CHEM 130 Lecture Notes - Lecture 10: Electron Configuration, Isoelectronicity, Ionic Bonding
3 Oct 2018
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Lecture 10: Chapter 3 cont.
• Type of chemical bonding: Ionic
o Ionic bonding (ionic compounds):
• An atom that easily loses electrons (has a low ionization energy)
• An atom with a strong (large negative) electron affinity
• Transfer of electrons to form ions
• ions are attracted electrostatically to yield ionic compound
• Example:
▪ NaCl
• Generally a metal and a nonmetal
o Calculate the energy of interaction between ions:
• E = (2.31 x 10-19) (Q1Q2/r)
o Even among identical atoms, a bond will form if the system will have lower energy as a result
o Negative sign = attractive forces
• This means: the ion pair has lower energy than the ions alone
• Interaction between identical atoms
o Bond length: distance where the energy is lowest (minimal)
• Types of chemical bonding: Covalent
o Covalent bonding:
• Atoms forms bonds by sharing electrons
• Result: molecule
• Example:
▪ H2O
• Generally both nonmetals
• Sharing can be equal or unequal
• Polar covalent bond
o Unequal sharing of electrons between atoms in a covalent bond
o Results in partial positive and partial negative charge
o Equal sharing (covalent) = H2
o Polar covalent = HF
• What is electronegativity:
o Ability of an atom in a molecule to attract shared electrons to itself
o Linus Pauling's method to determine electronegativity:
• Delta = (H--H)act - (H--X)exp
▪ Bond energy = energy required to break a bond
▪ Shared electrons are closer to the atom X if the electronegativity of X is greater
than H
o Electronegativity increases across a period and decreases down a group
• The relationship between electronegativity and bond type
o Large electronegativity difference = most likely ionic bonding
o Intermediate electronegativity difference = most likely polar covalent bonding
o Zero electronegativity difference = covalent
• Concept check:
o If lithium and fluorine react, which has more attraction for an electron? Why?
• Fluorine
• One electron away form having a full shell
