMBER: Subscripts indicate the number of atoms each element
has in that compound. *If the element has only one atom, then no
subscript is needed for that element.
STEP ONE: Write the symbol
for the more metallic element
first. Then, write the symbol for
the non-metallic element.
STEP TWO: Write the
combining capacities for the
elements. Ignore the + and –
charges. *If there is no #, the
combining capacity is 1.
STEP THREE: Criss cross the
combining capacities to get the
subscripts.
Lithium Nitride
Li
1
N
3
Li3N1
Li3N
REMEMBER: Subscripts indicate the number of atoms each element
has in that compound. *If the element has only one atom, then no
subscript is needed for that element.
STEP ONE: Write the symbol
for the more metallic element
first. Then, write the symbol for
the non-metallic element.
STEP TWO: Write the
combining capacities for the
elements. Ignore the + and –
charges. *If there is no #, the
combining capacity is 1.
STEP THREE: Criss cross the
combining capacities to get the
subscripts.
Barium Sulphide
2
Ba
S
2
Ba2S2
BaS
REMEMBER: In an ionic compound, the positive charges balance out the
negative charges. The subscripts are always written in reduced form.
So, divide the subscripts by their lowest common denominator.
STEP ONE: Write the symbol for
the more metallic element first.
Then, write the symbol for the
non-metallic element.
STEP TWO: Write the combining
capacities for the elements.
Ignore the + and – charges. *If
there is no #, the combining
capacity is 1.
STEP THREE: Criss cross the
combining capacities to get the
subscripts.
Calcium carbide
2
Ca
C
4
Ca4C2
Ca2C
REMEMBER: In an ionic compound, the positive charges balance out
the negative charges. The subscripts are always written in reduced
form. So, divide the subscripts by their lowest common denominator.
• What is the formula for magnesium phosphide?
 magnesium is Mg2+ phosphorous is P3–
Calcium oxide, also
2+
3–
known as “quicklime”
 Need 3 Mg ions and 2 P ions
was once produced
by cooking limestone
in ancient kilns.
 Mg3P2
• Try the formula for calcium oxide.
 calcium is Ca2+ oxygen is O2–
 Need 1 Ca2+ ion and 1 O2– ions
 Ca2O2, which is simplified and
See page 188
written as CaO
Some elements have more than one combining capacity
(MULTIVALENT), so elements can combine in more than
one way. The most common c.c. is listed on top.
Iron can have a combining capacity of 2 or 3:
Example 1: Sometimes when iron combines
with oxygen, it can act like it has a combining
capacity of 2 and form a black compound
(FeO = Iron II oxide)
Example 2: Sometimes when iron combines
with oxygen, it can act like it has a combining
capacity of 3 and form a rust-coloured
compound
(Fe2O3 = Iron III oxide)
See pages 189 - 191
If an atom has only one possible combining capacity (like sodium, zinc,
or aluminum), a roman numeral is not written after its name.
NaCl
E.g. Sodium Chloride =
ZnS
E.g. Zinc Sulphide =
Al2O3
E.g. Aluminum oxide =
A roman numeral is written after the name of an element with more than
one combining capacity so that chemists know which form of the
element we are dealing with.
E.g. Iron II chloride = FeCl2
E.g. Copper I oxide = Cu2O
E.g. Nickel III bromide = NiBr3
See pages 189 - 191
E.g. Titanium IV oxide = TiO
It is easy to write the formulas for multivalent ionic compounds,
because they tell you their combining capacities so you don’t
need to look on the periodic table.
Example:
1.Gold (I) chloride: Au+1 Cl-1
AuCl
2.Iron (III) sulphide: Fe+3S-2
Fe2S3
3.Lead (IV) oxide: Pb+4O-2
Pb2O4
PbO2
See pages 189 - 191
It is a little more difficult to name a multivalent ionic compound, because you
have to work backwards to figure out which combining capacity was used.
Remember to use a ROMAN NUMERAL!!!
Example:
1.SnCl2
1. Sn = tin
Sn1 Cl 2
Cl = chloride
2. Combining capacity of tin is either 4 or +2
3. Combining capacity of chlorine is -1
4. Reverse the combining capacities to
figure out which combining capacity
was used.
5. Ask yourself, is “2” an option? If the
answer is yes, you can name the
compound:
Tin (II) chloride
Example:
1.PbO
2
Pb1
1. Pb = lead
2
O1
O = oxide
2. Combining capacity of lead is +2 or +4
3. Combining capacity of oxygen is -2
4. Reverse the combining capacities to
figure out which combining capacity
was used.
5. Ask yourself “is 1 an option?”
6. If the answer is “no”, then check if the
numbers were reduced. In this case,oxygen
is 2, and if it has been reduced to “1”, then
both subscripts must have been divided by 2.
7. So, do the opposite and multiply by 2.
8. Now you can name the compound:
Lead (II) oxide
Example:
1.CuCl2
1. Cu = copper
Cu1 Cl 2
Cl = chloride
2. Combining capacity of copper is +1 or
+2
3. Combining capacity of chlorine is -1
4. Reverse the combining capacities to
figure out which combining
capacity was used.
