Chemical Bonds

  • Bonds: forces that hold groups of atoms together and make them act as one unit; attraction between the nucleus of one atom and the electron of another

             ○ Bonds occur so atoms can achieve noble gas electron configuration

             ○ As the number of bonds between two atoms increases, the bond grows both shorter and stronger

                     ■ *Number of bonds is also called bond order

  • Single Bond:

             ○ 1 pair e- shared

             ○ Weaker attraction between nucleus of one atom and the bonding e-

             ○ Weaker and longer bond

  • Triple Bond

             ○ 3 pair e- shared

             ○ Stronger attraction between nucleus of one atom and the bonding e-

             ○ Stronger and shorter bond

  • What conditions will favor bond formation (Ex: H2 molecules over separate H atoms)

              ○ When the energy of the aggregate is lower than that of the separated atoms → bonds lead to lowest possible energy for a system

              ○ System will act to balance positive (repulsive) and the negative (attractive) forces

              ○ The likelihood that two elements will form a chemical bond by the interaction between valence electrons

  • Bond energy: the energy required to break a bond → tells us about the strength of a bond

               ○ If (+) → endothermic; if (-) = exothermic

               ○ Bond energies depend on the number of shared electrons between two atoms → greater bond energy suggests that a stronger double or triple bond forms

  • Forces of attraction: electron in each atom are attracted to the nucleus of the other
  • Forces of repulsion: electron-electron, proton-proton, nuclei-nuclei
  • Bond length: the distance where energy of interaction between the atoms is at a minimum

              ○ Balance between attractive and repulsive force

Coulomb’s Law:

  • States that “the strength of attraction is proportional to the magnitude of the particle charges and inversely

proportional to the square of the distance between them”

  • Opposite charges = force of attraction = (-) value; same charges = repulsion = (+) value
  • Charges are the same = force of repulsion → positive value
  • The attraction will be greater in the charged particle with the largest charge and smallest size (largest charge-size ratio)

Internuclear Distance Graphs

        ○ Element with larger atomic radius → dip more right and up

             ■ Weaker attraction/Zeff = weaker and longer bond

        ○ Shape formed because at left of dip have forces of repulsion, at right of dip have forces of attraction, and at minimum is where the forces balance themselves out, PE is lowest; stable arrangement