Beaker Breaker Draw the Lewis structure of the following: nitrate ion sulfate ion ammonium ion

Beaker Breaker Is the following covalent or ionically bonded? MgBr 2 NO 3 KI F 2 O

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 +1 Cl -1 Mg +2 Cl 2 -1 (Mg +2 Cl -1 Cl -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]3s 2 3p 5 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 collection of atoms within an ionic cmpd i.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 = kJ/mol Lattice E of CaO = kJ/mol M. Pt of MgO = C M. Pt. of CaO = C

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 bonding within a crystal lattice Covalent bonding forms 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 H 2 O 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 PO 4 -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