1. States of Matter Chapter 13

2. Intermolecular Forces Chapter 13-2

3. “Inter” vs “Intra” “Intra” means within. “Inter” means across or between. Sports –It’s really intramural sports Within the same school –It’s interscholastic sports Across or between schools “Intramolecular forces” are ionic, covalent, metallic bonds Intramolecular forces are from molecule to molecule

4. Intramolecular Forces Intermolecular forces are very weak compared to intramolecular forces –Dispersion (or London) forces –Dipole-Dipole forces –Hydrogen bonding

5. Dispersion (or London) Forces Dispersion is an intermolecular attraction force that exists between all molecules. – These forces are the result of the movement of electrons which cause slight polar moments. –Dispersion forces are generally very weak but as the molecular weight increases so does their strength. –Most important between nonpolar molecules of the same size The cause of Bromine being liquid and Iodine being solid

6. Dispersion (or London) Forces Discoverer was Fritz London

7. Dipole-Dipole Forces Dipole-dipole forces exist between neutral, polar molecules The positive end of one molecule is attracted to the negative end of another molecule. The greater the polarity (difference in electronegativity of the atoms in the molecule), the stronger the dipole-dipole attraction. Dipole-dipole attractions are very weak Substances held together by these forces have low melting and boiling point temperatures. Generally, substances held together by dipole-dipole attractions are gases at room temperature.

8. Dipole-Dipole Forces

9. Hydrogen Bonding The positively charged hydrogen end of one molecule is attracted to the negatively charged end of another molecule Negative end must be an extremely electronegative element (fluorine, oxygen, or nitrogen - FON) Hydrogen bonds are the strongest weak bond – the H atom essentially gives its single electron to form a bond and is therefore left unshielded. The relatively strength of hydrogen bonds results in higher melting and boiling point temperatures Hydrogen bonding can explain why water is less dense in the solid phase than it is in the liquid phase (contrary to most other substances). The hydrogen bonds between water molecules in ice to form a crystal structure, keeping them further apart than they are in the liquid phase.

10. Hydrogen Bonding