Ionic Compounds and the Criss-Cross Method

The video tutorial explains how ionic compounds are formed by the combination of positive and negative ions, which balance each other out to form neutral compounds. It introduces the crisscross method as a quick way to determine the chemical formula of ionic compounds by using the charges of ions as subscripts. The tutorial provides practice problems to reinforce the concept and explains how to handle polyatomic ions, including when to use parentheses in chemical formulas.

What happens when positive and negative ions combine in an ionic compound?

• They repel each other.

• They form a compound with a net negative charge.

• They form a compound with a net positive charge.

• They form a neutral compound.

In the example given, what is the formula for magnesium sulfide?

• MgS2

• Mg2S

• MgS

• Mg2S3

What is the crisscross method used for?

• To determine the charges of ions.

• To balance chemical equations.

• To figure out the subscripts in ionic formulas.

• To find the molecular weight of compounds.

Using the crisscross method, what is the formula for calcium chloride?

• Ca2Cl2

• Ca2Cl

• CaCl2

• CaCl

What is the formula for potassium sulfide using the crisscross method?

• K2S2

• KS2

• K2S

• KS

When the charges of ions are the same, what is the ratio of ions in the compound?

• 1:2

• 2:2

• 2:1

• 1:1

What is the formula for sodium hydroxide?

• NaOH

• Na2OH

• NaOH2

• NaO2H

When do you need to use parentheses in ionic formulas?

• When you need more than one of a polyatomic ion.

• When the ion has a subscript.

• When the ion is a metal.

• When the ion is a non-metal.

What is the formula for calcium nitrate?

• Ca2(NO3)2

• Ca(NO3)2

• CaNO3

• Ca2(NO3)

Using the crisscross method, what is the formula for aluminum cyanide?

• Al3(CN)3

• Al3CN

• Al(CN)3

• AlCN