Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
It’s Trendy! decreases increases The periodic table not only provides us with atomic numbers of elements and masses of elements, but it also provides us with a tool to determine general trends in chemical and physical properties. 1. Atomic Radius—the atomic radius is defined to be the decreases distance from the nucleus to the outer energy level where the outermost electrons are. The atomic radius decreases Smallest as you move from left to right across a period and increases atom as you move from top to bottom in a family. But why? For a period, you are in the same energy level which itself describes the size of the electron cloud (the area where the electrons increase increases Largest atom are most probably Largest located), so based on this elements should have the same value radius in the same period. But as you move across the period, the total positive charge in the nucleus increases thereby increasing the total force attracting the electrons in the outer energy level thereby making the cloud contract. As you go down a family it is much easier to understand Smallest value the trend. As you go down a family the energy level increases thereby increasing the radius of the cloud so the atomic radius increases. 2. Ionization Energy—this is defined as the amount of energy needed to remove an electron from the outer energy level of an atom. Here the trend is to increase from left to right across a period and to decrease from top to bottom in a family. Why? As previously stated, the size decreases as you move from left to right as the total positive charge increases. By the inverse square law (F=kQ1Q2/r2) this means the force attracting the electron increases as size decreases and as the positive charge increases. As you move from top to bottom again using the inverse square law, you get farther from nucleus thus reducing the attractive force on the electron. decreases 3. Electron Affinity—this is defined as the amount of energy required to add an electron. For all but one column this value is either negative or zero. The 2nd family is the only one that is consistently positive. Here the negative increases energy implies that energy is released rather than required when an electron is added. The trends here are exactly the Most same as for ionization energy. From left to right the energy Negative is more negative—high affinity--and from top to bottom it is Value less negative—lower affinity. The reasoning is very similar to those for ionization energy. Least Negative Value or Most Positive Value increases decreases 4. Electro negativity—this is defined as the attraction of one atom in a molecule for the shared electrons. The trend is exactly the same as for electron affinity and ionization energy. The reasoning is also the same. Fluorine is set at the highest at 4.0 and all other atoms are lower than this. 5. Reactivity—this is defined as how readily an atom reacts. For metals this is based on ionization energy where the most reactive metals are Smallest value those with the lowest ionization energies. For nonmetals this is based on electron affinity where the most negative electron affinity is the most reactive. This has to do with the fact that metals form positive ions (lose electrons) and nonmetals for negative ions (gains electrons). Largest value Materials graph paper activity series for metals and nonmetals (found in any chemistry text or on the internet) Description Note: This activity is intended to be an activity used before the students are taught the trends. It is to be used to have the students recognize the repeating patterns in the graphs. After the completion of the activity, the explanations of the trends may be addressed depending on the level of the students. Before you begin to plot data points, mark the elements on a periodic table that you will be graphing. Make sure to keep track of elements within the same group and within the same period. A color coding system or an outlining system may be helpful. Doing this will help you to answer the questions that follow. Instructions: Read Very Carefully. Each graph should take up as much of the graph paper as possible. The dots should be connected by a line using a ruler. Be sure to title and label each graph. Intervals for each graph have been given in the paragraph below. Your job is to decide the layout of your graph so it takes up most of the paper. Each property should be graphed on a separate sheet of graph paper. For the following data, plot the atomic number on the x-axis and the property on the y-axis. The intervals will be “1” . Atomic Radius: y axis range, 0-270; each interval is “10”. 1st Ionization Energy: y axis range, 0-2500; each interval is “100”. Electron Affinity: y axis range, -400 to 300; each interval is “20”. Electronegativity: y axis range, 0 – 5; each interval is “1” Element Atomic Number Atomic Radius (pm) 1st Ionization Energy (kJ/mol) Electron Affinity (kJ/mol) H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 53 31 167 112 87 67 56 48 42 38 190 145 118 111 98 88 79 71 1312 2372 520 899 801 1086 1402 1314 1681 2081 496 738 578 787 1012 1000 1251 1521 -73 0 -60 240 -27 -122 0 -141 -328 0 -53 230 -44 -134 -72 -200 -349 0 Electro negativity (Pauling Units) 2.1 NA 1.0 1.5 2.0 2.5 3.0 3.5 4.0 NA 0.9 1.2 1.5 1.8 2.1 2.5 3.0 NA Name _____________________________________________ Date ______ Block _______ Analysis 1. Based on your graphs, what is the trend in atomic radius across a period? down a family? 2. Based on your graphs, what is the trend in ionization energy across a period? down a family? 3. Based on your graphs, what is the trend in electron affinity across a period? down a family? 4. Based on your graphs, what is the trend in electro negativity across a period? down a family? 5. Using an activity series (found in your text book or the internet), what can you deduce about the relationship between ionization energy and reactivity of metals? 6. Using an activity series, what can you deduce about the relationship between electron affinity and reactivity of nonmetals? 7. Explain in 3-4 paragraphs the organization and usefulness of the modern periodic table based on what you have learned in class and what you have learned from this activity. (Paragraphs imply complete sentences.)