11.11.13 - Liquids, solids, Vapor Pressure, Lattice Energy, and Conductivity

Liquids

We had a lecture quiz on solids and liquids. Viscosity depends on the strength of the intermolecular forces. As force increases, viscosity increases. As temperature increases, the viscosity decreases. Cohesives v. Adhesive: cohesive forces happen when similar molecules bind together. Adhesive happens when intermolecular forces bind a substance to a surface. For example, water's adhesive forces between the H2O and glass are greater than the forces between the h2o molecules (creating a meniscus).

Solids

There are two groups of solids: crystalline (highly ordered arrangement) and amorphous (no particular arrangement). Covalent-Network solids, like diamonds have a high melting point and are often times hard. In order to vaporize this, the covalent bonds must be broken. Molecular solids are when atoms are held together with van der Waals forces, such as graphite. These tend to have lower melting points.

We had a lecture quiz on this to help us understand the material. We also had a worksheet called Intermolecular Forces 11 Worksheet to put together what we learned so far.

Vapor Pressure

Vapor is what we call a gaseous substance that is usually liquid at room temperature. Dynamic equilibrium occurs when the liquid molecules evaporate at the same rate as the vapor molecules condense.

Temperature affects vapor pressure. As temperature increases, more and more molecules at the surface have enough kinetic energy to escape the surface, therefore making the vapor pressure increase. When vapor pressure of a liquid reaches the atmospheric pressure, it boils. That's why water boils at a lower temperature when the elevation is high. Also, higher boiling point equals a lower vapor pressure. vapor pressure decreases with the molecular weight increases.

We had a lecture quiz to become comfortable with the material.

Lattice Energy

A quick review: There are three types of bonds. Ionic (electrostatic attraction between ions), Covalent (sharing of electrons), and Metallic (Metal atoms bonded to several other atoms. Cation surrounded by a sea of electrons). 

Lattice energy - The energy required to completely separate a mole of a solid ionic compound into its gaseous ions.

Smaller ions lead to increased lattice energy. Greater charge leads to increased energy. The effect of charge is greater than the effect of distance.

Conductivity

We worked on a small lab on conductivity. We tested several substance's conductivity. Here are the results:

We understand that in order for a substance to be conductive, there must be a sea of electrons that conduct the electricity from one wire to the other. In the case of NaCl, solids does not conduct because the atoms are in place. however, in it's liquid state, we are able to loosen the atoms and conduct the electricity through the substance.

Main Ideas

This week, I generally understand the main ideas. However, I still have trouble understanding vapor pressure and Lattice Energy. What exactly is Lattice energy, and where does it come from? What exactly is vapor pressure, what does it measure, and what are it's effects on a substance's properties? I feel quite secure on viscosity and the sea of electrons concept, however I feel I need more help on understanding the characteristics of all the other properties, such as why graphite is soft while diamonds are extremely hard.

11.4.13 - Intermolecular forces v. Intramolecular forces, and Water

Intermolecular Forces v. Intramolecular forces

This week, following out ionic and metal worksheets, we worked on understanding Intermolecular forces and intramolecular forces. Intermolecular forces are the forces between the molecules, while the intramolecular forces are between the actual atoms. For example, intermolecular forces hold together the H and O atoms in H2O, while the intermolecular forces hold together the molecules so that it stays together to form solids, liquids, or gas, depending on the temperature of the environment.

There are three types of intermolecular forces: induced dipole-induced dipole (London dispersion forces), Dipole-dipole, and Hydrogen bonding.

London dispersion force occurs between any two molecules because there is a momentary concentration of electrons on one side of the atom, causing a momentary dipole in the molecule. This is what holds molecules with no dipole moment. London dispersion force occurs in all molecules.

The next strongest intermolecular force is the dipole-dipole force. Molecules with this have attraction between the molecules due to the partial charges on the molecules from the dipole moment.

The strongest force is called the Hydrogen bond. This occurs between any molecule that has a Hydrogen atom bonded to either Nitrogen, Oxygen, of Florine atom.

To help learn the material, we went over two worksheets: Intermolecular Fores and Intermolecular Forces 1 Worksheet.

Water

We also went over a pogil about Water. We learned a little about why Salt (NaCl) dissolves in water. The hydrogen bonds override the ionic bond between the Na and Cl, breaking the ions apart. 

Main Ideas

This week, the main ideas connected because we need to know the characteristics of the intermolecular forces and intramolecular forces in order to understand why salt dissolves in water. The model with the molecules helped me because it was easy to understand which side attracted to which molecule. It also helped me understand why ice is less dense than liquid water, something I have been wondering for a very long time. I am becoming unsure, however, about the materials we covered in this weekend's lecture quizzes, "Liquids and Solids". I don't think I quite understand why liquids have surface tension.