3.1 Bonding

Ionic Bonding • • • • • Cl Na • • • • • [ Na ]+ [ Cl ]- • • • • • • Form between a metal and a nonmetal Simplest expressed form is called formula unit Valence electrons are “stolen” Typical ionic bonds are alkali halides such as sodium chloride (NaCl) • • • • • Cl Metals lose electrons to get a stable outer shell Nonmetals gain electrons to get a stable outer shell Na • • • • • [ Na ]+ [ Cl ]- • • • • • • Positive ions are called cations Negative ions are called anions

Ionic Properties Very high melting points. Brittle crystals. Many dissolve in water. Good conductors of electricity if melted or dissolved. Acids Ionic compounds that have H+ and an anion Molecular formula always starts with H Name is derived from its anion and always ends with the word, acid.

Covalent Bonding Electrons are shared by both nuclei Molecules are the smallest units of covalent compounds Diatomic- element that always occurs in pairs Br2, I2, N2, Cl2, H2, O2, F2 Know these H2O Water NH3 Ammonia CH4 Methane

Covalent Properties Low melting points. Many are liquids and gases at room temperature. Polar covalent molecules dissolve in water. Nonconductors of electricity.

Lewis Dot Diagrams NH3 H • • H N • • • • H • • H H N H • • Dot Diagram Steps 1. Draw out atoms with valence electrons 2. Connect 2 e- to share until all atoms have full shells 3. Redraw H • • H N • • • • H • • Sometimes more than one pair of electrons are shared: Double Bonds= 2 pairs of electrons Triple Bonds= 3 pairs of electrons H Final Answer H N H • •

Drawing Hints Put the single atom in the middle of the dot diagram Hydrogen is never in the middle of the dot diagram When redrawing, we use dashes to represent 2 shared electrons Remember to redraw the nonbonding electrons

Sample Problems Draw CH4 PCl3 SH2 HCl CO2 BH3

CH4

PCl3

SH2

HCl

CO2

BH3 *note: B violates the octet rule (w/ 6e-) *other exceptions, Be needs 4 valence e-, nonmetals in period 3 or higher MAY have 10 or 12 valence e-