Learning Objective

In this lesson we will learn how ions and ionic compounds are named.

Learning Outcomes

By the end of this lesson you will be able to:

  • Name positive and negative monatomic ions.
  • Give examples of metals that form more than one type of ion, and show how these ions are differentiated.
  • Look up the names and formulas of polyatomic ions on a valency table.
  • Determine the names of ionic compounds from their formulas.

Naming Ions and Ionic Compounds

1 | Names for Monatomic Ions

2 | Names for Polyatomic Ions

3 | Names for Ionic Compounds

4 | Summary

 

 naming ions and ionic compounds worksheet  year 9 chemistry pdf workbook  Year 9 Chemistry Print Workbook Australian Curriculum

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Names for Monatomic Ions

  • Monatomic ions are ions that contain one type of atom.

 

Monatomic Positive Ions

  • Monatomic positive ions have the same name as the metal atoms they are formed from.
  • For example, sodium atoms (Na) form sodium ions (Na+).
  • Positive ions formed from metals among the first 20 elements are shown below.

  • Element Name Element Symbol Ion Name Ion Charge Ion Symbol
    lithium Li lithium +1 Li+
    beryllium Be beryllium +2 Be2+
    sodium Na sodium +1 Na+
    magnesium Mg magnesium +2 Mg2+
    aluminium Al aluminium +3 Al3+
    potassium K potassium +1 K+
    calcium Ca calcium +2 Ca2+

 

Metals That Form More Than One Type of Ion

  • Many transition and post-transition metals, such as iron, copper and lead, form more than one type of ion.
  • For example, copper atoms (Cu) can form copper ions with a charge of +1 (Cu+) or +2 (Cu2+).
  • Roman numerals corresponding to the size of the positive charge are written in brackets after the metal name to distinguish the different ions.
  • For example, Cu+ ions are called copper (I) ions, and Cu2+ ions are called copper (II) ions.
  • Common metals that form more than one type of ion are shown below.

  • Element Name Element Symbol Ion Name Ion Charge Ion Symbol
    chromium Cr chromium (II) +2 Cr2+
    chromium (III) +3 Cr3+
    copper Cu copper (I) +1 Cu+
    copper (II) +2 Cu2+
    iron Fe iron (II) +2 Fe2+
    iron (III) +3 Fe3+
    lead Pb lead (II) +2 Pb2+
    lead (IV) +4 Pb4+
    tin Sn tin (II) +2 Sn2+
    tin (IV) +4 Sn4+

  • Metals that form more than one type of ion can also be looked up in a valency table.

 

Monatomic Negative Ions

  • Monatomic negative ions have the same name as the non-metal atoms they are formed from, except the last part of their name is changed to “-ide”.
  • For example, chlorine atoms (Cl) form chloride ions (Cl).
  • Negative ions formed from non-metal elements are shown below.

  • Element Name Element Symbol Ion Name Ion Charge Ion Symbol
    nitrogen N nitride –3 N3–
    oxygen O oxide –2 O2–
    fluorine F fluoride –1 F
    phosphorus P phosphide –3 P3–
    sulfur S sulfide –2 S2–
    chlorine Cl chloride –1 Cl
    selenium Se selenide –2 Se2–
    bromine Br bromide –1 Br
    iodine I iodide –1 I

 


Names for Polyatomic Ions

  • Polyatomic ions are ions that contain more than one type of atom.
  • For example, sulfate ions (SO42–) consist of one sulfur atom and four oxygen atoms, and have an overall charge of –2.
  • The names of polyatomic ions cannot be predicted from their formulas.
  • They can be looked up in a valency table, but you may wish to memorise the most commonly used ones.
  • The names of common polyatomic ions are shown below.

  • Ion Name Ion Symbol
    ammonium NH4+
    hydroxide OH
    nitrate NO3
    hydrogen carbonate HCO3
    acetate CH3COO
    sulfate SO42–
    carbonate CO32–
    phosphate PO43–

Click here for a downloadable valency table.

 


Names for Ionic Compounds

  • To form the name of an ionic compound, simply join the names of the positive and negative ions together.
  • The positive ion forms the first part of the name and the negative ion forms the second part of the name.
  • For example, potassium ions (K+) and bromide ions (Br) combine to form the ionic compound potassium bromide (KBr).
  • Examples of common ionic compounds are shown below.

  • Positive Ion Name Positive Ion Symbol Negative Ion Name Negative Ion Symbol Compound Name Compound Formula*
    magnesium Mg2+ oxide O2– magnesium oxide MgO
    aluminium Al3+ nitride N3– aluminium nitride AlN
    iron (III) Fe3+ chloride Cl iron (III) chloride FeCl3
    sodium Na+ sulfate SO42– sodium sulfate Na2SO4
    calcium Ca2+ carbonate CO32– calcium carbonate CaCO3
    lead (IV) Pb4+ fluoride F lead (IV) fluoride PbF4
    ammonium NH4+ hydroxide OH ammonium hydroxide NH4OH

  • * We will learn how the formulas for ionic compounds are determined in the next lesson.

 


Summary

  • Monatomic ions are ions that contain one type of atom.
  • Polyatomic ions are ions that contain more than one type of atom.
  • Monatomic positive ions have the same name as the metal atoms they are formed from.
  • For metals that form more than one type of ion, Roman numerals corresponding to the size of the positive charge are used to distinguish between the different ions.
  • Monatomic negative ions have the same name as the non-metal atoms they are formed from, except the last part of their name is changed to “-ide”.
  • The names of polyatomic ions cannot be predicted from their formulas, but can be looked up in a valency table.
  • The names of ionic compounds are derived by joining the names of the positive and negative ions they are composed of.
  • The positive ion forms the first part of the compound name.
  • The negative ion forms the second part of the compound name.

 
sodium chloride ions lattice

Sodium chloride lattice, showing sodium and chloride ions.

 


 

 naming ions and ionic compounds worksheet  year 9 chemistry pdf workbook  Year 9 Chemistry Print Workbook Australian Curriculum

Click images to preview the worksheet for this lesson and the Year 9 Chemistry Workbook (PDF and print versions)