Lecture 6 9/12/05

Seminar today at 4 pm

Compounds & MoleculesCompounds & Molecules

COMPOUNDS - combination of 2 or more elements in definite ratios

Has unique characteristics from element

H2O

MOLECULES are the smallest unit of a compound that retains the characteristics of the compound.

Ionic Compounds vs. Molecular Compounds

CATIONS – Positive ion

Li → 1 e- + Li+

ANION – Negative ion

F + 1 e- → F-

Predicting Charges on Monatomic IonsPredicting Charges on Monatomic Ions

Naming cations

For metals: (name + ion) Al3+ - Aluminum ion

For metals with multiple possible charges: Use Roman numeral in parenthesis for charge -ous (lower charge) vs. –ic (higher charge) Copper (II) = cupric ion Copper (I) ion = cuprous ion

NH4+ is ammonium ion

Naming anions

Monatomic ion: (-ide)Carbide (C4-)Nitride (N3-)Phosphide (P3-)Oxide (O2-)Fluoride (F-)Halides

Naming Polyatomic anionsOxoanions Per . . . ate . . . ate . . . itehypo. . . ite

Incr

easi

ng O

con

tent

NO3- and NO2

-

ClO4- and ClO3

- and ClO2- and

ClO-

Ionic CompoundsComposed of ions but neutral

Na+ and Cl-

Ca2+ and CO32-

Ca2+ and Cl-

Ti4+ and O2-

Electrostatic Forces - Coulomb’s Law

Force of attraction = (charge on +)(charge on -)

(distance between ions)2

Electrostatic Forces - Coulomb’s Law

Force of attraction = (charge on +)(charge on -)

(distance between ions)2

As ion charge increases, the attractive force _____.

As the distance between ions increases, the attractive force ____.

Importance of Coulomb’s Law

NaClNa+ and Cl-,m.p. 804 oC

MgOMg2+ and O2-

m.p. 2800 oC

Is a compound ionic?

1. Most metal-containing compounds are ionic.

2. Likely non-ionic if no metals

3. Look for polyatomic molecules like NH4+

1. Ammonium ion IS NOT an ionic compound, but can be used to form an ionic compound