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CHEM 130 Chapter 5: Chemical Bonding I CA$9.42   Add to cart
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CHEM 130 Chapter 5: Chemical Bonding I
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  • Course
  • CHEM 130 (CHEM130)
  • Institution
  • University Of Michigan - Ann Arbor

Class notes for Chapter 5: Chemical Bonding I in the class General Chemistry: Macroscopic Investigations and Reaction Principles (CHEM 130) at the University of Michigan. Topics covered include electronegativity, bond polarity, Lewis structures, resonance, octet rule and exceptions, and VESPR theor...

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Document information

  • August 2, 2024
  • 18
  • 2022/2023
  • Class notes
  • Carol castaneda
  • All classes

Subjects

  • electronegativity
  • bond polarity
  • dipole moment
  • lewis structure
  • resonance
  • odd electron species
  • expanded octet
  • incomplete octet
  • vespr theory
  • molecular geometry

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  • University Of Michigan - Ann Arbor
  • CHEM 130 (CHEM130)
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Electronegativity and Bond Polarity
●Representing electrons with dots in the Lewis model is effective but oversimplifies the concept
○Lewis model implies that shared electrons are always equally shared
●Ex: Hydrogen fluoride
○ looks equally shared
○However in lab, when put in an electric field, H orients itself towards the negative side and F orients towards positive side
■Means that H has slight positive charge, F slight negative charge
■Represented by:
●
●δ(delta) = partial charge
○Does NOT make ionic bond – electron is still shared, just unequally
●Polar Covalent Bond: covalent bond in which atoms have different electronegativities → uneven distribution of electron density
Electronegativity
●Electronegativity: the ability of an atom to attract shared electrons toward itself in a chemical bond
●Periodic trends:
○Electronegativity increases left to right
○Electronegativity increases up a group
○Generally inversely related to atomic size
○Keep in mind from B to F, increase of 0.5 starting from 2.0; H is an outlier and has an electronegativity between B and C; biggest decrease from F to Cl and the
decrease in electronegativity between rows 1 and 2 decreases as you move left ●Linus Pauling: American chemist who discovered electronegativity and developed electronegativity values for the periodic table
●F is the most electronegative element with a value of 4.0
○Has to do with how much it PULLS electrons, not how many it actually has
Bond Polarity, Dipole Moment, and Percent Ionic Character
●Degree of polarity in a chemical bond depends on the electronegativity difference (abb. EN) 𝚫
○Greater EN = more polar bond 𝚫
○If 2 atoms with identical electronegativities form a covalent bond, they share the electrons equally in a purely covalent ( nonpolar) bond
○If 2 atoms have a large enough EN difference, the electron is transferred completely and becomes an ionic bond ●
●Dipole Moment: measure of the separation of positive and negative charge in a molecule
○Use the dipole moment to quantify the polarity of a bond
○Magnitude of the dipole moment is given by:
■
■q = magnitude
■r = distance
○Debye (D): unit used for reporting dipole moments
■1D = 3.34x10-39 C x m
■Will not be asked to calculate, but important to understand concept
○The smaller the magnitude and the smaller the distance, the smaller the dipole moment
○The larger the dipole moment, the more polar the bond
●Percent Ionic Character: ratio of a bond’s actual dipole moment to the dipole moment it
would have if the electron transferred completely from one atom to the other, multiplied by 100%
○EX: diatomic molecule w bond length of 130pm has dipole moment of 3.5D
■q = 1.6x10-19 C, r=130 pm (the approx. length of a short chemical bond)
■(1.6x10-19 C)(130x10-12m) → 2.1x10-29C x m → 6.2D
■Percent ionic character = 3.5D / 6.2D x 100% → 56%
○A bond in which an electron is completely transferred from one atom to another would have 100% ionic character
■Even the most ionic bonds don’t reach 100%
■Bonds with greater than 50% ionic character are referred to as ionic bonds
■* no need to calculate PIC but know the 50% rule – will be told if PIC is more or less than 50% and that it increases as electronegativity increases
○Generally increases as electronegativity increases
Bond Energies and Lengths
●Formation of covalent bonds release energy

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