Bonding Unit Learning Goal #2: Compare covalent, ionic, and metallic bonds with respect to electron behavior and relative bond strength.

The type of bond can usually be calculated by finding the difference in electronegativity of the two atoms that are going together. This table is found on page 304 of the text.

Electronegativity Difference If the difference in electronegativities is between: – 1.7 to 4.0: Ionic – 0.3 to 1.7: Polar Covalent – 0.0 to 0.3: Non-Polar Covalent Example: NaCl Na = 0.8, Cl = 3.0 Difference is 2.2, so this is an ionic bond!

Bonding spectrum 100% covalent 100% ionic A + B - A B Increasing  EN Increasing polarity Transfer

IONIC BOND bond formed between two ions by the transfer of electrons Metal + Nonmetal

Opposites Attract!

Ionic Bond Characteristics  One atom gains, one loses electrons.  Produce charged ions in all states.  Electrical attraction between ions of opposite charge.  Between atoms of metals and nonmetals with very different electronegativity  Strong Bond but not as strong as a covalent bond.

Ionic Bond Characteristics  Crystalline solid.  Very high melting point.  Soluble in H 2 O.  Insoluble in nonpolar solvents.  Nonconductor of heat and electricity in solid form.  Conducts electricity in aqueous solutions or when melted.  Examples: NaCl, CaCO 3

Ionic Bond

COVALENT BOND bond formed by the sharing of electrons Nonmetal + Nonmetal

Covalent Bond Atoms can form molecules by sharing electrons in the covalent bond. This is done only among non-metal atoms.

Covalent Bond Characteristics  Between nonmetallic elements of similar electronegativity.  Formed by sharing electron pairs  Stable non-ionizing particles  Strongest bond type

 Gas, liquid, or a soft solid at room temperature.  Low melting point and low boiling point.  Most are Insoluble in H 2 O  Soluble in nonpolar solvents.  Nonconductor of heat and electricity.  Nonlustrous Covalent Bond Characteristics

The Covalent Bond Shared electrons are attracted to the nuclei of both atoms. They move back and forth between the outer energy levels of each atom in the covalent bond. So, each atom has a stable outer energy level some of the time.

when electrons are shared equally NONPOLAR COVALENT BONDS H 2 or Cl 2

Nonpolar Covalent Molecules Equal distribution of charge around a central atom. Molecule has a symmetrical shape

when electrons are shared but shared unequally POLAR COVALENT BONDS OH -

Polar Covalent Molecules Electrons are shared, but not equally. Some atoms have a stronger pull for the electrons. Molecule not symmetrical in shape (unbalanced).

METALLIC BOND bond found in metals; holds metal atoms together very strongly Metal + Metal

Metallic Bond Characteristics Formed between atoms of metallic elements Electron cloud around atoms In metals, valence electrons are shared, free to move about. Good conductors of heat and electricity in all states. Strong bond, but weakest of the three bond types.

Metallic Bond Characteristics Malleable solid High melting point and boiling point. Insoluble in H 2 O. Insoluble in nonpolar solvents. Lustrous Examples: gold, copper

Metals Form Alloys Metals do not combine with metals. They form Alloys which is a solution of a metal in a metal. Examples are steel, brass, bronze and pewter.

Bond Type Review

Na Cl NaCl + - electron transfer and the formation of ions This is the formation ionic bond of an ionic bond.

This is the formation covalent bond of a covalent bond. Cl 2 Cl sharing of a pair of electrons and the formation of molecules

Metallic Bonds Fe Positive Nuclei Electrons Freely Moving Metal atoms tightly packed with electrons moving freely around the positive nuclei.

Covalent BondsIonic BondsMetallic Bonds ShapeDefinite ShapeNo Definite Shape Definite Shape Boiling PointLowHigh ExamplesMethane (CH 4 )Sodium Chloride (NaCl) Iron Metal Occurs Between2 Non-MetalsMetal and Non- metal 2 Metals FormationSharing of Electrons Transfer of Electrons The valence electrons are detached from the atoms but not held by any of the other atoms. PolarityLowHigh Melting PointLowHigh Electronegativity Difference LowHighLow State at Room Temperature Liquid Or Gaseous Solid

1.Explain how gaining, losing or sharing valence electrons will help predict the type of bond between two elements? 2.How does a bond type describe what behavior the valence electrons are exhibiting? 3.Which are the strongest and weakest types of bonds? Essential Questions