Name ____________________________________
Period ____________
Writing Formulas
1. How do chemists use Symbols, Formulas, and Equations?
a. Symbol- is a shorthand way of representing elements.
i. Element symbols have 1 or 2 letters.
ii. The first is capitalized the second lowercase
iii. Give some examples:
b. Formulas - are a shorthand way of representing compounds.
i. Each capitalized letter starts a different element.
ii. Subscripts (written after and below each element’s symbol) represent the number of each
atom in the compound.
iii. The number 1 is not written.
iv. Give some examples:
2. Why do elements form compounds?
a. The atom is made up of 3 subatomic particles:
i. Protons - are positive and are found in the nucleus
ii. Electrons - are negative and are found outside nucleus
iii. Neutrons - are neutral and are found in the nucleus
3. Ionic compounds
a. Atoms can gain or lose electrons but they usually don’t change the number of protons they have
i. Neutral atoms have equal numbers of protons and electrons
ii. Ions – atoms with a charge that have an unequal number of protons and
electrons
iii. When ions with opposite charges come close to each other they attract and stick to each
other like magnets and form ionic substances
1. If an atom gains electron(s) it will have a negative charge.
a. anions - The negative ion (more electrons than protons)
2. If an atom loses electron(s), it will have a positive charge.
a. cations - The positive ion (less electrons than protons)
3. Compounds formed from the combination of positive and negative ions are called
formula units or ionic compounds
1. What are the different types of ionic compounds?
a. There are two basic types of ionic compounds, binary ionic compounds and tertiary ionic
compounds
b. Binary Ionic compounds – Ionic compounds that consist of one cation and one anion
i. The anions and cations in a binary ionic compound can have different charges, but they
always bond together to make a neutral compound
Examples of How Ionic Compounds form:
+1
Na
Mg +2
B +3
N -3
Na3N
Mg3N2
BN
O -2
Na2O
MgO
B2O3
F -1
NaF
MgF2
BF3
Anions and cations always come together to make neutral compounds
c. Tertiary ionic compounds - Ionic compounds that consist of polyatomic ions
i. Polyatomic ions - a group of atoms that come together to form a molecule with a single
charge
Examples of How tertiary ionic compounds form:
+1
NH4
Mg +2
B +3
PO4 -3
(NH4)3PO4
Mg3(PO4)2
BPO4
SO4 -2
(NH4)2SO4
MgSO4
B2(SO4)3
OH -1
NH4OH
Mg(OH)2
B(OH)3
Polyatomic Anions and cations always come together to make neutral compounds
1) How do you go from a name to a formula with ionic compounds?
a) First determine if it an ionic or covalent compound:
i) If it is an ionic compound then the name will not include any prefixes (mono-, di-, tri- ect.)
ii) If it a covalent compound then the name will include prefixes
iii) If there is a polyatomic anion present than it is an ionic compound
b) Write the formula for the positive portion of the ion with its charge
i) The positive portion of the ion is always the first element(s)
ii) The charge of a polyvalent metal is always indicated by roman numerals
c) Wright the formula for the negative portion of the ion with its charge
i) The negative portion of the ion is always the second element(s)
ii) If the negative portion ends in -ide it is usually just an element. Hidroxide (OH-) is an exception
d) Determine the lowest whole number ratio of positive stuff to negative stuff that makes the compound
neutral
Write the formula of for the following ionic compounds:
Nickle (II) hydroxide
Potassium nitrate
magnesium sulfite
ammonium chloride
sodium floride
2) How do you go from a formula to a name with an ionic compound?
a) First check to see if it is a covalent compound be seeing if it is a metal bound to a nonmetal or two non
metals bound together
i) If it is two non metals then it is probably covalent
ii) If it is metal bound to a non metal than it is ionic
iii) If there is a polyatomic anion involved then it is ionic
b) Name the positive portion of the ion first
c) Name the negative portion of the ion second
d) Write the charge of any polyvalent metal in roman numerals after its name
i) If the positive portion is a polyvalent metal then you must determine the charge by looking at the
negative component of the ion and determining its charge by assuming that the ion is neutral
Write the formula of for the following ionic compounds:
Ni(OH)2
KNO3
MgSO3
NH4Cl
NaF
a) Polyvalent Metals - Some metals including the transition metals can have more than one
charge or oxidation state
i) This is because they have d orbitals that can become stable in a number of different ways
ii) The only way to determine the charge of the cation in a chemical formula is by looking at the charge
of the anion it is bound too and determining what the equal and opposite charge will be
iii) When writing out the name of the compound that contains a polyvalent metal the charge of the
polyvalent metal is distinguish by following it with a roman numeral
Iron can have a charge of +2 or +3 so in a ionic compound:
If the iron is Fe+2 it is written Iron (II) and is read as “iron two”
If the iron is Fe+3 it is written as Iron (III) and is read “iron three”
For example when Fe+2 is bound to two chlorines:
The formula would be FeCl2, and the name would be written Iron (II) chloride
When Fe+3 is bound to three chlorines:
The formula would be FeCl3, and the name would be written Iron (III) Chloride
What would be the formula for Copper (I) sulfate?
Cu2SO4
What is the name of the following compound, Cu3(PO4)2?
Copper (II) Phosphate
Write the formulas for the following compounds:
iron (II) chloride
________________
iron (II) sulfate
________________
iron (III) chloride
________________
iron (III) sulfate
________________
Cu3PO4
______________________
Cu3(PO4)2
______________________
Pb(NO3)4
______________________
Pb(NO3)2
______________________
Lithium hydroxide
________________
aluminum hydroxide ________________