Chemistry 10
Naming Compounds and Writing Formulas [Section 1]
Ionic Compounds
- Polyatomic ions = compounds w/ ionic charges.
- can bond to other ions to form ionic compounds
Naming Polyatomic/Ionic compounds
1. Name the positive ion first
2. Name the negative ion second.
3. If either ion is polyatomic, simply use the name of the polyatomic ion.
(DO NOT change the ending of the name)
Steps for writing Iron (III) hydroxide Ammonium Sodium
the formula Carbonate Phosphite
1: identify each ion Fe3+, OH- NH4+, Co32- Na+, PO33-
and its charge (Cancellation, 4+ =
2+, Co32- = Co3-)
2: determine the Fe = 3+ NH = 2+ PO33 = 3-
total charges -1 + -1 + -1 = -3 Co3 Na + Na + Na = 3+
needed to balance OH, OH, OH = 3- + Co3 = 2- 3 Sodium for every
+ w/ - 1 iron for every 3 2 Ammonium for 1 Phosphite
hydroxide every 1 Carbonate
3: note the ratio of 1 Fe for every 3 OH 2 NH4+ ions for 3 Na for every 1
positive ions to ions every Co32- ion PO33 ion.
negative ions.
4: use subscripts FeOH3 = X NH42 Co3 = X NaPO3 = X
and brackets to
write the formula. Fe(OH)3 = ✓ (NH4)2 CO3 = ✓ Na3PO3 = ✓
Omit brackets if
only one ion is *(if you write the first *(if you write the first *(if you write the first
needed. one, only H has 3-) one, there are 42 H’s) one, there’s only 1 Na,
when there's
supposed to be 3)
1
, Chemistry 10
Why does Iron (III) Hydroxide have roman numerals?
- On the periodic table, Iron has 2 electron charges.
- 2+ & 3+
- In Iron (III) Hydroxide, they use the 3+ Charge.
- So, in Iron (II) Hydroxide, they use the 2+ Charge.
When atoms on the periodic table have more than one charge, the charge that is
used it represented in the written form of the element with roman numerals
*This rule applies to ALL electrons with 2 or more charges.
Crossover rule /Method
- A shortcut to help you determine the formula of an ionic compound. Follow
the steps below to figure out how to use the crossover method
1. Write the formulas of the ions beside each other.
2. Cross over the magnitude (amount or size) of the charge on the cation
(positive ion) so that it is the subscript for the anion (negative ion).
3. Cross over the magnitude of the charge on the anion so that it is the subscript
for the cation.
4. Reduce to lowest terms if necessary.
5. Double-check your formula.
EX: Magnesium Chloride EX: Calcium Oxide
2
, Chemistry 10
Covalent Compounds
Naming Covalent Compounds using the prefix system
- Use the following prefix-naming system where the prefix tells you the number
of atoms of the element that are involved in the compound
Mono = 1
Di = 2
Tri = 3
Tetra = 4
Penta = 5
Hexa = 6
Hepta= 7
Octa= 8
Nona = 9
Deca = 10
- Just name the compound like you would do for an ionic compound but make
sure you place a prefix of each non-metal element to show the number of
atoms that are present.
- (you can omit the mono prefix in front of the first non-metal element
only)
1. N2S5 dinitrogen pentasulfide
2. CCl4 carbon tetrachloride
3. CO2 carbon dioxide
4. CO carbon monoxide
3
Naming Compounds and Writing Formulas [Section 1]
Ionic Compounds
- Polyatomic ions = compounds w/ ionic charges.
- can bond to other ions to form ionic compounds
Naming Polyatomic/Ionic compounds
1. Name the positive ion first
2. Name the negative ion second.
3. If either ion is polyatomic, simply use the name of the polyatomic ion.
(DO NOT change the ending of the name)
Steps for writing Iron (III) hydroxide Ammonium Sodium
the formula Carbonate Phosphite
1: identify each ion Fe3+, OH- NH4+, Co32- Na+, PO33-
and its charge (Cancellation, 4+ =
2+, Co32- = Co3-)
2: determine the Fe = 3+ NH = 2+ PO33 = 3-
total charges -1 + -1 + -1 = -3 Co3 Na + Na + Na = 3+
needed to balance OH, OH, OH = 3- + Co3 = 2- 3 Sodium for every
+ w/ - 1 iron for every 3 2 Ammonium for 1 Phosphite
hydroxide every 1 Carbonate
3: note the ratio of 1 Fe for every 3 OH 2 NH4+ ions for 3 Na for every 1
positive ions to ions every Co32- ion PO33 ion.
negative ions.
4: use subscripts FeOH3 = X NH42 Co3 = X NaPO3 = X
and brackets to
write the formula. Fe(OH)3 = ✓ (NH4)2 CO3 = ✓ Na3PO3 = ✓
Omit brackets if
only one ion is *(if you write the first *(if you write the first *(if you write the first
needed. one, only H has 3-) one, there are 42 H’s) one, there’s only 1 Na,
when there's
supposed to be 3)
1
, Chemistry 10
Why does Iron (III) Hydroxide have roman numerals?
- On the periodic table, Iron has 2 electron charges.
- 2+ & 3+
- In Iron (III) Hydroxide, they use the 3+ Charge.
- So, in Iron (II) Hydroxide, they use the 2+ Charge.
When atoms on the periodic table have more than one charge, the charge that is
used it represented in the written form of the element with roman numerals
*This rule applies to ALL electrons with 2 or more charges.
Crossover rule /Method
- A shortcut to help you determine the formula of an ionic compound. Follow
the steps below to figure out how to use the crossover method
1. Write the formulas of the ions beside each other.
2. Cross over the magnitude (amount or size) of the charge on the cation
(positive ion) so that it is the subscript for the anion (negative ion).
3. Cross over the magnitude of the charge on the anion so that it is the subscript
for the cation.
4. Reduce to lowest terms if necessary.
5. Double-check your formula.
EX: Magnesium Chloride EX: Calcium Oxide
2
, Chemistry 10
Covalent Compounds
Naming Covalent Compounds using the prefix system
- Use the following prefix-naming system where the prefix tells you the number
of atoms of the element that are involved in the compound
Mono = 1
Di = 2
Tri = 3
Tetra = 4
Penta = 5
Hexa = 6
Hepta= 7
Octa= 8
Nona = 9
Deca = 10
- Just name the compound like you would do for an ionic compound but make
sure you place a prefix of each non-metal element to show the number of
atoms that are present.
- (you can omit the mono prefix in front of the first non-metal element
only)
1. N2S5 dinitrogen pentasulfide
2. CCl4 carbon tetrachloride
3. CO2 carbon dioxide
4. CO carbon monoxide
3
