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 The type of bond can usuallyusually be calculated by be calculated by finding the difference in electronegativity of the finding the difference in electronegativity of the

two atoms that are going together.two atoms that are going together.This table is found on page 304 of the text.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: NaClNa = 0.8, Cl = 3.0Difference is 2.2, sothis is an ionic bond!

Bonding spectrum100% covalent 100% ionic

A+ B-A B A B

Increasing EN

Increasing polarity Transfer

IONIC BONDbond 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 CharacteristicsCrystalline solid.Very high melting point.Soluble in H2O.Insoluble in nonpolar solvents.Nonconductor of heat and electricity in solid form.Conducts electricity in aqueous solutions or when melted.Examples: NaCl, CaCO3

Ionic Bond

COVALENT BONDbond 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 H2OSoluble 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

H2 or Cl2

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 BONDbond found in

metals; holds metal atoms together

very stronglyMetal + 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 H2O.• 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 transferand the formation of ions

This is the formation of an ionic bondionic bond.

This is the formation of a covalent bondcovalent bond.

Cl2

Cl Cl

sharing of a pair of electronsand 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 Bonds Ionic Bonds Metallic Bonds

Shape Definite Shape No Definite Shape

Definite Shape

Boiling Point Low High High

Examples Methane (CH4) Sodium Chloride (NaCl)

Iron Metal

Occurs Between 2 Non-Metals Metal and Non-metal

2 Metals

Formation Sharing of Electrons

Transfer of Electrons

The valence electrons are detached from the atoms but not held by any of the

other atoms.

Polarity Low High ----------

Melting Point Low High High

Electronegativity Difference

Low High Low

State at Room Temperature

Liquid Or Gaseous

Solid 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