Ionic Compounds

Forming Chemical Bonds

• Objectives– Define chemical bond– Relate chemical bond formation to

electron configuration– Describe the formation of positive and

negative ions

Chemical Bonds

• The force that holds two atoms together…– WHY?

Electron Dot structure

• Recall them…– Do some on board

• Recall “ion”

• Write electron configurations for potassium and argon– What’s the difference?– Why is argon so stable?– How could potassium achieve stability?

Ions

• How do atoms become ions?

• Positive ions– They always want to achieve the most

stable state…8 valence electrons– Look at Ne and Na’s configurations– Ionization energy is key…

Negative Ions

• Look at argon and chlorine– Anions gain electrons in bonding to

achieve noble gas configuration

Homework

• 8.1 assessment

• P.236 # 47-50; 60-66

Formation of Ionic Bond

• Objectives– Describe the formation of ionic bonds– Account for many of the physical

properties of an ionic compound– Discuss the energy involved in the

formation of an ionic bond

Ionic Bonding

• Atoms transfer electrons from one to another forming a bond between two ions.

• The electrostatic force that holds oppositely charged particles together in an ionic compound is referred to as an ionic bond

• Ionic bonds are extremely strong bonds

Ionic Bonds

• Binary compounds– Contains two different elements– Ex: MgO

• Is CaSO4 a binary compound?

• Polyatomic ion: an ion that contains more than one element– SO4-

– OH-

Properties of Ionic Compounds

• Ions packed into regular repeating patterns called crystals (crystal lattice)

Crystals

• High-energy bonds

• Melting point, boiling point and hardness all depend on strength of bond– Stronger = higher boiling and melting pts.

Properties

• High melting and boiling points - Ionic bonds are very strong - a lot of energy is needed to break them. ...

• Conductive when aqueous - Ions are charged particles, but ionic compounds can only conduct electricity if their ions are free to move.

Sodium Chloride

Potassium Chloride

Electrical Conductivity

Electrolyte

• An ionic compound whose aqueous solution conducts an electric current– NaCl, MgCl2, KF

Energy and Ionic Bond

• Lattice energy:– The energy required to separate one

mole of the ions of an ionic compound– Higher energy bonds = higher lattice

energy

Homework

• 8.2 assessment

• P.236 #51-53; 67-73