Presentation on theme: "Kinetic Molecular Theory & Intermolecular Forces OR KMT & IMF’s"— Presentation transcript:
1 Kinetic Molecular Theory & Intermolecular Forces OR KMT & IMF’s Chapter 13 – 2010 – Mr Nelson
2 States of MatterThe fundamental difference between states of matter is the distance between particles.
3 The States of MatterThe state a substance is in at a particular temperature and pressure depends on two variables:the kinetic energy of the particles;the strength of the attractions between the particles.
15 Intermolecular Forces (IMFs) IMF’s are found between moleculesNot between the atoms that compose the moleculeIMF’s are weaker that single, double or triple bonds
16 IMF’s IMF’s are strong enough to control physical properties such as: boiling and melting pointsvapor pressureviscosity
17 IMF’sIMF’s as a group are referred to as van der Waals forces.
18 van der Waals Forces Dipole-dipole interactions Hydrogen bonding London dispersion forces
19 Dipole-Dipole Interactions Molecules that have permanent dipoles are attracted to each other.
20 Dipole-Dipole Interactions The more polar the molecule, the higher is its boiling point.
21 London Dispersion Forces Helium has two electrons in the 1s orbital that repel each other.However, it does happen that they occasionally wind up on the same side of the atom.
22 London Dispersion Forces At that instant, the helium atom is polar, with an excess of electrons on the left side
23 London Dispersion Forces Another helium nearby, then, would have a dipole induced in it:The electrons on the left side of helium become attracted to the dipole in He atom 1
24 London Dispersion Forces London dispersion forces are attractions between an instantaneous dipole and an induced dipole.
25 London Dispersion Forces These forces are present in all molecules, whether they are polar or nonpolar.Only IMF’s present in Noble GasesThe tendency of an electron cloud to distort in this way is called polarizability.
26 Two Main Factors Affecting London Forces Molecular weightLondon forces increase with increased MW.Number of electronslarger electron clouds are easier to polarize.
27 Which Have a Greater Effect Which Have a Greater Effect? Dipole-Dipole Interactions or Dispersion ForcesIf two molecules are of comparable size and shape, dipole-dipole interactions will likely the dominating force.If one molecule is much larger than another, dispersion forces will likely determine its physical properties.
28 Boiling PointsThe nonpolar series (SnH4 to CH4) follow the expected trend.The polar series follows the trend from H2Te through H2S, but water is quite an anomaly.
29 Hydrogen BondingThe dipole-dipole interactions experienced when H is bonded to N, O, or F are unusually strong.We call these interactions hydrogen bonds.
30 Hydrogen BondingHydrogen bonding arises in part from the high electronegativity of nitrogen, oxygen, and fluorine.Also, when hydrogen is bonded to one of those very electronegative elements, the hydrogen nucleus is exposed.