Day 1 September 8
Introduction to the course. Hand out syllabus. Student seating.
Types of Particles and Some Vocabulary
Atoms are the smallest type of particle that demonstrates chemical properties. Atoms have electrons and a nucleus and are neutral or without charge.
Ions are negatively or positively charged atoms with excess number of electrons or a deficiency of electrons respectively.
Molecules are combinations of like or unlike atoms. Cl2 is a molecule of chlorine gas. So is ClBr a molecule. Molecules are held together by covalent bonds. The adjacent atoms share electrons.
Single Element is a substance that has just chemically one type of atom. All atoms have the same atomic number or the same number of protons. However elements have different isotopes with different numbers of neutrons.
A compound is a combination of two or more different types of atoms. BrCl is a compound.
Evidence that Atoms Exist
- Brownian Motion-As explained by Einstein, Brownian motion exists because of the movement of gas particles. Gas can be either molecular or atomic in motion.
- Kinetic Molecular Theory of Gas-With great success it explains how atoms or molecules in a gas give a certain pressure. The Kinetic Molecular Theory is consistent with the ideal gas laws. The basic idea is that atoms and molecules in the gas bounce against the wall of a container. Think of the walls of a balloon being the wall of a container.
The Kinetic-Molecular Theory ("the theory of moving molecules"; Rudolf Clausius, 1857)
a.Gases consist of large numbers of molecules (or atoms, in the case of the noble gases) that are in continuous, random motion with collisions at the container walls and between each other. Usually there is a great distance between each other.
b.The volume of the molecules of the gas is negligible compared to the total volume in which the gas is contained.
c.Attractive forces between gas molecules are negligible.
The Molecular picture of Pressure
- The pressure of a gas is manifested at the boundary of the vessel it is confined in, and is caused by collisions (Simulation:momentum transfer) of the molecules of the gas with the walls of the container.
- The magnitude of the pressure is related to how hard and how often the molecules strike the wall.Check out this simulation of molecules in motion in a gas.
- Field Ion Microscope and Tunneling Electron Microscope-Imaging of atoms has been accomplished. Picture of atoms have been taken.
- Law of Multiple Proportions- When two different elements react to form a series of compounds with different ratios of the different elements then they form in ratios of small whole numbers.
The Law of Multiple Proportions is the third postulate of Dalton's atomic theory. It states that for two elements which combine several ways the masses of one element which combine with a fixed mass of the second element are in a ratio of small whole numbers.
One example is CO2 and CO. Another example is H2O and H2O2. In the first example for every gram of carbon there is a certain amount x grams of oxygen in CO so that the ratio is 1:x. For CO2 there is a certain amount y grams of oxygen to every gram of carbon so that the ration of carbon to oxygen is 1:y. y is found experimentally to be twice as large as x. There isdouble the oxygen in one compound as in the other compound for each gram of carbon. The thing you need to understand was that when this was first measured no one knew the formulae for these compounds. No one knew there were such things as atoms. This type of relationship was found for many other families of compounds where each family of compounds was different combinations of the same atoms such as N, O and H, O and P, O and Pb, O. Ratios within a family were always small whole numbers when comparing masses in grams.
Carbon Monoxide / 1:x / x:y=1:2
Carbon Dioxide / 1:y
- Law of Definite Proportion- A chemical reaction always produces the same mass ratio of elements in the products of a chemical reaction no matter the amount of each reactant. Reactants are the starting materials while products are the result.
States of Matter
There are 4 states of matter in the Universe (so far). 3 of these you are familiar with: gas, liquid, and solid. The 4th is called plasma. You can form plasma in a microwave oven. Here is a video.
- Plasma-The sun is a plasma and so is anything burning. Plasma consists of mixtures of free electrons and charged positive and other types of negative particles.
You will deal strictly with the first 3 forms of matter in this class however plasma is very often used in the semiconductor industry today and in other types of manufacturing.
- Solids consist of atoms or molecules which are not free to move out of an average position but still vibrate around an average position.
- Liquids fill to the vertical walls of a container and are pourable.
- Gases fill the volume of a container whether it is a balloon or the room you are in.
Changes of State
These changes do not involve a chemical change. Only rearrangement of molecules takes place. A perfect example are the water molecules and a glass of water. At low temperatures around 0C water is frozen or a solid. As it is heated the glass of ice melts to form liquid water. While melting water is 0C but once it is totally liquefied its temperature rises as it is heated until 100C at which point it boils. As the water boils, the temperature of the liquid remains constant at 100 C. The vapor if continued to be heated increases in temperature. We have put energy into water molecules when heating from ice to vapor. The water molecule has not changed form. It is still H2O. We can reverse this process exactly by taking energy out of the vapor. This is called refrigeration as in your refrigerator.
“Heat Added” means energy added. Think of heating an ice cube on the stove.
Properties of Gases
PV=Constant’ when temperature does not change, and mass remains the same is Boyle’s law.
P/T=Constant’’ when volume is constant, and mass remains same
V/T=Constant’’’ when pressure is constant, and mass remains unchanged.
The three constants C’, C’’, C’’’ have different values.
The three equations above are explained using the kinetic molecular theory. Let’s explain the first equation known as Boyle’s law. Consider a chamber with a moveable plunger. Temperature is always the same and no new can enter the chamber. As the plunger is moved down the volume of the chamber decreases and pressure increases so the PxV stays the same. As volume decreases more collisions occur between the gas molecules and the walls of the chamber. As volume increases fewer molecular collisions occur with the wall and pressure decreases.
The second equation is explained as follows. Increasing temperature of the chamber increases pressure because the molecules speed up with temperature. Faster speeds mean more molecular collisions per second. In this case volume is not changed and no gas is allowed to enter the chamber once the experiment is started.
The third equation is true and is explained now. As we increase temperature, volume must increase since pressure is held constant or not allowed to change. Ordinarily increasing temperature of the gas would increase the rate of collisions and increase pressure. However we can keep the collision rate constant by increasing the volume. This keeps the pressure constant.
Gases are unique when considering the different states of matter. Gases fill the volume of an enclosure or container. Gases are very easily compressed. Liquids and solids hardly compress at all under an external force.
Diffusion
Gases and vapors easily diffuse. You can demonstrate gas diffusion by placing perfume at the corner of a room. After some time you will smell the perfume throughout the room. No wind should be present. The atoms or molecules bounce around at random until there is a uniform concentration of perfume in the air.
As an example consider the diagram shown below. Use a glass tube with cotton ball dipped in ammonia solution at the right and a cotton ball dipped with hydrochloric acid at the left. HCl gas is released into the tube at the left and NH3 is released into the tube at the right. Both gases diffuse toward the middle of the tube and where they meet a white powder of NH4OH is formed. Because NH3 is lighter than HCl the ammonium chloride is closest to the source of HCl since the more massive HCl only moves a short distance as compared to NH3. Light molecules diffuse more quickly than massive molecules.
Mixtures and Solutions
Watch the solution and mixture song at this link: