THE BASICS OF BONDING

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Salvador Dali, Galatea of the Spheres, 1952

Vocabulary:

• Coulomb’s Law
• ionic bond
• cation
• anion
• electrostatic force
• formula unit
• covalent bond
• molecular compound
• molecule
• metallic bond
• sea of electrons
• delocalized

BONDING AND �COULOMB’S LAW

Meaning:

• F is force between charges.
• q₁ and q₂ are the two charges
• r is the distance between the charges

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Consequences:

• Charge and force are DIRECTLY related
• Distance and force are INVERSELY related.

THREE TYPES OF BONDS

1. Ionic Bond: Transfer of electron(s) from a metal atom to a nonmetal atom to form oppositely charged ions that attract each other.
2. Covalent Bond: Directional sharing of electrons between two nonmetal atoms.
3. Metallic Bonds: Nondirectional sharing of electrons amongst many metal atoms.

IONIC BONDING:�METAL +�NONMETAL

The symbols for ions include the symbol for the element as well as the charge of the ion in the upper right (number first, + or – second; if charge is 1+ or 1- do not write the “1”.)

Examples:

IONIC BONDING:�METAL +�NONMETAL

• Ionically bonded ions form ionic compounds.
• Ionic compounds form a crystal lattice of alternating cations and anions.
• Representative particle: formula unit

IONIC BONDING:�METAL +�NONMETAL

According to Coulomb’s Law, what would be the consequence of:

• larger ionic charges (e.g., 1+ and 1- attraction vs. 2+ and 2- attraction?)

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• a larger ionic radius of each ion?

1+

1-

2+

2-

vs.

1+

1-

1+

1-

vs.

ION CHARGES OF THE REPRESENTATIVE ELEMENTS

1+

2+

3+

3-

2-

1-

0

The transition metals have various charges...more on this later!

These are a little tricky...more on this later!

An explanation of “why” this all occurs will come later.

• Nonmetal atoms have high electronegativities
• The + nuclei of two nonmetal atoms each have an attraction for - electrons and therefore share electrons to form a covalent bond between the atoms
• Compounds with covalent bonds are called molecular compounds
• Representative particle: Molecule

COVALENT BONDING:�NONMETAL + NONMETAL

COVALENT BONDING:�NONMETAL + NONMETAL

covalent bonds

MOLECULES VS. FORMULA UNITS

In molecular compounds (in this case H₂O), each molecule is independent and not bonded to the other molecules.

In ionic compounds (in this case NaCl), each formula unit is part of a larger, ionically bonded lattice where no pair of ions is independent.

• Metal atoms have low electronegativities
• Neighboring metallic nuclei share many electrons to form a “sea of electrons” which is the metallic bond
• Metallic bonds are non-directional meaning electrons are not shared exclusively between two atoms. The electrons are “delocalized”.
• Metallic bonds are found in:
• Elemental metals
• Mixtures of metals called alloys

METALLIC BONDING:�AMONGST METAL ATOMS

METALLIC BONDING

As a result, metals:

• Easily conduct electricity (electricity is the flow of charge in a net direction)

METALLIC BONDING

As a result, metals:

• Easily conduct electricity
• Easily conduct heat

METALLIC BONDING

As a result, metals:

• Easily conduct electricity
• Easily conduct heat
• Are malleable (can be flattened) and ductile (can be stretched into a wire)

ALLOYS

An alloy is a mixture of elements where the primary component is a metal.

There are two types of alloys we’ll discuss: substitutional alloys and interstitial alloys.

ALLOYS

Substitutional Alloys:

Atoms of one metal are substituted with another metal’s atoms that have a similar size.

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Ex: Brass (Cu, Zn)

Bronze (Cu, Sn)

ALLOYS

Interstitial Alloys:

Small atoms of a different element are trapped within a metal’s crystal matrix.

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Ex: Steel (Fe, C)