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 Having One Atom! 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 Many Atoms! 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: NO3- NO2- OH- ClO3- C2H3O2- CO32- SO42- SO32- PO43- NH4+

Naming Monatomic Cations 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 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 1st and keeps its name. Monatomic anions end in “ide” Polyatomic cations and anions keep their names. LiCl K2SO4 Lithium Chloride MgF2 Potassium Sulfate Magnesium Fluoride LiNO3 MgCO3 Lithium Nitrate Be(OH)2 Magnesium Carbonate Beryllium Hydroxide NH4Cl Ammonium Chloride

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)

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

Writing Formulas for Ionic Compounds Write the formula for magnesium chloride. Write the ions with their charges The charges are known from the periodic table. Cross the charge numbers (dropping the + or -) to form the subscripts. (Subscripts of 1 are not written.) 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. Mg2+ Cl1- Mg Cl MgCl2

Writing Formulas for Ionic Compounds Write the formula for beryllium oxide. Write the ions with their charges The charges are known from the periodic table. Cross the charge numbers (dropping the + or -) to form the subscripts 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. Be2+ O2- Be O Be2O2 BeO

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

Writing Formulas for Polyatomic Ionic Compounds Write the formula for calcium hydroxide. Write the ions with their charges Cross the charge numbers (dropping the + or -) to form the subscripts Subscripts of 1 are not written Simplify the subscripts Remember to add parentheses around the polyatomic ion if a subscript has been added! Calcium is in Group 2A and forms a 2+ charge. Hydroxide is a polyatomic ion that has a 1- charge. Ca2+ OH1- Ca OH There are 2 Hydroxide ions not just 2 Hydrogen atoms. CaOH2 Ca(OH)2

Try Some Na2CO3 KOH Mg3(PO4)2 Sodium Carbonate Potassium Hydroxide Magnesium Phosphate KOH Mg3(PO4)2

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