1. Intramolecular and Intermolecular Forces

2.  Intramolecular Forces – Molecular Forces found within molecules 1)Ionic Bond (electrons transferred between metals and non-metals creates an electrostatic force) 2)Covalent Bond (electrons shared between non-metals creates a bonding force) 3)Polar Covalent Bond (electrons shared between non- metals creates a bonding force)  Intermolecular Forces - Molecular Forces found between molecules Definitions

3.  Intermolecular Forces - Molecular Forces found between molecules

4. Intermolecular http://www.youtube.com/watch?v=wYZg1j7o2x4

5.  A molecule that is slightly positively charged at one end and slightly negatively charged at the other because of electronegativity differences Polar Molecules

6. Cl H δ-δ- δ+δ+ Hydrochloric acid molecule is POLAR

7. Polar Molecules Cl C δ-δ- δ+δ+ Carbon tetrachloride molecule is NON POLAR because it lacks oppositely charged ends Cl δ-δ- δ-δ- δ-δ-

8. Some Rules for Determining Polarity of Polyatomic Molecules General Chemical FormulaPolarityExamples Diatomic: 2 different elementsPolarHCl, CO Nitrogen and 3 other atoms of the same element PolarNH3, NF3 Oxygen and 2 other atoms of the same element PolarH2O, OCl2 Carbon and other atoms of two or more elements PolarCHCl3, C2H5OH

9. Some Rules for Determining Polarity of Polyatomic Molecules General Chemical FormulaPolarityExamples Diatomic: 2 identical atomsNon- polar N2, O2 Carbon and 2 or more atoms of the same element Non- polar CH4, CO2 Polarity Practice! (a) HBr (b) NH 3 (c) C 8 H 18 (d) CH 4 (e) CH 3 OH

10. Intra molecular and Inter molecular Forces

11.  A force that holds atoms or ions together  Forces exerted within a compound (e.g. ionic and covalent bonds)  Intramolecular forces influence chemical properties of a substance  Chemical changes involve overcoming these forces in order for bonds to break and new substances to be synthesized Intramolecular Forces

12.  A force that exists between molecules or between ions and molecules to influence the physical properties of substances  These are forces of attraction and repulsion that act between molecules  Intermolecular forces include: dipole-dipole, hydrogen bonding, ion-dipole, and dispersion forces (a.k.a. London forces) Intermolecular Forces (a.ka. van der Waals Forces)

13.  Attraction between opposite partial charges of polar molecules  A polar molecule has a partial negative charge and partial positive charge – these are permanent dipoles  Polar molecules are more attracted to each other than similarly-sized non-polar molecules  Main reason for differences in melting points and boiling points for molecules Dipole-Dipole Forces

15.  A strong intermolecular attraction between molecules with a hydrogen atom that is covalently bonded to a highly electronegative atom, often oxygen and nitrogen  When a hydrogen atom is covalently bonded to a highly electronegative atom, the electronegative atom draws the electron away from the hydrogen Special Dipole-Dipole Force * Hydrogen Bonding *

16.  Because hydrogen has no electrons other than the bonding electrons, this leaves the positively charged nucleus nearly bare Special Dipole-Dipole Force * Hydrogen Bonding *

17. H 2 O (g) H 2 O (l) H 2 O (s)

18.  An intermolecular attraction between partial charges of polar molecules and ions  Can be either between cation and polar molecular or anion and polar molecule Ion-Dipole

19.  Hydration involves an ion or molecule being surrounded by water molecules that are arranged in a specific manner Hydration

21.  Consider the following diatomic molecules under standard temperature and pressure Dispersion Forces GasLiquidSolid

22.  A weak intermolecular attraction between ALL molecules, including non-polar molecules, due to temporary dipoles  Often referred to as London forces (Fritz London, 1900-1954)  Caused by non-polar molecules forming spontaneous temporary dipoles Dispersion Forces

23.  Shared electrons in covalent bonds are in constant motion  This motion, causes momentary, uneven distribution of charge  In other words, a non-polar molecule becomes slightly polar for an instant, and continues on a random basis Dispersion Forces

24.  This process “disperses” through the substance, creating fleeting dipoles that attract one another  Extremely weak and last only an instant, BUT when many interactions occur at the same time, the overall effect is significant Dispersion Forces

25.  Factors affecting magnitude of dispersion  As SIZE of a molecule increases, so do the dispersion forces, due to an increase in electrons and therefore temporary dipole formation  SHAPE of a molecule, as the area of contact increases the stronger the dispersion forces Dispersion Forces