chemical bond

• chemical bond - “A sharing of valence electrons by atoms” (Timberlake, 2017)
  • (strong) intramolecular force
  • (weak) intermolecular forces

Intramolecular forces

• ionic bond (“completely polar bond”)

  • electrovalence

• metallic bond

• covalent bond (קשר קוולנטי, קשר שיתופי)

  • single, double or triple bond occurs when one (or two or three) pairs of electrons are shared.
  • homonuclear diatomic molecules have a covalent bond

• bond polarity:

  • “All bonds between atoms of different elements are polar to some extent.” (Jones, 2016)
  • “In reality, however, there is a continuum between the extremes of ionic and covalent bonding.” (Brown, 2012)
  • polar covalent bond (electrons are shared unequally)
    • “A bond in which there are nonzero partial charges on the atoms” (Jones, 2016)
    • “The partial charges on the two atoms in a polar covalent bond form an electric dipole”
  • non-polar covalent bond (electrons are shared equally)
    • “completely nonpolar bond occurs when the electronegativities are identical and therefore possess a difference of zero” (Wikipedia)
  • $\Delta \chi \gtrsim 1.7$ → predominantly ionic bond
  • $0.4\lesssim \Delta \chi \lesssim 1.7$ → polar covalent bond
  • $\Delta \chi \lesssim 0.4$ → nonpolar covalent bond
  • Fajans’ rules

• partial charge (or net atomic charge)

  • $\delta +$ and $\delta -$

• bond energy

• bond order

  • ”The number of electron pair bonds that link a specific pair of atoms” (Jones, 2016)

• bond length (or bond distance)

  • common unit: $\mathring{\mathrm{A}}$
  • $\text{bond length: triple}<\text{double}<\text{single}$

• isoelectronicity

Intermolecular forces

• intermolecular force (IMF)

• hydrogen bond (H-bond)

  • Dn−H···Ac
  • Dn (donor) and Ac (acceptor) are a highly electronegative atoms (specifically $\mathrm{N},\mathrm{O},\mathrm{F}$)
  • Ac has at least one lone pair of electrons
  • H is covalently bonded to Dn
  • ··· is the hydrogen bond (weaker than a covalent bond but stronger than van der Waals forces)

• van der Waals forces

  • greater if the molecules are closer
  • London dispersion force (LDF)
    • between instantaneously induced dipoles
    • the weakest of the IMFs
  • Debye force
    • permanent dipole–induced dipole
  • Keesom force
    • permanent dipole–permanent dipole

• dipole-dipole interaction

  • interactions occur between polar molecules
  • electrostatic interactions
  • between molecules which have permanent dipoles

• ion–dipole and ion–induced dipole forces

  • stronger than hydrogen bonding

References

• Timberlake, Karen C. (2017). Chemistry: An Introduction to General, Organic, and Biological Chemistry. Pearson.
• Jones, Loretta (2016). Chemical Principles. W. H. Freeman.
• Brown, Theodore L. (2012). Chemistry. Prentice Hall.