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).
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.
As a global Contract Research Organization (CRO), headquartered in New York, USA, Alfa Chemistry has served the pharmaceutical and biotechnology industries for eight years. Ionic Liquids
ReplyDelete