KEY for Unit 4 - Fundamentals of Atomic Structure: Electrons in Atoms and the Periodic Table The Periodic Law - when elements are arranged according to their atomic number, their chemical and physical properties show repeatable trends. The vertical columns are called groups and the horizontal rows are called periods. There are four categories of groups (although some people do not separate the Noble gases from the Main Group elements): 1. Representative (also Main Group Elements) 2. Transition elements 3. Inner transition (also Lanthanide and Actinide) 4. Noble gasses The letters A and B in the group distinguish families: A = representative and B = transition. One of the most useful features of the periodic table is that it summarizes properties in a succinct manner. Take a look at a periodic table and think about the following. Where are metals found? See periodic table below – elements in various shades of blue. Where are nonmetals found? See periodic table below – elements in yellow. Where are the metalloids found? See periodic table below – elements in green. Are all main group elements metals, nonmetals, metalloids? All Group 1A (except H) and 2A elements are metals. In groups 3A – 8A degree of metallic character increasing down the groups (with groups 7A and 8A all being listed as nonmetals). Metalloids are in the p-block of the periodic table running in a staircase pattern from boron (B) down and to the right.. Locate the following groups in the periodic table. Alkali metals (Group 1A or simply Group 1), alkaline earth metals (Group 2A or simply Group 2), noble gases [in the past called the inert gases] (Group 8A or simply Group 18), halogens (Group 7A or simply Group 17), chalcogens (Group 6A or simply Group 16), coinage metals (Group 1B or simply Group 11), and list the semimetals [the metalloids] boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), and tellurium (Te). Polonium (Po) is often considered a metalloid, too). Check three different periodic tables and see if they all list the same metalloids. Think about why there might not be universal agreement about which elements to call metalloids (think about the definition of metalloids, or semi-metals as they are sometimes called). Metalloids are intermediate in behavior between metals and non-metals, and since metallic behavior varies across a period and up (or down) a group, we should not be surprised if there is not universal agreement on EXACTLY where the dividing line should be drawn. Some elements 61 that are listed as metalloids look quite metallic in appearance (like antimony, Sb) whereas others display properties more similar to nonmetals (example the brittle nature of silicon, Si). Figure: a reasonably current modern periodic table – new elements are added above atomic number 109, but that area of the periodic table has no naturally occurring elements. Guided Discovery Assignment 4-1 This guided discovery activity can be completed by using the information provided below. 1. Using the following list of ionization energies, IE (given in kJ per mole), prepare a graph of ionization energy (on the y-axis) vs. atomic number (on the x-axis): H, 1312; He, 2372; Li, 520; Be, 900; B, 801; C, 1086; N, 1402; O, 1314; F, 1681; Ne, 2081; Na, 496; Mg, 738; Al, 578; Si, 786; P, 1012; S, 1000; Cl, 1251; Ar, 1520; K, 419; Ca, 590; Ga, 579; Ge, 762; As, 944; Se, 941; Br, 1140; Kr, 1351 2. Make sure that you recognize that there is a jump in atomic number (from number 20 to number number 31) in the graph provided below. 3. Think about what this comparison shows. 4. On the discussion date you should be prepared to answer questions about this assignment in the classroom. 62 Highest oxidation is determined (in large part) by the number of valence electrons that are present. However, other properties (such as IE, EA, EN, and atomic size) have an influence. examples: N can become +5 (loss of 2s22p3) but F will not become +7 (it won't lose 2s22p5) but Cl will become +7 (loss of 3s23p5) DONE IN CLASS Guided Discovery Assignment 4-2 This guided discovery activity can be completed by using the information provided below. 1. Using the following list of ionization energies, IE (given in kJ per mole), see if you can relate the changes in ionizations energies of each element (from first to second to . ) to the electronic structure of that element: Ionization Energies of Several Elements Element 1st IE 2nd IE 3rd IE 4th IE 5th IE 6th IE 7th IE Na 496 4,560 Mg 738 1,450 7730 Al 577 1,816 2,744 11,600 Si 786 1,577 3,228 4,354 16,100 P 1,060 1,890 2,905 4,950 6,270 21,000 S 999 2,260 3,375 4,565 6,950 8,490 27,000 Cl 1,256 2,295 3,850 5,160 6,560 9,360 11,000 Ar 1,520 2,665 3,945 5,770 7,230 8,780 12,000 63 2. Consider how the answer to question number one relates to Guided Discovery 2 above. Think carefully about the graph of "HCON" (Highest Common Oxidation Number), shown above. 3. On the discussion date you should be prepared to answer questions about this assignment in the classroom. DONE IN CLASS 64.