Writing Formulas

When using the criss-cross rule...

• charges become subscripts for the same ion
• subscripts become charges for the same ion
• charges become subscripts for opposite ions
• subscripts become charges for opposite ions

How do the following two elements bond together?
Na¹⁺  F^1-         

• NaF
• NaF₃
• Na₃F
• Na₁F₂

Tags

NGSS.HS-PS1-1

NGSS.HS-PS1-2

How do the following two elements bond together?
Pb⁴⁺  O^2-       

• PbO
• Pb₄O₂
• PbO₂
• Pb₂O₄

Tags

NGSS.HS-PS1-2

The chemical formula of potassium⁺¹ and iodide^-1 is

• KI
• PI
• KI₂
• K₂I

The chemical formula of Ag⁺¹ and S^-2 is

• AgS
• Ag₂S
• Au₂S
• Ag₂SO₄

Tags

NGSS.HS-PS1-1

The chemical formula of Mg⁺² and OH^-1 is

• MgOH₂
• Mg(OH)₂
• Mg(OH)
• MgH₂

Tags

NGSS.HS-PS1-1

The chemical formula of ammonium carbonate is

• NH₃CO₃
• NHCO
• NH₄CO₃
• (NH₄)₂CO₃

When adding a subscript to a polyatomic ion, you should...

• multiply any subscripts on the polyatomic ion by the subscript you are adding
• put parentheses around the polyatomic ion before adding a subscript
• write the new subscript next to any subscripts on the polyatomic ion
• put the polyatomic ion in square brackets before adding the subscript

Ionic compounds are written with

• cation first then anion
• anion first then cation
• either way is fine

When writing a formula, you find the charges

• by the column on the periodic table
• by the row of the periodic table
• by the mass number
• by the atomic number