Section 2.3—Chemical
Formulas
We need to be able to read the formulas for chemicals in
the antacids!
Reminders from Section 2.2
Your Appendix (Page A-2) has lists of:
Common polyatomic ions
Multivalent metals
Covalent prefixes
Use your periodic table to determine the
charges of common elements when they
form ions
Binary Ionic compounds
Definitions
Ionic bond- bond formed by attraction
between + and - ions
Binary Ionic Compound- compound
containing two elements—one metal
and one non-metal
+
Cation
Anion
Ionic Compound
Metals & Non-Metals
Ionic Bonds are between metals & non-metals
H
He
Li
Be
B
C
N
O
F
Ne
Na
Mg
Al
Si
P
S
Cl
Ar
K
Ca
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
Ga
Ge
As
Se
Br
Kr
Rb
Sr
Y
Zr
Nb
Mo
Tc
Ru
Rh
Pd
Ag
Cd
In
Sn
Sb
Te
I
Xe
Cs
Ba
Lu
Hf
Ta
W
Re
Os
Ir
Pt
Au
Hg
Tl
Pb
Bi
Po
At
Rn
Fr
Ra
Lr
Rf
Db
Sg
Bh
Hs
Mt
Uun
Uuu
Uub
Uut
Metals
Metalloids
Nonmetals
Identifying & Naming Binary Ionic
 These compounds:
End in “-ide” (except “hydroxide and cyanide”)
Do NOT contain covalent prefixes
 To write these formulas:
Write the symbol & charge of the first element (the metal,
cation)
Write the symbol & charge of the second element (the
non-metal, anion)
Add more of the cations and/or anions to have a neutral
compound
Use subscripts to show how many of each type of ion is
there.
Example #1
Sodium chloride
Example #1
Na+1
Cation
Sodium chloride
Anion
Cl-1
NaCl
Example #1
Na+1
Cation
Na+1Cl-1
Sodium chloride
Anion
Cl-1
NaCl
+1 + -1 = 0
The compound is neutral…no
subscripts are needed.
Example #2
Calcium bromide
Example #2
Ca+2
Cation
Calcium bromide
Anion
Br-1
Example #2
Ca+2
Cation
Ca+2Br-1
Calcium bromide
Anion
Br-1
CaBr2
+2 + -1 = +1
Ca+2Br-1Br-1
+2 + -1 + -1 = 0
The subscript “2” is used to show
that 2 anions are needed.
Let’s Practice
Cesium chloride
Example:
Write the
following
chemical
formulas
Potassium oxide
Calcium sulfide
Lithium nitride
Let’s Practice
Example:
Write the
following
chemical
formulas
Cesium chloride
CsCl
Potassium oxide
K2O
Calcium sulfide
CaS
Lithium nitride
Li3N
Polyatomic Ionic Compounds
Definition
Polyatomic Ion- more than one atom
that together have a charge
Polyatomic Ionic Compoundcompound containing at least one
polyatomic ion
+
Cation
Polyatomic
Anion
Polyatomic Ionic
Compound
Identifying & Naming Polyatomic Ionic
 These compounds:
Do not end with “-ide” (except hydroxide & cyanide)
Do not use covalent prefixes
 To write these formulas:
Write the symbol & charge of the cation & anion
Add additional cations or anions to have a neutral
compound
Use subscripts to show the number of ions
 When using subscripts with a polyatomic ion, you must put
the polyatomic ion in parenthesis.
Example #3
Sodium carbonate
Example #3
Na+1
Cation
Sodium carbonate
Polyatomic
Anion
CO3-2
Example #3
Na+1
Cation
Na+CO32-
Sodium carbonate
Polyatomic
Anion
CO3-2
Na2CO3
+1 + -2 = -1
Na+Na+CO32+1 + 1 + -2 = 0
The subscript “2” is used to show
that 2 cations are needed.
Example #4
Magnesium nitrate
Example #4
Mg+2
Cation
Magnesium nitrate
Polyatomic
Anion
NO3-1
Example #4
Mg+2
Mg+2NO3-
Cation
+2 + -1 = 1
Magnesium nitrate
Mg+2NO3- NO3-
Polyatomic
Anion
+2 + -1 + -1 = 0
NO3-1
Mg(NO3)2
The subscript “2” is used to show
that 2 anions are needed.
