Ionic Compounds Ionic Compounds

Chemistry Joke Q: Why do chemists like nitrates so much? A: They’re cheaper than day rates!

A Review  Ion : atom or group of atoms that have a positive or negative charge  Ions form when an atom or group of atoms gains or loses electrons  METALS lose electrons to form positive CATIONS.  NONMETALS gain electrons to form negative ANIONS

Monatomic Ions  Ions consisting of only 1 atom – The charge for ions formed from representative elements can be determined by looking at the periodic table  Group 1A metals form cations with a 1+ charge  Group 2A metals form cations with a 2+ charge  Group 3A metals form cations with a 3+ charge  Group 5A nonmetals form anions with a 3- charge  Group 6A nonmetals form anions with a 2- charge  Group 7A nonmetals form anions with a 1- charge  Group 8A elements do not form ions Having One Atom!

Polyatomic Ions  Tightly bound groups of atoms that behave as a unit and carry a charge  Ex: The 10 you had to memorize.  1- charge:  2- charge:  3- charge:  1+ charge: NO 3 - NO 2 - OH - ClO 3 - C 2 H 3 O 2 - CO 3 2- SO 4 2- SO 3 2- PO 4 3- NH 4 + Having Many Atoms!

Naming Monatomic Cations  The  The name of a cation is the SAME as the name of the element!!  Ex: Na atom forms a sodium cation  Ex: Li atom forms a lithium cation  How would you name the following ion: Al +3 Al +3 Aluminum ion

Naming Monatomic Anions  The name of a MONAtomic ion ends in “ide” Ex: Chlorine atom gains 1 electron to become the CHLORIDE anion Ex: Oxygen gains 2 electrons to become an anion named OXIDE What would we name the following ion? S -2 Sulfide ion

Practice:  What do we call: –A strontium atom when it loses 2 electrons –An iodine atom when it gains 1 electron –A phosphorus atom when it gains 3 electrons? Strontium ion Iodide ion Phosphide ion

Naming Ionic Compounds  The cation comes 1 st and keeps its name.  Monatomic anions end in “ide”  Polyatomic cations and anions keep their names. Lithium Chloride Magnesium Fluoride LiCl MgF 2 NH 4 Cl Be(OH) 2 LiNO 3 MgCO 3 K 2 SO 4 Ammonium Chloride Beryllium Hydroxide Lithium Nitrate Magnesium Carbonate Potassium Sulfate

Writing the Formulas!  Cations and anions combine in a whole number ratio that produces a neutral compound.  The total positive charge of the cations will equal the total negative charge of the anions.  For example: 1 Al +3 combines with 3 F -1 (1 x + 3) cancels with (3 x - 1)

1.Write the ions with their charges The charges are known from the periodic table or memorized for polyatomic ions. 2.Cross the charge numbers (dropping the + or -) to form the subscripts. (Subscripts of 1 are not written.) 3.Simplify the subscripts to the lowest whole number ratio 3 Step Process for Writing Ionic Formulas Criss Cross Method

Writing Formulas for Ionic Compounds  Write the formula for magnesium chloride. 1.Write the ions with their charges The charges are known from the periodic table. 2.Cross the charge numbers (dropping the + or -) to form the subscripts. (Subscripts of 1 are not written.) 3.Simplify the subscripts to the lowest whole number ratio Magnesium is in Group 2A and forms a 2+ charge. Chlorine is in Group 7A and forms a 1- charge. Mg 2+ Cl 1- MgCl MgCl 2

Writing Formulas for Ionic Compounds  Write the formula for beryllium oxide. 1.Write the ions with their charges The charges are known from the periodic table. 2.Cross the charge numbers (dropping the + or -) to form the subscripts 3.Simplify the subscripts to the lowest whole number ratio. (If both subscripts are the same, they can be dropped.) Beryllium is in Group 2A and forms a 2+ charge. Oxygen is in Group 6A and forms a 2- charge. Be 2+ O 2- BeO Be 2 O 2 BeO

Writing Formulas for Ionic Compounds  Follow the same 3 steps.  Just add parentheses around the polyatomic ion before it gets a subscript With Polyatomic Ions

 Write the formula for calcium hydroxide. 1.Write the ions with their charges 2.Cross the charge numbers (dropping the + or -) to form the subscripts (dropping the + or -) to form the subscripts 3.Subscripts of 1 are not written 4.Simplify the subscripts 5.Remember to add parentheses around the polyatomic ion if a subscript has been added! Writing Formulas for Polyatomic Ionic Compounds Calcium is in Group 2A and forms a 2+ charge. Hydroxide is a polyatomic ion that has a 1- charge. Ca 2+ OH 1- CaOH CaOH 2 There are 2 Hydroxide ions not just 2 Hydrogen atoms. Ca(OH) 2

Try Some  Sodium Carbonate  Potassium Hydroxide  Magnesium Phosphate Na 2 CO 3 KOH Mg 3 (PO 4 ) 2

Chemistry Joke Q: What happened when someone told a joke to two helium atoms? A: They went, “He He!!”