New version page

KU CHEM 170 - Intermolecular Forces and Phases

Type: Lecture Note
Pages: 4

This preview shows page 1 out of 4 pages.

View Full Document
View Full Document

End of preview. Want to read all 4 pages?

Upload your study docs or become a GradeBuddy member to access this document.

View Full Document
Unformatted text preview:

Chem 170 1st Edition Lecture 7Outline of Last Lecture I. Last Lecture: Ideal Gas LawII. Real Gases Have Non-Ideal BehaviorIII. Van der Walls Equation (P+n2aV2)(V −nb)=nRTIV. Joule Thompson EffectOutline of Current Lecture V. Intermolecular Forces and PhasesVI. Types of Intermolecular ForcesVII. Intermolecular Forces Affect the Behavior of SubstancesCurrent LectureCh. 12 – Liquids and SolidsIntermolecular forces are the forces between molecules and atoms. The magnitude of intermolecular forces determine whether a substance is a gas, liquid or a solid at a certain temperature. Intermolecular forces come from columbic interactions, the attractive force between positive and negative charges.Gases have the weakest intermolecular forces. In fact under the kinetic theory of gases, ideal gases do not have attractive forces between them, meaning that gases are treated as though they do not have any intermolecular forces.Liquids have slightly stronger intermolecular forces acting between molecules. Liquid intermolecular forces hold molecules together yet these molecules can move and are not in a fixed location relative to other molecules of a liquid.Solids exhibit the strongest intermolecular forces, molecules are held in place and have a fixed position relative to other molecules of the solid. This can be seen by how gases fill the shape of a container, liquids don’t fill a container, but take the shape of a container and solids do not take the shape of a container.-A phase is a form of matter that is uniform in its chemical composition and its physical state. Liquids and solids are called the condensed phase.-Cohesion refers to the forces that hold like molecules together.-Adhesion refers to the forces attract unlike molecules to each other.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Types of Intermolecular Forces:Ionic Bonding (strong) are bonds between two full charges (two ions).ex. Na+ and Cl-Van der waals interactions are interactions between molecules of pure substances.Dipole-dipole interactions are interactions between polar molecules. Polar molecule are molecules that share electrons unequally causing the molecule to have a positive region and a negative region. If there are multiple polar molecules. The negative regions would be attracted to the positive regions, thus creating intermolecular forces.For example, in HCl the hydrogen has a slight positive charge whilethe chlorine has a slight negative charge. Therefore if there were two HCl molecules the hydrogen of the first HCl molecule would be attracted to the chlorine of the second HCl molecule.Hydrogen bonding is a type of dipole-dipole interaction. However hydrogen bonding specifically involves a hydrogen bonding to a highly electronegative atom (nitrogen, oxygen or fluorine). For example, HF exhibits hydrogen bonding. The hydrogens of HF have a slight positive charge and the fluorine has a slight negative charge. Therefore if there were two HF molecules the hydrogen of the first HF molecule would be attracted to the chlorine of the second HCl molecule.Dispersion forces (also called London forces) are present in all molecules. These forces are created since, electrons are in constant motion around the molecule. Since these electrons are in constant motion they can create an instantaneous dipole (or a distribution of charge) in a molecule. This instantaneous dipole can affect the electrons of a neighboring molecule, causing the neighboring molecule to also have a dipole. Then the opposite charges of the molecules will attract one another. These forces are stronger in larger molecules, because electrons are held less tightly in large molecules. Therefore large molecules have more polarizability, which means they are more likely to have a dipole.For example, this can happen in hydrocarbons, which have no dipole and no charge.Ion-dipole interactions are the attractive forces between an ion and a polar molecule.For example, Na+ can be attracted to the negative partial charge of the oxygen in H2O.Intermolecular forces affect how substances behaveSurface tension is the measure of tightness of surface film.In liquids, molecules are pulled in every direction by the neighboring molecules by intermolecular forces and therefore are not pulled into motion in any particular direction. However the molecules at the top onlyhave molecules pulling them inward. This creates surface tension. Surfacetension allows water strider bugs to walk on top of water.The caterpillar effect occurs when water travels up a tube, because the water molecules are attracted to the molecules of the tube (adhesion). Water will climb higher up a smaller tube, because there are more water-container interactions in a smaller tube compared to larger tube.Meniscusis the curved surface of a liquid.For example, when you put water in a graduated cylinder there is a dip in the surface of the liquid; this is the concave meniscus. On the other hand,when you put mercury in a container the middle is taller than the sides; this is a convex meniscus. This is caused by intermolecular forces. The attractive forces between water molecules to other water molecules (cohesion) is weaker than the attractive forces between mercury atoms toother mercury atoms (cohesion). On the other hand, the attractive forces between water and the container (adhesion) are stronger than the attractive forces between mercury and the container (adhesion).The lotus effect occurs when a superhdrophobic surface repels water to the extent that the water beads up.Water will bead up, because the intermolecular forces between water molecules to other water molecules are stronger than the intermolecular forces between the water molecules to the molecules of the surface it is lying on. The intermolecular forces between water molecules to other water molecules pull the water molecules inward creating a sphere-like structure.Wettingout a surface occurs when water spreads out into a thin layer rather than beading up. This happens on hydrophilic (“water-loving”) surfaces.Viscosity is the resistance to flow of a liquid.If the intermolecular forces in a liquid are strong, the liquid will be more viscous (more resistant to flow). Viscosity is also temperature dependent; If the temperature is higher, then the viscosity will be lower.Solids can be crystal or amorphous. A


View Full Document
Loading Unlocking...
Login

Join to view Intermolecular Forces and Phases and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Intermolecular Forces and Phases and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?