Writing Ionic CompoundsWriting Ionic CompoundsThe “Swap & Drop” MethodThe “Swap & Drop” Method

Swap & Drop MethodSwap & Drop Method

Potassium Ion

KChlorine Ion

Cl+ -1 1

Step 1: Drop the signs.

For Ionic Compounds Only!

Swap & Drop MethodSwap & Drop Method

Potassium Ion

KChlorine Ion

Cl1 1

Step 2: Swap Values.

Swap & Drop MethodSwap & Drop Method

Potassium Ion

KChlorine Ion

Cl1 1

Step 3: Drop Values to Subscripts.

1 1

Swap & Drop MethodSwap & Drop MethodPotassium Ion

KChlorine Ion

ClStep 4: When the values are the same, then they can be erased. The number (1) is never required.

Potassium Chloride

This 4This 4thth rule applies to all situations. rule applies to all situations.

Example: CuExample: Cu2+2+ and CO and CO332-2-

Both have 2’s, which can be erased to Both have 2’s, which can be erased to formform

CuCOCuCO33

Again, when the values are the Again, when the values are the same, then they can be erased. same, then they can be erased. The number is never required.The number is never required.

Swap & Drop MethodSwap & Drop Method

Aluminum Ion

AlOxygen Ion

O+ -3 2

Step 1: Drop the signs.

Swap & Drop MethodSwap & Drop Method

Step 2: Swap Values.

Aluminum Ion

AlOxygen Ion

O3 2

Swap & Drop MethodSwap & Drop Method

Step 3: Drop values to subscripts.

Aluminum Ion

AlOxygen Ion

O 322 3

Swap & Drop MethodSwap & Drop Method

Step 4: Combine into compound.

Aluminum Ion

AlOxygen Ion

O2 3Aluminum Oxide

Swap & Drop Method:Swap & Drop Method:PolyatomicsPolyatomics

Iron (II) Ion

FePhosphate Ion

PO4+ -2 3

Step 1: Drop the signs.

Swap & Drop MethodSwap & Drop Method

Step 2: Swap Values.

Iron (II) Ion

FePhosphate Ion

PO42 3

Swap & Drop MethodSwap & Drop Method

Step 3: Drop values to subscripts.*Protect the poly with parentheses.

Iron (II) Ion

FePhosphate Ion

(PO4)23

3 2

Swap & Drop MethodSwap & Drop Method

Step 4: Combine into compound.

Iron (II) Ion

FePhosphate Ion

(PO4)3 2Iron (II) phosphate