Question

write the formula / formula unit for the following compounds
determining the formula for magnesium fluoride?

1. identify the charges = mg²⁺ f¹
2. cross the charges, mg²⁺ f¹ = mg₁f₂
3. if the subscript is a 1 it does not need to be written.
4. if there is a common subscript such as 2 as in mg₂o₂, reduce it to mg₁o₁ which is also mgo.

write formula unit for the below ionic compounds

	name	cation (+)	anion (-)	formula
1	sodium chloride	na¹⁺	cl¹⁻	na¹⁺cl¹⁻ = nacl
2	aluminum chloride	al³⁺	cl¹⁻
3	aluminum phosphide
4	magnesium oxide
5	cesium fluoride
6	strontium nitride
7	lithium sulfide
8	calcium chloride
9	sodium bromide
10	beryllium iodide
11	strontium fluoride
12	aluminum fluoride
13	potassium nitride
14	sodium sulfide
15	lithium oxide
16	calcium oxide

Explanation:

Step1: Cross charges for AlCl₃

$\text{Al}^{3+} \text{Cl}^{1-}
ightarrow \text{Al}_1\text{Cl}_3 = \text{AlCl}_3$

Step2: Correct Sr charge, cross for Sr₃N₂

$\text{Sr}^{2+} \text{N}^{3-}
ightarrow \text{Sr}_3\text{N}_2$

Step3: Cross charges for Li₂S

$\text{Li}^{1+} \text{S}^{2-}
ightarrow \text{Li}_2\text{S}_1 = \text{Li}_2\text{S}$

Step4: Cross charges for CaCl₂

$\text{Ca}^{2+} \text{Cl}^{1-}
ightarrow \text{Ca}_1\text{Cl}_2 = \text{CaCl}_2$

Step5: Identify anion, cross for NaBr

$\text{Na}^{1+} \text{Br}^{1-}
ightarrow \text{NaBr}$

Step6: Correct cation, cross for BeI₂

$\text{Be}^{2+} \text{I}^{1-}
ightarrow \text{Be}_1\text{I}_2 = \text{BeI}_2$

Step7: Identify ions, cross for SrF₂

$\text{Sr}^{2+} \text{F}^{1-}
ightarrow \text{Sr}_1\text{F}_2 = \text{SrF}_2$

Step8: Identify ions, cross for AlF₃

$\text{Al}^{3+} \text{F}^{1-}
ightarrow \text{Al}_1\text{F}_3 = \text{AlF}_3$

Step9: Identify ions, cross for K₃N

$\text{K}^{1+} \text{N}^{3-}
ightarrow \text{K}_3\text{N}_1 = \text{K}_3\text{N}$

Step10: Identify ions, cross for Na₂S

$\text{Na}^{1+} \text{S}^{2-}
ightarrow \text{Na}_2\text{S}_1 = \text{Na}_2\text{S}$

Step11: Identify ions, cross for Li₂O

$\text{Li}^{1+} \text{O}^{2-}
ightarrow \text{Li}_2\text{O}_1 = \text{Li}_2\text{O}$

Step12: Identify ions, cross for CaO

$\text{Ca}^{2+} \text{O}^{2-}
ightarrow \text{Ca}_1\text{O}_1 = \text{CaO}$

Step13: Correct existing errors

1. Magnesium Oxide: $\text{Mg}^{2+} \text{O}^{2-}

ightarrow \text{MgO}$ (charge written incorrectly as $\text{Mg}^{-2}$, fixed to $\text{Mg}^{2+}$)

1. Cesium Fluoride: Anion is $\text{F}^{1-}$ (written incorrectly as $7^{-1}$, fixed), formula $\text{CsF}$

Answer:

#	Name	Cation (+)	Anion (-)	Formula
2	Aluminum Chloride	$\text{Al}^{3+}$	$\text{Cl}^{1-}$	$\text{AlCl}_3$
3	Aluminum Phosphide	$\text{Al}^{3+}$	$\text{P}^{3-}$	$\text{AlP}$
4	Magnesium Oxide	$\text{Mg}^{2+}$	$\text{O}^{2-}$	$\text{MgO}$
5	Cesium Fluoride	$\text{Cs}^{1+}$	$\text{F}^{1-}$	$\text{CsF}$
6	Strontium Nitride	$\text{Sr}^{2+}$	$\text{N}^{3-}$	$\text{Sr}_3\text{N}_2$
7	Lithium Sulfide	$\text{Li}^{1+}$	$\text{S}^{2-}$	$\text{Li}_2\text{S}$
8	Calcium Chloride	$\text{Ca}^{2+}$	$\text{Cl}^{1-}$	$\text{CaCl}_2$
9	Sodium Bromide	$\text{Na}^{1+}$	$\text{Br}^{1-}$	$\text{NaBr}$
10	Beryllium Iodide	$\text{Be}^{2+}$	$\text{I}^{1-}$	$\text{BeI}_2$
11	Strontium Fluoride	$\text{Sr}^{2+}$	$\text{F}^{1-}$	$\text{SrF}_2$
12	Aluminum Fluoride	$\text{Al}^{3+}$	$\text{F}^{1-}$	$\text{AlF}_3$
13	Potassium Nitride	$\text{K}^{1+}$	$\text{N}^{3-}$	$\text{K}_3\text{N}$
14	Sodium Sulfide	$\text{Na}^{1+}$	$\text{S}^{2-}$	$\text{Na}_2\text{S}$
15	Lithium Oxide	$\text{Li}^{1+}$	$\text{O}^{2-}$	$\text{Li}_2\text{O}$
16	Calcium Oxide	$\text{Ca}^{2+}$	$\text{O}^{2-}$	$\text{CaO}$