3.2 Ionic and Covalent Bonding SCH3U Ms. Munir

Isoelectronic Cl- is isoelectronic with Ar [18 e- each] When 2 or more atoms or ions have the same electron configuration, they are said to be isoelectronic with each other. Cl- is isoelectronic with Ar [18 e- each]

Ionic Bonding Consider NaCl: Na has a very low EN, Cl has a very high EN. Na transfers its valence electron to Cl. Sodium becomes Na+ and chlorine becomes Cl−.

Transferring Multiple Electrons The EN difference for MgO is 3.4 − 1.3 = 2.1. MgO is an ionic compound.

Ionic Bonding That Involves More Than Two Ions

Explaining the Conductivity of Ionic Compounds Ionic compounds do not conduct electricity in their solid state. They are very good conductors in their liquid state. Electrical current can flow only if charged particles are available to move and carry the current.

Covalent Bonding If two atoms of the same element form a bond, they share their electrons equally in a pure covalent bond. Elements that bond to each other in this way are known as diatomic elements.

Multiple Covalent Bonds In covalent bonding, atoms sometimes share 2 or 3 pairs of electrons. In the diatomic oxygen, they share 2 pairs of electrons. This is called a double bond.

Triple bond When atoms share three pairs of electrons, they form a triple bond. E.g., Diatomic nitrogen.

Explaining the Low Conductivity of Covalent Compounds Covalent compounds do not break up into ions when they melt or boil. Their atoms remain bonded together as molecules. For this reason, covalent compounds are also called molecular compounds. The molecules that make up a pure covalent compound cannot carry a current, even if the compound is in its liquid state or in solution.

Evidence for Intermolecular Forces The forces that bond the atoms to each other within a molecule are called intramolecular forces. The forces that bond molecules to each other are called intermolecular forces.

Continued… Because pure covalent compounds have low melting and boiling points, you know that the intermolecular forces must be very weak compared with the intramolecular forces.

Metallic Bonding In metallic bonding, atoms release their electrons to a shared pool of electrons. Think of a metal as a non-rigid arrangement of metal ions in a sea of free electrons. The force that holds metal atoms together is called a metallic bond. Metallic bonding does not have a particular orientation in space. When a hammer pounds metal, the atoms can slide past one another allowing metals to be easily hammered into sheets.

Practice P 84 # 1 – 6 McGraw hill P 73 # 1 – 8 Nelson