Bonding Theory

Electronegativity

• Valence electrons are involved in chemical bonding.
• The type of bond depends on the difference in electronegativity (ΔEN) between bonding species.
• Electronegativity is the tendency for an atom to draw bonding electrons to itself.

Valance Electrons and Ions

• Valence electrons are the electrons found in the outermost shell of an atom. These are the electrons that participate in bonding
• The simplest way of determining the number of valence electrons an atom has is by looking at which group an atom is in

• Atoms will form ions by losing or gaining electrons, such that they obtain a full valence shell (full octet).
• Metals will lose electrons to form cations
• Non-metals will gain electrons to form anions
• Multivalent atoms are atoms that can form more than one stable ion. Most transition metals are multivalent

• Polyatomic ions are ions containing more than one atom

Types of Chemical Bonds

• We classify chemical bonds based on the difference in electronegativity between the atoms that form said bond

Covalent Bonds:

• Covalent bonds are bonds where electrons are shared between two non-metals

• In non-polar covalent bonds, electrons are shared equally between two of the same non-metals Examples: H2, O2, N2, Cl2

• In polar covalent bonds, electrons are shared unequally between two different non-metals
• There is a difference in electronegativity, 0 < ΔEN < 1.7. Since electrons are shared unequally in this bond, we say that there is a dipole moment

• The dipole moment is a vector with both magnitude and direction
• Partial negative charge (δ-) is assigned to the atom with the higher electronegativity
• Partial positive charge (δ+) is assigned to the atom with the lower electronegativity
• The greater the difference in electronegativity (EN), the greater the dipole moment!

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Ionic Bonds

• Are between a metal and a non-metal. You might see ionic compounds called salts like NaCl
• There is a large difference in EN (1.7 < ΔEN) in these bonds
• The metal gives electrons to the non-metal. There is a complete transfer of electrons Example: NaCl

Metallic Bonding

• The diagram below shows many atoms of a metal element surrounded by a sea of electrons that are free to move around; we say that the electrons are delocalized Examples: Aluminum, Iron, Zinc
• Conduction electrons are valence electrons that are free to move
• These conduction electrons are what give the metal their properties!
• Ductile, malleable, conduct thermal energy, conduct electricity, have luster and shine