Electron Probability Accelerated Chemistry I

Transcription

1 Introduction: Electron Probability Accelerated Chemistry I Could you determine the exact position and momentum of a baseball as it soared through the air? Of course you could by taking a timed series of snapshots of the baseball as it moved. Why then can t scientists follow a similar procedure to determine the position and momentum of an electron? You can see a moving baseball or its image because of the light bouncing off the baseball. The effect of the light on the position or the momentum of the baseball is negligible. By contrast, an electron has such an extremely small mass that light disturbs it in an unpredictable way. How can the position and momentum of an electron be determined? Knowledge of the behavior of electrons in the atom comes from the theoretical work done in the 0s by the German physicist Werner Heisenberg (0-) and the Austrian physicist Erwin Schrödenger (-). Heisenberg postulated that it was impossible to determine exactly both the position and the momentum of an electron at the same instant. Heisenberg deduced that the more certain you know the position of the electron, the less certain you are about its momentum, and vice versa. Because the exact position and momentum can never be established at any given time, the exact path of an electron through the electron cloud can never be determined. Instead the modern model of the atom, called the quantum-mechanical model, gives the probabilities of finding an electron in a particular region around the nucleus. In this investigation, you will model the probable locations of electrons around the nucleus of an atom. You will use a marble and a target to represent electrons to help you visualize regions of both high and low electron density. Materials Target circle marble ruler carbon paper Procedure:. Place the carbon paper underneath of the target circle with the carbon side up towards the target circles; lay the two sheets on the floor.. Hold the marble with your arm straight out (perpendicular from the body) and drop the marble towards the target trying to hit the center of the target. Note: you must catch the marble before it hits the target a second time.. Repeat this procedure times for a total of 00 drops.. Count the number of hits in each ring and record this number.. Measure the radius of each circle; record this number.

2 Electron Probability.doc Page Name Pre-Lab Electron Probability Accelerated Chemistry I Date Read the entire laboratory assignment and the relevant pages in your textbook. Answer all pre-lab question before beginning the lab.. What does concentric mean?. What do the marble hits represent?. What is the shape of an s orbital? What is the shape of a p orbital?. What does the Heisenberg uncertainty principle say about mapping the path of electron?

3 Data Table Ring # Distance from the center Number of hits in ring 0 Outside 0 Infinite Calculations. Calculate the area of each circle (show work): Ring # Work (Πr ) Area of complete circle (cm ) 0

4 Electron Probability.doc Page. Calculate the area of each of just the outer rings: For example the area of just ring is the area of ring minus ring, etc. You already have this for ring, so you only need to do it for rings -0. Then calculate the number of hits per unit area. Obviously since the area outside the rings is infinite you cannot do this last calculation for outside the ring. Ring # Area of ring (cm ) Marble hits/cm 0 Analysis and Synthesis. Where is the density of hits the highest? Why is this?. Density of hits: Construct a graph of hits per unit area vs. average distance from the nucleus. Attach the graph to the end of the lab.. What does this graph of the hits per unit area vs. average distance represent? Account for its shape.. Compare your density of hits with the hydrogen s electron probability density. Why is the probability of finding an electron at a particular position greatest near the nucleus?

5 Electron Probability.doc Page. Which ring has the highest probability of finding a hit (i.e. which ring has the most hits?)?. Construct a graph of the number of hits vs. average distance from the center. (Radial probability distribution).. What does the graph of the number of hits vs. average distance represent? Account for its shape.. Compare your radial probability distribution graph with Figure. in your text. What is the significance of figure.?. Is the maximum of each of your graphs the same? Explain 0. What is the radius of the 0% probability circle for your marble drops?. If you had used 00 drops instead what changes, if any, would you predict for your graphs?. Which orbital do the results of this experiment best represent?. If this experiment was representing the outermost or highest energy electron in the ground state, which element(s) could this be? Why?. Even though the Bohr model is clearly outdated and incorrect, why do you think most people persist in visualizing the atom this way as opposed to accepting the quantum mechanical model?