Concept 2 Notes - Ionic Bonds

Ionic Compounds

• Ionic compounds: made of positive and negative ions that chemically bond in a way that the charges equal out.
• Made of ions = charged atoms
• Cations = positively charged from losing electrons (typically metals)
• Anions = negatively charged from gaining electrons (typically nonmetals)
• Ionic bonds are formed when e- are transferred from the atom with the lower electronegativity to the higher.
• Electronegativity = ability of an atom to attract e- in a bond

Ion Examples:

Example: What ion will Lithium form?

Ion Examples:

Example: What ion will Nitrogen form?

Ions

• Elements in the same group have the same number of valence e-
• Because of this, elements in the same group tend to form ions the same way
• Ex. All elements in group 1 have 1 valence electron, so all of them will lose 1 e- to be stable, therefore forming an ion with a 1+ charge.

Will form Li1+

Will form Na1+

Will form K1+

Oxidation Numbers

• Oxidation numbers: the charge of an ion within a compound
• Written as a superscript to the right of the symbol
• Group 1 elements have 1 valence e-  1+ charge
• Group 2 elements have 2 valence e-  2+ charge

Skip groups 3-12 transition metals

• Group 13 elements have 3 valence e-  3+ charge
• Group 14 elements have 4 valence e-  4+/- charge
• Group 15 elements have 5 valence e-  3- charge
• Group 16 elements have 6 valence e-  2- charge
• Group 17 elements have 7 valence e-  1- charge

Rule of Zero Charge

• The charges of metal cations and nonmetal anions should always add up to zero.
• This makes the overall compound neutral with no charge.

AlCl3

Using Lewis Structures to show Bond Formation

1. Draw the Lewis structures for the individual elements.
2. Transfer e- (using an arrow) from the metal to nonmetal.
3. Add elements as needed. Continue transferring until all atoms are stable.
4. Draw the new Lewis structures after e- have been transferred showing the charges of the atoms.
5. Write the chemical formula using subscripts to show how many of each element were needed.
6. Double check that the overall charge is 0.

Using Lewis Structures to show Bond Formation

Example: What compound will form between Magnesium and Bromine?

Br

Br

Mg

Mg2+

Br

Br

Using Lewis Structures to show Bond Formation

Example: What compound will form between Aluminum and Oxygen?

3+

2-

Al

Al

3+

Al

2-

Al

2-

Practice Time!

Use Lewis structures to write chemical formulas for the following combination of elements:

1. Aluminum and Nitrogen
2. Strontium and Fluorine
3. Magnesium and Phosphorus

Nomenclature

• All compounds have chemical formulas and names.
• Different types of compounds follow different naming “rules”.
• Binary ionic compounds
• Compounds made of 2 elements that transfer e- in an ionic bond
• Compounds with polyatomic ions
• Polyatomic ion: a charged group of covalently bonded atoms
• Binary molecular compounds
• Compounds made of 2 elements that share e- in a covalent bond

How to determine the Chemical Formula for a Binary Ionic Compound

Name  Formula

1. Write down the ions of each element with charges.

(aka, the symbol with its oxidation #)

1. Determine the # of each ion it takes to make a compound with no charge.

(aka, “crisscross applesauce” the charges)

1. Write down the formula using subscripts to show how many of each ion it took.
2. Reduce/simplify (if needed).

How to determine the Chemical Formula for a Binary Ionic Compound

Name  Formula

Example: What is the formula for the compound that forms between calcium and nitrogen?

Ca 2+

N 3-

Ca3N2

Double check: 3(2+) + 2(3-) = 0

Practice Time!

Write the chemical formulas if the elements below formed compounds in notebook.

1. Aluminum and Chlorine
2. Lithium and Nitrogen
3. Magnesium and Fluorine
4. Calcium and Oxygen
5. Sodium and Sulfur

Naming Binary Ionic Compounds

Formula  Name

1. Write the name of the first element (the metal).
2. Write the name of the second element (the nonmetal) with an –ide ending.

Example: Name CaS.

Calcium sulfide

Practice Time!

Write the name of the binary ionic compounds based on the chemical formulas below. in notebook!

1. Be3N2
2. Na2O
3. K3P
4. AlN
5. MgCl2

Exceptions for Ionic Rules

Exception #1: Polyatomic Ions

• Polyatomic ions: a positively or negatively charged, covalently bonded group of atoms.

Naming Ionic Compounds w/ Polyatomic Ions

Formula  Name

1. Write the name of the first element (the metal).

Exception #1: If a polyatomic ion, use its special name.

1. Write the name of the second element (the nonmetal) with an –ide ending.

Exception #1: If a polyatomic ion, use its special name. No –ide ending added.

Examples: Na3PO4 MgSO4 NH4Cl

Sodium phosphate

Magnesium sulfate

Ammonium chloride

Practice Time!

