LESSON 4

• KINETIC MOLECULAR THEORY 


  JOHANNES DIEDERIK VAN DER WAALS 1873 - 1923 - Dutch Physicist, winner of the 1910 NobelPrize for Physics for his research on the gaseous and liquid states of matter.
• KINETIC MOLECULAR THEORY 


  JOHANNES DIEDERIK VAN DER WAALS 1873 - 1923 - Van der Waals force, named after him.
• KINETIC MOLECULAR THEORY 


  JOHANNES DIEDERIK VAN DER WAALS 1873 - 1923 - A force of attraction between two nonpolar substances. Molecules can attract each other at moderate distances and repel each other at close range.
• DIPOLE - DIPOLE FORCES - It exists between polar molecules. Polar molecules possess a permanent dipole moment. It is attributed to the electronegativity difference. When 2 polar molecules are brought together, the partial positive charge of one molecule will be attracted to the partial negative charge of the neighboring molecule.
• DIPOLE - INDUCED DIPOLE FORCES - It is an interaction between nonpolar and polar molecules. When there is a polar molecule, a nonpolar molecule is forced to become a dipole. During the interaction, some of the electrons of the nonpolar molecule become distributed on one side(distorted).
• DIPOLE - INDUCED DIPOLE FORCES


  (a) An isolated oxygen molecule has no dipole; its

  electrons are distributed evenly. (b) An adjacent

  water molecule induces a redistribution of

  electrons in the oxygen molecule. (the slightly

  negative side of the oxygen molecule is shown as

  larger than the slightly positive side because the

  slightly negative side contains more electrons.)
• HYDROGEN BONDS - It is a special type of dipole - dipole

  interaction that only exists in molecules containing a hydrogen atom bonded to a highly electronegative atom such as N,O, and F. Hydrogen bonding is about 5 - 10x stronger than other dipole - dipole interactions.
• ION - DIPOLE FORCES - It acts between an ion (either a cation or anion) and a polar molecule. The degree of

  the interaction depends on the size and charge of the ion and the size and dipole moment of the polar molecule.
• ION - DIPOLE FORCES


  Positive ends of polar molecules are oriented toward negatively charged anion
• ION - DIPOLE FORCES


  Negative ends of polar molecules are oriented toward positively charged cation
• ION - INDUCED DIPOLE FORCES - It exists

  between an ion approaching a nonpolar molecule.
• LONDON DISPERSION FORCES (DISPERSION FORCES)


  This was explained by Fritz London who is a German - American physicist. It exists between all atoms and molecules. This force governs the nonpolar molecules.
• LONDON DISPERSION FORCES (DISPERSION FORCES)


  Though containing symmetrical electrons on both sides, the molecule can momentarily acquire a non-uniform electron density called an instantaneous

  dipole(temporary dipole). It is an interaction between an instantaneous dipole and an induced dipole.
• LONDON DISPERSION FORCES (DISPERSION FORCES)


  Examples include H2, Br2, Cl2, F2, O2 ,N2, CH4, C2H6, and CCl4