Use parenthesis when adding
subscripts to polyatomic ions
Let’s Practice
Sodium nitrate
Example:
Write the
following
chemical
formulas
Calcium chlorate
Potassium sulfite
Calcium hydroxide
Let’s Practice
Example:
Write the
following
chemical
formulas
Sodium nitrate
NaNO3
Calcium chlorate
Ca(ClO3)2
Potassium sulfite
K2SO3
Calcium hydroxide
Ca(OH)2
Multivalent Metals
Definition
Multivalent Metal- metal that has more
than one possibility for cationic charge
Identifying & Naming Multivalent Metals
These compounds:
Will have roman numerals
To write these formulas:
Same as binary ionic or polyatomic ionic.
The roman numerals tell the charge of the
metal (cation)
Example #5
Iron (III) oxide
Example #5
Fe+3
Cation
Iron (III) oxide
Anion
O-2
Example #5
Fe+3
Fe+3O2-
Cation
+3 + -2 = -1
Iron (III) oxide
Fe+3Fe+3O2-O2-
Anion
+3 + 3 + -2 + -2 + -2 = 0
O-2
Fe2O3
The subscript “2” and “3” are used
to show the numbers of atoms
needed.
Example #6
Copper (II) nitrate
Example #6
Cu+2
Cation
Copper (II) nitrate
Polyatomic
Anion
NO3-1
Example #6
Cu+2
Cu+2NO3-
Cation
+2 + -1 = 1
Copper (II) nitrate
Cu+2NO3-NO3-
Polyatomic
Anion
+2 + -1 + -1 = 0
NO3-1
Cu(NO3)2
Use parenthesis when adding
subscripts to a polyatomic ion
Let’s Practice
Iron (II) nitrate
Example:
Write the
following
chemical
formulas
Copper (I) chloride
Lead (IV) hydroxide
Tin (II) oxide
Let’s Practice
Example:
Write the
following
chemical
formulas
Iron (II) nitrate
Fe(NO3)2
Copper (I) chloride
CuCl
Lead (IV) hydroxide
Pb(OH)4
Tin (II) oxide
SnO
Binary Covalent Compounds
Definition
Covalent bond atoms share electrons
Binary Covalent Compound
compound made from two non-metals
that share electrons
Non
metal
Non
metal
Covalent compound
Identifying & Naming Binary Covalent
These compounds:
Use covalent prefixes
To write these formulas:
Write the symbols of the first and second
element
Use the covalent prefixes (assume the first
element is “1” if there’s no prefix) as the
subscripts to show number of atoms.
Atoms do not form charges when bonding covalently…you DO NOT
need to worry about charges with this type!
Example #7
Dinitrogen Tetraoxide
Example #7
“Di-” = 2
N
Dinitrogen Tetraoxide
O
“Tetra-” = 4
N2O4
Example #8
Silicon dioxide
Example #8
“Mono-” is not written for
the first element
Si
Silicon dioxide
O
“Di-” = 2
SiO2
CAUTION!!!
“di” and “bi” do not mean the same thing!
di-
bi-
Stands for “2” in covalent
compounds
Means there’s a hydrogen in
the polyatomic anion
Carbon dioxide = CO2
Sodium biphosphate =
Na2HPO4
Let’s Practice
Carbon monoxide
Example:
Write the
following
chemical
formulas
Nitrogen dioxide
Diphosphorus pentaoxide
Let’s Practice
Example:
Write the
following
chemical
formulas
Carbon monoxide
CO
Nitrogen dioxide
NO2
Diphosphorus pentaoxide
P2O5
Nomenclature Summary
Writing Chemical
Formulas
Does not contain
covalent prefixes
Ends with “-ide”
(except hydroxide &
cyanide) = Binary Ionic
Does contain covalent
prefixes = Binary
Covalent compound
All others = Polyatomic
Ionic
Mixed Practice
Magnesium hydroxide
Example:
Write the
following
chemical
formulas
Copper (II) nitrate
Iron (III) oxide
Nitrogen dioxide
Sodium bicarbonate
Mixed Practice
Example:
Write the
following
chemical
formulas
Magnesium hydroxide
Mg(OH)2
Copper (II) nitrate
Cu(NO3)2
Iron (III) oxide
Fe2O3
Nitrogen dioxide
NO2
Sodium bicarbonate
NaHCO3