5. Ask yourself “is 2 an option?”
6. If the answer is “yes”, then you can
name the compound:
Copper (II) chloride
 Write the formula for Manganese (III) sulfide.
 This manganese is Mn3+
sulfur is S2–
 Mn2S3
 Write the name for TiF4
 titanium is Ti4+ or Ti3+
 1 Ti4+ ion and 4 F– ions
 titanium (IV) fluoride
fluorine is F–
See pages 189 - 191
• Some ions, called polyatomic ions, are made
up of several atoms joined together with
covalent bonds.
– The whole group has a + or – charge, not the
individual atoms.
See pages 192 - 193
The groups of atoms have their own combining capacity that should be used when
writing chemical formulas.
USE BRACKETS AROUND THE POLYATOMIC IONS!!
Example: Compound formed with Na and CO3 would be…
Example: Compound formed between Ca and OH would be…
+1
-2
Na (CO3)
+2
-1
Ca (OH)
Na 2(CO3)
Ca(OH)2
See pages 192 - 193
When you are naming compounds with more than two elements, you are
dealing with a polyatomic ion. All you need to do, is find it in the chart so
you can name your compound.
1.If the polyatomic ion group has a positive charge (+) it acts like a metal
and comes first in the name.
2.If the polyatomic ion group has a negative charge (-) it acts like a nonmetal and comes second in the name.
Example:
Na2 CO3 = 3 different elements
Does Sodium carbon oxide sound right? No!!
You must have a polyatomic ion. See chart.
Name: sodium carbonate
See pages 192 - 193
Example 2:
Ca (OH)2 = 3 different elements
Does calcium oxygen hydride sound right? No!!
You must have a polyatomic ion. See chart.
Name: Calcium hydroxide
Example 3:
NaNO3 = 3 different elements
Does Sodium nitrogen oxide sound right? No!!
You must have a polyatomic ion. See chart!
Name: Sodium Nitrate
Example 4:
NH4Cl = 4 different elements
Does Nitrogen hydrogen chloride sound right? No!!
You must have a polyatomic ion. See chart!
Name: ammonium chloride
See pages 192 - 193
 What is the formula of sodium sulphate?
Na+ and SO42–
Na2SO4
 What is the name of the compound KClO?
K+ = potassium ClO– =
hypochlorite
potassium hypochlorite
• Covalent molecules share electrons.
 Covalent bonds occur between two or more
non-metals.
 These molecules exist as solids, liquids or gases.
 Covalent molecules are like a play-pit full of
plastic balls.
 Each plastic ball =
1 covalent molecule of H2O
Water, H2O
See pages 184 - 185
• The chemical formula of a covalent compound tells us the number of
each element in the compound.
– Sometimes the names don’t tell us what elements make up the compounds.
– Subscripts mean something different in covalent compounds
• Ionic compounds subscripts show the smallest
whole-number ratio between the ions in the compound.
• Covalent molecules have subscripts that show the actual number of
atoms in the molecule.
Water: H2O
Hydrogen Peroxide: H2O2
See page 193
Methane: CH4
 What is the chemical formula for the molecule ethanol?
 C2H6O, a name that must be memorized or looked up when needed.
 What is the chemical formula for candle wax?
 C25H52
 What is the name of the molecule C12O22H11?
 Sucrose, also called table sugar.
See page 193
• Covalent compounds with 2 non-metal
atoms use a system of prefixes.
 Prefixes are often used before the atom name to
indicate the number of atoms in the molecule.
 Example:
 CO = carbon monoxide
 CO2 = carbon dioxide
 CCl4 = carbon tetrachloride
See pages 194 - 195
 STEP 1: Write the most metallic atom (farthest
left) first
 STEP 2: Use prefixes to symbolize the # of
each atom.
 STEP 3: Add -ide to the end of the second
atom’s name
See pages 194 - 195
 What is the chemical formula for the molecule
trinitrogen tetrachloride?
 N3Cl4
 What is the name of the molecule Si3P6?
 Trisilicon hexaphosphide
See pages 194 - 195
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To determine whether a compound is ionic or covalent:
1. Examine the formula.
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Does it start with a metal?
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Does it start with the ammonium ion (NH4)?
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It must be an Ionic compound.
It must be an ionic compound with a polyatomic
ion.
Does it start with a non-metal?
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It must be a covalent compound.
See pages 196 - 197
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To determine whether a compound is ionic or covalent:
2.
If the compound is ionic:
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•
•
•
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Check the metal to see if it has more than 2 combining capacities.
It is does, follow the rules for a multivalent ionic compound. Don’t
forget the Roman numerals when naming.
Check to see if there are more than 2 elements in the compound.
If there are, follow the rules for a polyatomic ionic compound.
Don’t forget the brackets when writing the formula!
Naming starts with the name of the metal atom (positive ion).
If it ends with a single non-metal, naming will just end in -ide.
If it ends in a polyatomic ion, look up the name/formula.
See pages 196 - 197
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To determine whether a compound is ionic or covalent:
3.
If the compound is covalent:
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Use the prefix system of naming
If there are more than two different non-metal elements, or it starts
with H, there is probably a different name for the covalent
molecule.
See pages 196 - 197