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