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 362 of your 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!

Electronegativity Chlorides of Period 2 compound LiClBeCl 2 BCl 3 CCl 4 NCl 3 OCl 2 Cl 2  EN Chlorides of Period 3 Compound NaClMgCl 2 AlCl 3 SiCl 4 PCl 3 SCl 6 Cl 2  EN large differencesmall difference The electronegativity difference -  EN = EN higher – EN lower

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

Chlorides of Period 2 compound LiClBeCl 2 BCl 3 CCl 4 NCl 3 OCl 2 Cl 2 melting point Chlorides of Period 3 compound NaClMgCl 2 AlCl 3 SiCl 4 PCl 3 SCl 6 Cl 2 melting point Can we explain the melting point behavior across a period?. What is the trend? lowhigh Conductivity - highConductivity - low CRC Handbook of Chemistry and Physics, 1995

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

Opposites Attract!

Ionic Bonds Electrons are transferred. One atom gains, one loses electrons. Electrical attraction between ions of opposite charge. Between metal – nonmetal. Ex: NaCl, KF, CaBr 2

Ionic Bond Between atoms of metals and nonmetals with very different electronegativity Bond formed by transfer of electrons Produce charged ions all states. Conductors and have high melting point. Examples; NaCl, CaCl 2, K 2 O

Ionic 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

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 Between nonmetallic elements of similar electronegativity. Formed by sharing electron pairs Stable non-ionizing particles, they are not conductors at any state Examples; O 2, CO 2, C 2 H 6, H 2 O, SiC

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

The Convalent 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 H2OH2O

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 Formed between atoms of metallic elements Electron cloud around atoms Good conductors at all states, lustrous, very high melting points Examples; Na, Fe, Al, Au, Co

Metallic Bonds In metals, valence electrons are shared, free to move about. Metal—metal. Metals conduct electricity easily.

Metallic Bond Malleable solid. High melting point and boiling point. Insoluble in H 2 O. Insoluble in nonpolar solvents. Conducts heat and electricity. 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.

ioniccovalent valence electrons Comparison of Bonding Types sharing of electrons transfer of electrons ions molecules  EN > 1.7  EN < 1.7 high mplow mp molten salts conductive non- conductive

NaCl NaCl + - electron transfer and the formation of ions ionic bond This is the formation of an ionic bond. Cl Cl 2 covalent bond This is the formation of a covalent bond. sharing of a pair of electrons and the formation of molecules

Covalent BondsIonic BondsMetallic Bonds ShapeDefinate ShapeNo Definite Shape Definate 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