Write the name of the ionic compounds based on the chemical formulas below. In notebook

1. NaNO3
2. CaSO4
3. (NH4)2O
4. Mg3(PO4)2
5. NH4NO3

How to determine the Chemical Formula for an Ionic Compound w/ Polyatomic Ions

Name  Formula

1. Write down the ions of each element with charges. (aka, the symbol with its oxidation #) (just keep the polyatomic ion in parentheses)
2. Determine the # of each ion it takes to make a compound with no charge. (aka, “crisscross applesauce” the charges) (keep subscripts outside of parentheses and don’t change ANYTHING inside)
3. Write down the formula using subscripts to show how many of each ion it took.
4. Reduce/simplify (if needed).

How to determine the Chemical Formula for an Ionic Compound w/ Polyatomic Ions

Name  Formula

Example: What is the formula for the compound calcium phosphate?

(PO4) 3-

Ca 2+

Ca3(PO4)2

Double check: 3(2+) + 2(3-) = 0

Practice Time!

Write the chemical formulas for the ionic compounds below. notebook

1. Barium sulfate
2. Aluminum carbonate
3. Calcium nitrate
4. Sodium acetate
5. Potassium phosphate

Exceptions for Ionic Rules

Exception #2: Transition Metals

• Transition metals: metals that “transition” because they can form many different ions
• Ex. Sodium is always Na1+ because it is in group 1 and group 1 metals have one valence e-  therefore they lose 1 e- to be stable.
• Iron as a transition metal can be Fe2+ or Fe3+
• Because you can’t determine the charge from the periodic table, a Roman Numeral is used to show it
• Ex. Copper (I)  Cu1+
• Ex. Copper (II)  Cu2+

Naming Ionic Compounds w/ Transition Metals

Formula  Name

1. Write the name of the first element (the metal).

Exception #2: If a transition metal, include a Roman numeral to indicate the charge of the metal.

1. Write the name of the second element (the nonmetal) with an –ide ending.

Examples: CuCl CuCl2

Copper (I) chloride

Copper (II) chloride

Determining the Roman Numeral

for Transition Metals

• Option 1 = Reverse crisscross
• Option 2 = Use visuals or math to determine what charge the cation must have for the overall charge to be 0.
• No matter what you choose, ALWAYS double check your work!

Sn3(PO4)4

Option 2:

Example:

3-

Option 1:

Sn?

(PO4)3-

3-

Tin (IV) phosphate

Sn3(PO4)4

3-

Tin (IV) phosphate

3(?) = +12

3-

4+

4(3-) = -12

Practice Time!

Write the name of the ionic compounds based on the chemical formulas below.

Iron (III) chloride

1. FeCl3
2. CrO
3. Mn2O7
4. Ag2S
5. CrN

Chromium (II) oxide

Manganese (VII) oxide

Silver (I) sulfide

Chromium (III) nitride

How to determine the Chemical Formula for an Ionic Compound w/ Transition Metals

Name  Formula

1. Write down the ions of each element with charges. (aka, the symbol with its oxidation #) (the transition metal’s charge will be given by the use of Roman numerals)
2. Determine the # of each ion it takes to make a compound with no charge. (aka, “crisscross applesauce” the charges)
3. Write down the formula using subscripts to show how many of each ion it took.
4. Reduce/simplify (if needed).

How to determine the Chemical Formula for an Ionic Compound w/ Transition Metals

Name  Formula

Example: What is the formula for the compound iron (II) oxide?

O 2-

Fe 2+

Fe2O2

FeO

Double check: 1(2+) + 1(2-) = 0

Practice Time!

Write the chemical formulas for the ionic compounds below.

1. Copper (II) sulfide
2. Iron (I) nitride
3. Titanium (IV) bromide
4. Manganese (IV) oxide
5. Chromium (VI) sulfide

SUMMARY: Naming Ionic Compounds

Formula  Name

1. Name the cation (metal).
2. Exception #1: If a polyatomic ion, use its special name.
3. Exception #2: If a transition metal, include a Roman numeral to indicate the charge of the metal.
4. Name the anion (nonmetal) with an –ide ending.
5. Exception #1: If a polyatomic ion, use its special name.

Practice Time!

Write the name of the ionic compounds based on the chemical formulas below.

1. RbCl2
2. (NH4)3PO4
3. Ni(OH)2

Rubidium chloride

Ammonium phosphate

Nickel (II) hydroxide

SUMMARY: Writing Chemical Formulas for Ionic Compounds

Name  Formula

1. Write down the ions with their charges.
2. Determine the number of each ion needed to follow the rule of zero charge.

(aka “criss cross applesauce”) (keep subscripts outside of parentheses and don’t change ANYTHING inside!)

1. Write the formula with subscripts.
2. Reduce/simplify (if needed).

Practice Time!

Write the chemical formulas for the ionic compounds listed below.

1. Sodium chloride
2. Aluminum chlorate
3. Iron (III) oxide

NaCl

Al(ClO3)3

Fe2O3

Helpful Hints for Ionic Compounds

• When determining the Roman numeral for a transitional metal, try to reverse crisscross first.
• If the subscript doesn’t match the charge of the known nonmetal, then it must have been simplified.
• When it doesn’t match, do a little trial and error. Double check your work by going the opposite way (determining formula from name) and see if your results match what you started with.
• Always put parentheses around polyatomic ions so you remember to “protect” them.
• You CANNOT change the subscripts of the polyatomic ions, so using parentheses will help you to remember that!