Beaker BreakerDraw the Lewis structure of

the following:• nitrate ion

• sulfate ion

• ammonium ion

Beaker Breaker

• Is the following covalent or ionically bonded?

• MgBr2

• NO3

• KI

• F2O

6-3

Ionic Bonding

Ionic Compound

• composed of positive and negative ions that are combined so that the number of positive charges are equal to (cancel out) the number of negative charges

• Na+1Cl-1

• Mg+2Cl2-1 (Mg+2Cl-1Cl-1)

• Not called “molecules”…but called “formula units”

From a potential energy standpoint, why do ions form orderly arrangements known

as crystal lattices?

Formation of Ionic Cmpds

• Atoms form ions when they lose or gain e-s and attain a noble-gas configuration

• Ions reach a lower potential E through the electrical forces of attraction between oppositely charged particles when they combine in an orderly arrangement known as a crystal lattice.

• Forces of repulsion (like-charged ions, adjacent e- clouds) balance the forces of attraction (opp-charged ions, nuclei-electron of adjacent ions)

•Na: [Ne]3s 1

•Cl: [Ne]3s23p5

•Na+1 sodium ion Cl-1 chloride ion [Ne] [Ar]

Sodium chloride, NaCl

• The chemical formula of an ionic cmpd is the simplest formula of the cmpd…it does NOT represent a discrete GROUP of separate atoms like a molecule does

• Covalent bonding: simplest unit is a molecule

• Ionic bonding: simples unit is a formula unit

“Molecules” – discrete gps of atoms covalently bonded

“Formula units” –simplest collectionof atoms within anionic cmpdi.e. NaCl..Na+1 doesn’t“belong” to any one neighbor

Lattice Energy• Term used to describe bond strength in

ionic cmpds• Energy released when one mole of an ionic

crystalline cmpd is formed from gaseous ions

• Negative value indicates that E is released • The larger the value, the more E released,

the more stable the bonding will be (true also for bond E)

• i.e. NaCl –787.5 kJ/mol

Which ionic cmpd has a higher melting point….MgO or CaO ?

• Lattice E must be overcome in order for an ionic cmpd to melt

• Lattice E of MgO = -3760 kJ/mol

• Lattice E of CaO = - 3383 kJ/mol

• M. Pt of MgO = 2852 0C

• M. Pt. of CaO = 275 0C

How do the forces that holds ions together compare to the forces that hold

molecules together?

• How do the forces BETWEEN ions compare to the forces BETWEEN molecules?

• What effect will these differences have on properties like boiling/melting points, hardness, brittleness?

•Ionic bondingwithin a crystal lattice

•Covalent bondingforms a “molecule”

Ionic vs. Covalent Properties

IONIC

• strong force that holds ions together (+, --)

• stronger forces of attraction between ions

• ∴higher melting & boiling pts; don’t vaporize at room temp

MOLECULAR

• strong covalent bond within the atoms of each molecule

• weaker F of attraction between molecules

• ∴melt at low temps & many vaporize at room temp

Other ionic properties…

• Hardness: tough for one layer to slide past another hard∴

• Brittle: if ionic layers DO shift, they “snap”

How does conductivity in ionic cmpds compare to that in

molecular cmpds?

Ionic vs. Covalent Properties

IONIC• non-conductors in

solid state because ions can’t move

• conductors in molten state

• conductors when dissolved in H2O

MOLECULAR• non-conductors in all

states

Polyatomic Ions

• A charged group of covalently bonded atoms

• Combine with ions of opposite charge to form ionic cmpds

Draw the Lewis structure for the phosphate ion

• PO4-3

• P = 5 valence e-s = 5 e-s

• 4 x O = 4 x 6 valence e-s = 24 e-s

• -3 charge = 3 additional e-s + = 3 e-s

32 e-s