Mastering Ionic Compound Formulas with the Crisscross Method

The video tutorial explains how ionic compounds are formed by balancing positive and negative ions to achieve a neutral charge. 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 several practice problems to illustrate the method, including examples with polyatomic ions, where parentheses are used when more than one polyatomic ion is needed. The video aims to help viewers understand and apply the crisscross method effectively in writing ionic formulas.

What is the result when a magnesium ion with a +2 charge combines with a sulfide ion with a -2 charge?

• Mg2S2

• MgS2

• Mg2S

• MgS

How many chloride ions are needed to balance a calcium ion with a +2 charge?

• One

• Two

• Three

• Four

What is the formula for a compound formed by potassium ions (K+) and sulfide ions (S2-)?

• KS

• K2S

• KS2

• K2S2

When using the crisscross method, what is the formula for a compound formed by iron (Fe3+) and oxygen (O2-)?

• Fe3O2

• Fe2O3

• FeO

• FeO2

What is the correct formula for sodium chloride using the crisscross method?

• Na2Cl2

• NaCl2

• Na2Cl

• NaCl

How do you write the formula for calcium nitrate using the crisscross method?

• CaNO3

• Ca(NO3)2

• Ca2NO3

• Ca2(NO3)2

What is the formula for lithium phosphate using the crisscross method?

• Li3(PO4)2

• Li(PO4)3

• Li3PO4

• LiPO4

When writing the formula for aluminum cyanide, why are parentheses used around the cyanide ion?

• To indicate a single ion

• To show multiple ions are needed

• To separate it from other ions

• To denote a complex ion

What is the formula for iron(III) carbonate using the crisscross method?

• Fe(CO3)2

• FeCO3

• Fe2(CO3)3

• Fe3(CO3)2

What is the main purpose of the crisscross method in writing ionic formulas?

• To balance chemical equations

• To determine the subscripts in ionic compounds

• To predict the color of compounds

• To identify the charge of ions