Standard 3.1
Ionic Compounds

Formation of ionic compounds
• Ionic compounds form when oppositely charged cations and anions are attracted to one another.

Formation of ionic compounds
• Ionic compounds form when oppositely charged cations and anions are attracted to one another.
• Example: Sodium loses an electron to form the cation Na + . Chlorine gains an electron to form the anion Cl .

Formation of ionic compounds
• Ionic compounds form when oppositely charged cations and anions are attracted to one another.
• Example: Sodium loses an electron to form the cation Na + . Chlorine gains an electron to form the anion Cl .
• The opposite charges cause the two ions to stick together forming the compound NaCl.

Formation of ionic compounds
• Because metals form cations and nonmetals form anions, ionic compounds contain both metals and nonmetals.

•
Binary ionic compounds
•
• Binary means 2, so a binary compound consists of just 2 elements; a metal and a nonmetal.

Everybody on the left side of the room will be an atom of lithium. Everybody on the right side of the room will be fluorine. Please hold your element’s valence electrons in your hand.

Everybody on the left side of the room will be an atom of lithium. Everybody on the right side of the room will be fluorine. Please hold your element’s valence electrons in your hand.
• Walk around the room and exchange electrons with your classmates in such a way that both you and your classmates end up being stable.
Stay with your trading partner(s) when everyone in your trading group has become stable.

Everybody on the left side of the room will be an atom of lithium. Everybody on the right side of the room will be fluorine. Please hold your element’s valence electrons in your hand.
• Walk around the room and exchange electrons with your classmates in such a way that both you and your classmates end up being stable.
Stay with your trading partner(s) when everyone in your trading group has become stable.
• You should be in pairs of one lithium and one fluorine (LiF)

This time, the people on the left side will be atoms of sulfur while the people on the right side will be atoms of potassium.

This time, the people on the left side will be atoms of sulfur while the people on the right side will be atoms of potassium.
• Walk around the room and exchange electrons with your classmates in such a way that both you and your classmates end up being stable.
Stay with your trading partner(s) when everyone in your trading group has become stable.

This time, the people on the left side will be atoms of sulfur while the people on the right side will be atoms of potassium.
• Walk around the room and exchange electrons with your classmates in such a way that both you and your classmates end up being stable.
Stay with your trading partner(s) when everyone in your trading group has become stable.
• You should have 2 potassium atoms for each sulfur this time (K
2
S)

This time, the people on the left side will be atoms of aluminum while the people on the right side will be atoms of oxygen.

This time, the people on the left side will be atoms of aluminum while the people on the right side will be atoms of oxygen.
• Walk around the room and exchange electrons with your classmates in such a way that both you and your classmates end up being stable.
Stay with your trading partner(s) when everyone in your trading group has become stable.

This time, the people on the left side will be atoms of aluminum while the people on the right side will be atoms of oxygen.
• Walk around the room and exchange electrons with your classmates in such a way that both you and your classmates end up being stable.
Stay with your trading partner(s) when everyone in your trading group has become stable.
• Successful groups should have 2 aluminum atoms and 3 oxygen atoms (Al
2
O
3
)

Binary ionic compounds
•
• Binary means 2, so a binary compound consists of just 2 elements; a metal and a nonmetal.
• To determine the chemical formula for ionic compounds, determine the charge on each ion and criss-cross them to generate subscripts.

lithium and fluorine

lithium and fluorine
• lithium, 1 valence electron, charge of 1+

lithium and fluorine
• lithium, 1 valence electron, charge of 1+
• fluorine, 7 valence electrons, charge of 1-

lithium and fluorine
• lithium, 1 valence electron, charge of 1+
• fluorine, 7 valence electrons, charge of 1-
• Li 1+ F 1-

lithium and fluorine
• lithium, 1 valence electron, charge of 1+
• fluorine, 7 valence electrons, charge of 1-
• Li 1+ F 1-
• LiF (subscripts of one are not written)

lithium and fluorine
• lithium, 1 valence electron, charge of 1+
• fluorine, 7 valence electrons, charge of 1-
• Li 1+ F 1-
• LiF (subscripts of one are not written)
• The cation is always listed first in a chemical formula.

lithium and fluorine
• lithium, 1 valence electron, charge of 1+
• fluorine, 7 valence electrons, charge of 1-
• Li 1+ F 1-
• LiF (subscripts of one are not written)
• The cation is always listed first in a chemical formula.
• The chemical formula for a compound will never contain charges or Roman numerals.

potassium and sulfur

potassium and sulfur
• potassium, 1 valence electron, charge of 1+

potassium and sulfur
• potassium, 1 valence electron, charge of 1+
• sulfur, 6 valence electrons, charge of 2-

potassium and sulfur
• potassium, 1 valence electron, charge of 1+
• sulfur, 6 valence electrons, charge of 2-
• K 1+ S 2-

potassium and sulfur
• potassium, 1 valence electron, charge of 1+
• sulfur, 6 valence electrons, charge of 2-
• K 1+ S 2-
• K
2
S (The subscript of 1 is never written)

aluminum and oxygen

aluminum and oxygen
• aluminum, 3 valence electrons, charge of 3+

aluminum and oxygen
• aluminum, 3 valence electrons, charge of 3+
• oxygen, 6 valence electrons, charge of 2-

aluminum and oxygen
• aluminum, 3 valence electrons, charge of 3+
• oxygen, 6 valence electrons, charge of 2-
• Al 3+ O 2-

aluminum and oxygen
• aluminum, 3 valence electrons, charge of 3+
• oxygen, 6 valence electrons, charge of 2-
• Al 3+ O 2-
• Al
2
O
3

What compound will form when calcium combines with bromine?

What compound will form when calcium combines with bromine?
CaBr
2

What compound will form when iron(II) combines with sulfur?

What compound will form when iron(II) combines with sulfur?
Fe
2
S
2 which simplifies to
FeS

Binary ionic compounds
• Binary means 2, so a binary compound consists of just 2 elements; a metal and a nonmetal.
• To determine the chemical formula for ionic compounds, determine the charge on each ion and criss-cross them to generate subscripts.
• Simplify the subscripts if they are divisible by the same number.

Polyatomic ions
• A group of atoms that collectively form a single ion.

Polyatomic ions
• A group of atoms that collectively form a single ion.
• A sulfate ion is formed when one sulfur atom combines with 4 oxygen atoms to form an ion with a charge of 2- (SO
4
2).

Polyatomic ions
• A group of atoms that collectively form a single ion.
• A sulfate ion is formed when one sulfur atom combines with 4 oxygen atoms to form an ion with a charge of 2- (SO
4
2).
• The subscripts in polyatomic ions should never be changed.

Write the formula for the compound that will form when aluminum ions combine with sulfate ions.

Write the formula for the compound that will form when aluminum ions combine with sulfate ions.
• Al 3+ SO
4
2-

Write the formula for the compound that will form when aluminum ions combine with sulfate ions.
• Al 3+ SO
4
2-
• Al
2
(SO
4
)
3

Write the formula for the compound that will form when aluminum ions combine with sulfate ions.
• Al 3+ SO
4
2-
• Al
2
(SO
4
)
3
• The subscripts of the polyatomic ion cannot be changed. The number of sulfate ions needed goes outside the parentheses.
Parentheses are not needed if the subscript on the polyatomic ion is 1.