Sinex & Gage (2006) 1CHM 101 Name___________________ Interactive Periodic Trends: A Graphical Experience This activity explores a variety of properties of the chemical elements as they vary based on position on the periodic table. You should have completed the Pre-lab Queries handout before starting this. You will need a copy of the periodic table and the interactive Excel spreadsheet available at: http://academic.pgcc.edu/~ssinex/excelets/PT_interactive. xls We will examine properties as a function of increasing atomic number in two fashions: (1) across a period and (2) down a group. The tabs as shown in the illustration below will be used to navigate the spreadsheet. The following interactive Excel features will be found on this spreadsheet. comment boxes – look for red triangles on a cell for information spinner – click on the up or down arrow to move the tracer points on the graphs option buttons - to select what data are graphed – click on button (you can only select one at a time) autofilters – click on black arrow to get a dropdown menu, select the period or group you want to plot (select all to get the full data set)Sinex & Gage (2006) 2check boxes - click on for action (you may select any number of these) hyperlink button – click for action We will explore the atomic radii, ionization energies, electron affinities, and electronegativities for the first 38 elements by atomic number. These are the elements of Periods 1 to 4 plus the first two elements from Period 5. The atomic radius or “size of an atom” can be found experimentally by dividing the distance between two nuclei of an element as measured by x-ray diffraction of the element in the solid state such as Fe (s) or Ar (s). The radii are measured in units of picometers, pm, where 1 pm = 10-12 m. The variation in the atomic radii is shown when you click on the atomic properties tab. 1. Atomic Radius or the Size of an Atom Move the tracer to identify the elements and explore their atomic sizes. Locate the beginning of each period on the plot to assist you in the questions below. Were your predictions correct on Question 1 of the Pre-lab Queries? Which is larger? Li or K F or Br Explain. Looking at the plot how would you describe the variation in atomic radius: across a period? down a group?Sinex & Gage (2006) 3Without consulting a textbook, attempt an explanation for the variation in atomic radius (remember the electron configurations): down a group across a period 2. Ionization Energy (Ionization Potential) Electrons are attracted to the nucleus due to opposite charges; hence, energy is required to remove an electron from an atom. The ionization energy, IE, is a measure of the energy for the following process: X(g) → X+(g) + e- IE1 is the designation for the first ionization energy (energy to remove the first electron). Is this an endothermic or exothermic process? Explain. For hydrogen: IE1 = 2.18 x 10-18J/atom or 1.31 MJ/mole where MJ = 106 J Verify the conversion from J/atom to MJ/mole. Show your calculations. Click on the first ionization energy option button to display the first ionization energies, IE (in units of MJ/mole). If you place the cursor on any datum point on the graph, it will display the value. The valence electrons or outermost electrons are removed first. Looking at the graph for the first thirty-eight elements, find the element with: easiest electron to remove ______ hardest electron to remove ______Sinex & Gage (2006) 4Locate the points that represent the beginning of a new period. Describe the general variation in first ionization energy: across a period down a group Locate the B Group elements (transition elements) on the graph. The B Group elements have partially filled d orbitals. Even though electrons go into a 4s orbital before the 3d, the first electron removed from the transition elements is a 4s electron. How do the first ionization energies for the Group B elements compare to each other? To the Group A elements? Successive electrons can be removed from an ion. The second ionization energy (click the button), IE2 would be given by: X+(g) → X+2(g) + e- IE2 For the second ionization energy which of the following relationships would hold? Circle your choice and explain why. IE2 < IE1 IE2 = IE1 IE2 > IE1 Plot the first and second ionization energies as a function of atomic number. In general, what can you say about the values of IE2 compared to IE1 for each element? How do the graphs of IE1 vs atomic number and IE2 vs atomic number compare to each other? Where are the peaks in each?Sinex & Gage (2006) 5Now, how do you think atomic radius and first ionization energy related? Explain you answer. Click the “Plot of 1st IE as a function of atomic radius” button to view a graph and explain what you see. Consider the ionization energy for each successive electron on an atom. You know the IE increases as the number of electrons removed increases; however, does it follow a pattern? How do you think the ionization energy changes as you remove electrons closer and closer to the nucleus? Why? Click on the electron properties tab to explore a graph of the ionization energy of all calcium electrons as a function of ionization number (# of the electron removed). Which electrons are removed first? Explain the pattern. Here are the 1s1 or core electron ionization energies for the second period elements. Element 1s1 IE Element 1s1 IE Li 11.81 N 64.36 Be 21.01 O 84.08 B 32.83 F 106.43 C 47.28 Ne 131.43 Source: Huheey et al (1993) Inorganic Chemistry: Principles of Structure and Reactivity, 4th edition Why does the energy to remove the core electron change? Would this be true for the 2s1 or 3d3 electron on any atom?Sinex & Gage (2006) 6How does this difference in energies relate to the unique atomic spectrum for each element? 3. Electron Affinity Electron affinity (EA) is usually defined as the energy released for the addition of an electron to a neutral atom as shown by the reaction below: X(g) + e- → X- (g) (usually exothermic) While removing an electron is always an endothermic process, adding an electron may be endothermic or exothermic. Why do you think this is true? If the above reaction is reversed, then the energy for the process is the energy required to remove an electron from an ion, a