I. Introduction to Atomic MicroscopeRunning the programRevised 1/08,8/05 SHMTMAtomic MicroscopeSimulating Aatomic Bbehavior on the Ccomputer:Physical Behavior of GasesChemists characterize changes in matter as either physical or chemical. Most people have extensive experience in physical changes (also called “changes of state”): icemelting is an example of a solid changing to a liquid; boiling water is an example of a liquid changing into a gas. These changes are called “physical changes” because new compounds are not formed; that is, freezing and then melting water produces no new compounds. In contrast, chemical changes involve the transformation of compounds, in which reactant compounds are consumed and new product compounds are formed. For example, the changes involved in the interaction of liquid water and sodium metal are chemical because new compounds are formed as a result of the change: in this case, water is changed into hydrogen gas and hydroxide ions, and sodium atoms into sodium ions.In the series of “computer experiments” below, you will explore what is changing on the “atomic scale” during physical changes. The goal of the lab is to provide you with a picture of how atoms behave, and how physical changes observed in the world are explained using atomic scale models. It is hoped that the experience helps you develop a picture of physical and chemical changes. You are then asked to apply your improved understanding to predict how the atoms would respond in new situations.The computer simulation (“Atomic Microscope”) applies current models of how atoms behave in a pictorial way. That is, the program does not just show a bunch of balls bouncing around – the relationships that you will be exploring are based on science’s bestunderstanding of matter to date. As with all simulations, there are places where the simulation fails due to limitations.I. Introduction to Atomic MicroscopeExperiment Group FreeplayExperiment Title --(Large Population)Running the programTo run the program from a PC (running Windows XP Professional) - go to:Start/All programs/Departmental/Chemistry/Atomic MicroscopeStart by running a 2D version of the program (we examine 3D views later). What each icon does can be seen by placing (not clicking) the cursor over a control; its name/function appears in the menu bar at the upper right. For example, when the cursoris placed over the blue/white/red slider, the program tells you that this controls temperature.A) Program Control - The four icons at the upper left are Home (main screen), Controls, Information, and Services. We will toggle back and forth between Home and Controls, and occasionally select a saved state found in Information for a given experiment. The ESC key will exit the program at any point.B) Experiment Controls – Looking at experiment controls (the icons at the lower right) the top row of icons (from left to right) are Interatomic Potential, Classical Notation, Clear Experiment (or Reset), and Save States 1-3. The blue/white/red slider below the first row of icons controls the temperature. The next row of icons control number and type of atoms in the box. The bottom two controls are a Pause button and a Time Periods per Update slider.1] Experiment Controls: Atoms - The program will let you add up to 250 He, Ne, Ar, or Kr atoms to the “volume”. Start by adding 25 Kr atoms: double-click the number 0 below the Kr atom and type in 25 or just click and hold the up arrow for Kr. What does Classical Notation do? If you got the program to an especially interesting state, you could save the entire experiment as a Saved State, but we won’t need to do this.Wait for the atoms to distribute throughout the volume, click (turn on) InteratomicPotentials and explore what happens as you lower the temperature to its coldest. Return to the Main screen (click the Home icon) and choose the “3D” Experimentfrom the “Freeplay” Experiment Group. Add 100 Kr atoms and turn on Interatomic Potentials. Observe again how the atoms behave as you adjust the temperature.2] Experiment Controls: Program Speed - The Pause button on the bottom row can be used to stop the program and observe atom distribution, but you can also change settings (temperature, atom number or type, program speed, etc.) while the program ispaused; changes take effect immediately when you resume. We will make use of this feature throughout the lab.The bottom slider essentially controls program speed, but it sometimes appears that it is controlling temperature. Specifically, the program calculates what happens to each atom during an incremental “time step”, but doesn’t necessarily display the change after every step. You can control how many time steps the program calculates between display updates using the bottom slider. Try pushing the slider to the right. Notice that the atoms move faster, just as if you increased the temperature. It’s important to understand that the temperature has not increased; the bottom slider only controls how often atom positions on the screen are redisplayed or updated.To illustrate the difference, try the following: clear the display, push the temperature slider to its coldest and add 100 Kr atoms. Notice that the atoms barely moveaway from the edge of the box. Push the speed slider to its fastest - the atoms are now Atomic Microscope-2moving faster not because the temperature was increased, but because the program is running faster.Now turn on Interatomic Potentials, adjust the program speed and temperature until the atoms coalesce into two or three clusters, then lower the temperature to its coldest. Adjust the speed slider throughout its entire range - notice that the cluster does not come apart. Next set the speed to ~1/2 and increase the temperature into the white zone. Notice that changes in temperature lead to new behavior (the cluster comes apart), not just faster atom motion, because temperature affects how the atoms move; the program speed does not.In the following section, you are asked to make observations about gaseous atoms using the simulation, record relevant data, suggest explanations for the observed behavior (that is, come up with a story to explain what is happening), and in some cases propose a test that could be done to help determine if your explanation “works”.Although you may not realize it, the above paragraph is a description of how all science is done.