Writing Formulae and Naming Chapter 19 Section 3a

Binary Ionic Compounds Charge can also be represented by oxidation number Charge can also be represented by oxidation number Oxidation number represents the movement of electrons no matter what kind of bonding Oxidation number represents the movement of electrons no matter what kind of bonding Oxidation number of ion is the same as its charge Oxidation number of ion is the same as its charge Formula must be written so that sum of charges for all ions is zero Formula must be written so that sum of charges for all ions is zero

Rules for Writing Formulae Write the symbol for the positive ion or polyatomic ion first Write the symbol for the positive ion or polyatomic ion first Write the symbol for the negative ion or polyatomic ion next Write the symbol for the negative ion or polyatomic ion next Use subscripts to multiply the ions so that sum of charges is zero Use subscripts to multiply the ions so that sum of charges is zero

Special Ions Transition elements can have more than one charge Transition elements can have more than one charge They will always be positive They will always be positive To indicate charge, Roman numeral is used To indicate charge, Roman numeral is used Examples: Examples: Copper (I) Cu +1 Copper (I) Cu +1 Copper (II)Cu +2 Copper (II)Cu +2 Iron (III)Fe +3 Iron (III)Fe +3

Examples Write the formula for sodium chloride Write the formula for sodium chloride Write the formula for magnesium fluoride Write the formula for magnesium fluoride Write the formula for lead (IV) phosphide Write the formula for lead (IV) phosphide Write the formula for copper (I) oxide Write the formula for copper (I) oxide Write the formula for copper (II) oxide Write the formula for copper (II) oxide

Some Special Ions Polyatomic ions: Polyatomic ions: A group of atoms bonded covalently that have gained or lost electrons and become ions A group of atoms bonded covalently that have gained or lost electrons and become ions Examples: Examples: AmmoniumNH 4 + AmmoniumNH 4 + AcetateC 2 H 3 O 2 - AcetateC 2 H 3 O 2 - HydroxideOH- HydroxideOH- CarbonateCO 3 -2 CarbonateCO 3 -2 SulfateSO 4 -2 SulfateSO 4 -2 PhosphatePO 4 -3 PhosphatePO 4 -3

Naming Compounds Rules: Rules: Write the name of the positive ion Write the name of the positive ion If the positive ion is a transition element, use a Roman numeral to indicate its charge If the positive ion is a transition element, use a Roman numeral to indicate its charge Write the root name of the negative ion Write the root name of the negative ion Add the suffix –ide to the negative name Add the suffix –ide to the negative name

Naming Example Name the compounds: Name the compounds: KI KI MgOH MgOH Al 2 O 3 Al 2 O 3 PCl 3 PCl 3