Warm Up

• What is the charge of a cation? negative or positive

• How are cations formed?

• What is the charge of an anion? negative or positive

• How are anions formed?

State the number of electrons gained or lost in forming the following ions:

Mg2+

Rb1+

Br-

Al3+

State the number of electrons gained or lost in forming the following ions:

Mg2+ Lost 2 electronsRb1+ Lost 1 electronsBr- Gained 1 electronAl3+ Lost 3 electrons

Write the formula unit (element symbol and charge) for the following ions:

• Sodium ion• Bromide• Sulfide• Barium ion

Write the formula unit (element symbol and charge) for the following ions:

• Sodium ion Na+

• Bromide Br-

• Sulfide S2-

• Barium ion Ba2+

6.4Writing Chemical FormulasWriting Chemical Formulas

Binary Ionic compounds (2 elements)

Chemical Formula Rule: 1. Identify ion symbols and charges2.Write cation symbol 1st followed by the anion

symbol3. Balance charge (“cross multiplication”)Example: Write the formula for sodium chloride.

Na+ and Cl-

NaCl

Na+ O2-

Formula: Na2O

Na+ Na+ O2-

*** You do not need to write a 1, if the subscript is not present you assume it is one!!

Trick for balancing

“cross multiply”Ca2+ Cl-

Ca Cl2

Ca2+ Cl- Cl-

Naming the ionic compound when given a formula

1. Cation full name followed by the anion(-ide ending)

Naming: Cation + anion-ide

Example: • CaCl2 Calcium chloride

• NaCl Sodium Chloride

When looking at the name, is the number of atoms indicated?

How are you supposed to figure out the number of atoms???

You try it!

Li+ S2-

Write the formula and name!

You try it!

Li+ S2-

Write the formula and name!

Li2S

Lithium Sulfide

The ions of calcium and sulfur form a binary ionic compound.

Write the formula and name of this resulting compound:

Calcium ion and Sulfide

Write the formula and name of this resulting compound:

CaSCalcium sulfide

You try it!

Write the ions, chemical formula and chemical name of the ionic compound formed when potassium and oxygen ions interact.

Ions: Chemical Formula:Chemical name:

Write the ions, chemical formula and chemical name of the ionic compound formed when potassium and oxygen ions interact.

Ions: K+ O2-

Chemical Formula: K2O

Chemical Name: Potassium oxide

Ternary Compounds

one ion is monatomic other is a polyatomic ion…….

Example: Lead NitratePb2+ and ( NO3

- )

Formula: Pb (NO3)2

You try it!

Sodium hydrogen phosphateNa1+ HPO4

2-

Write the formula:

Sodium hydrogen phosphateNa1+ HPO4

2-

Write the formula:Na2HPO4

6.3 and 6.4In Class Practice