Unit 7

Naming and FormulasChapter 9-10

Ionic Compounds

Ionic compounds are electrically neutral, even though they are composed of charged ions Total positive charge equals total

negative charge

Determining Formulas

Must be electrically neutral Total positive charge must equal total

negative charge Use oxidation numbers from

Periodic Table Group 1 +1 Group 2 +2 Group 13 +3 Group 15 -3 Group 16 -2 Group 17 -1

Determining Formulas

Determine number of each ion to balance out charge Use as subscript for element symbol Ex: CaCl2, Na3PO4, Mg(NO3)2

Write Positive Ion First

Formula must be smallest whole-number ratio

Example

Sodium and Chlorine

Na+ Cl-

Na1Cl1

NaCl

Example

Calcium and Fluorine

CaF2

Ca+2 F- F-

Ca1F2

Examples

Potassium and Oxygen

K2O

K+ O-2K+

K2O1

Polyatomic Ions

Group of atoms that collectively have gained or lost electrons (Table E)

Sodium and Nitrate

Na+ (NO3)-

Na1(NO3)1

NaNO3

More Examples

Potassium and Sulfate

Ammonium and Sulfur

K2SO4

(NH4)2S

Short-cut (criss-cross method)

Magnesium and Phosphate

Mg3(PO4)2

Mg+2 PO4-3

Short-cut (criss-cross method)

Magnesium and Carbonate

Mg2(CO3)2

Mg+2 CO3-2

MgCO3

Must Simplify

Naming Ions

Positive Ions, cations, simply retain their name. Na+ Sodium Ion Mg2+ Magnesium Ion

Naming Ions

Negative Ions, anions, change ending of element to –ide Cl- Chloride Ion Br- Bromide Ion

Unique Anions Names N3- Nitride Ion

O2- Oxide Ion

S2- Sulfide Ion

P3- Phosphide Ion

Stock System

Used when the metal has more than one positive oxidation number

Use a roman numeral to indicate the charge of the ion

Roman NumeralsCation Charge

Roman Numeral

+1 I

+2 II

+3 III

+4 IV

+5 V

+6 VI

+7 VII

+8 VIII

Stock System Examples

Fe+2 Iron(II) Cu+ Copper(I) Mn+7 Manganese(VII) Au+3 Gold(III) Cr+6 Chromium(VI) Pb+4 Lead(IV)

Polyatomic Ions

Selected polyatomic ions are on Table E in the Reference Tables.

Polyatomic ions keep their names in most chemical names

Naming Systems

Ionic System Stock System (Roman Numerals)

Binary Covalent System (Prefixes)

When to use ionic system

First element is a metal NaCl

More than 2 elements, meaning polyatomic ion is involved NH4Cl

Naming Ionic Compounds

Name positive ion first, then negative ion. NaCl Sodium chloride Fe(OH)2 Iron(II) hydroxide

Binary Covalent Compounds

Use when compound is 2 nonmetals Including metalloids

Use a prefix system to indicate the number of atoms for each element

Second element ends in -ide

Prefixes

Number of atoms Prefix

1 mono-

2 di-

3 tri-

4 tetra-

5 penta-

6 hexa-

7 hepta-

8 octa-

Example

N2Cl3 Dinitrogen Trichloride

Exceptions

When there is only one atom of the first element, do not use mono- prefix. CO2

Carbon dioxide OF2

Oxygen difluoride

Exceptions

When an element starts with a vowel, drop any o or a at the end of a prefix CO

Carbon Monooxide Carbon Monoxide

P2O5

Diphosphorus Pentaoxide Diphosphorus Pentoxide