Teaching Tips for Lesson 9: Ionization Energy

Transcription

1 Teaching Tips for Lesson 9: Ionization Energy Game Plan: A. Review valence electron numbers and dot notations for various element families. Review the names of the element families. B. Read text together and demonstrate ionization energy by playing Electron Escape. C. Graph ionization energies and make interpretations. D. Assign Lesson 9 practice pages. E. Give Lesson 9 Test. A. Review electron dot notations/valence electron numbers for various element families. Begin class today by reviewing how the arrangements of electrons can be utilized to see how elements are placed in various families of the periodic table. Review how members of the noble gas family each have eight valence electrons, how the halogens each have seven, the sodium family members have one and so on. Continue class by introducing the property of ionization energy by participating in the activity below! B. Demonstrate ionization energy by playing Electron Escape. To introduce the property of ionization energy play Electron Escape. All of the equipment you need is a ball - a soccer or volley ball works well. In a clear space (preferably on a carpeted or grassy area) have your students gather in a circle around you. Have them sit down while you give them instructions for play. Removing any watches or jewelry is a good idea. There are two segments to be played in the Electron Escape game. In both segments, you will initially play the roll of an atom with varying degrees of ionization energy. The ball you will hold represents a valence electron. The degree to which you 139

2 hold onto the ball while your students attempt to get it away from you is dependent upon the relative level of ionization energy that the element you represent has. In the first segment you will represent an atom with a very high ionization energy value while in the second segment you will represent an atom with a very low ionization energy value. In the first segment, explain to your students that you represent a certain element within a particular family of elements, but do not tell them which element you will be imitating. Decide initially, to yourself, that you will be a noble gas family member, neon, for example. Then, clutching the ball as tightly as you can (because noble gas family members have very high ionization energy values), give a signal to your students to attempt to react with you by removing your valence electron. Your students should try to get the ball away from you while you strongly resist. If you feel uneasy about getting physically rambunctious with your students, consider having a volunteer (dad or teacher from across the hall) play the role of the atom. After someone finally manages to remove your valence electron, ask your students if they can guess which family of elements you are representing. If they appear puzzled, remind them of the stability of the noble gas family members. Once someone correctly identifies you as a noble-gas family member, then have your students take turns trying to guess exactly which element you are representing. The person who guesses correctly can then become the next atom. This person can then represent another noble gas family member (by clutching the ball very tightly). After all players have had an opportunity to represent a noble gas family member, take the ball and now represent a member of the sodium family. Note that ionization energy values for members of the sodium family are relatively very low and therefore removing the ball from someone pretending to be sodium, for example, would be quite easy. So, in this segment of play, as soon as someone attempts to remove your valence electron, let the ball roll (or fly!) quickly to them. Question your students like in the first segment as to which family of elements you are now representing. Continue play until all students have the opportunity to be a sodium family member in the center of the circle (maybe not as exciting as a noble gas family member, but still worth the experience!). Another version of Electron Escape is more of a demonstration than a 140

3 competitive game. In this version, tell your students that you will be representing a particular element. Start with a sodium family member like potassium or sodium, for example. Have students attempt to remove your valence electron (ball). Continue by telling them that now you will be a member of the noble gas family. Then, clutching the ball very tightly, have your students attempt to remove your valence electron. When play is completed, take time to discuss the obvious differences in ionization energy that exists among families on the periodic table. Continue by referring your students to back to their text where they will now begin a graphing exercise of ionization energy. C. Graph ionization energies and make interpretations. See instructions in text. D. Assign Lesson 9 practice page. E. Give Lesson 9 Test. Note that on this test, students should not have access to a periodic table of elements. Hopefully by this time in the course, your students should be able to visualize the location of the sodium, calcium, oxygen, halogen and noble gas families. In addition, there is a bonus question on the test which asks them to list the names of all members of the noble gas family! Encourage them to read the statements on the test very carefully!. 141

4 NAME DATE FRIENDLY CHEMISTRY Lesson 9 Test: Ionization Energy Read each statement below carefully. Determine whether the statement is true or false. Depending upon your choice, write the word true or false in the blank beside the question number. Read carefully!! 1. Valence electrons are those electrons in the outermost layers of an atom. 2. Sodium family members have two valence electrons. 3. The element calcium has two valence neutrons. 4. The element bromine is a member of halogen family and has six valence electrons. 5. Sometimes atoms will lose electrons to form bonds with other atoms. The energy required to move electrons is called ionization energy. 6. Members of the noble gas family have very low ionization energy values which makes them very non-reactive. 7. Members of the sodium family have very low ionization energy values which makes them very non-reactive when compared to other elements on the periodic table of elements. 8. Lithium is a member of the sodium family and has a very low ionization energy value. This makes lithium a very reactive element. 9. Atoms of the elements oxygen and sulfur have six valence electrons. 10. All members of noble gas family have eight valence electrons and very high ionization energy values. Bonus: Without looking at a periodic table, list all members of the noble gas family: 142

5 Lesson 9: Another Trend of the Periodic Table: Ionization Energy In Lesson 8, we found that elements were grouped into families on the periodic table according to the number of valence electrons they had. We found that members of the sodium family all had one valence electron, members of the calcium family had two valence electrons and members of the oxygen family and halogen family had six and seven valence electrons, respectively. Additionally, we found that the noble gas family members had eight valence electrons (except for helium). In this lesson, we will continue to explore reasons why elements are grouped into families on the periodic table. This time we will look at a property called ionization energy. We have said that the reactivity of an element is based upon its arrangement of electrons. When we discussed electron dot notation, we learned that the electrons in the outermost orbits are called valence electrons. We also said the valence electrons were available for creating bonds with other atoms. 143 S81

6 In some cases, these valence electrons actually move to another atom to create the bond or are shared between two (or more) atoms to create the bond. The ease with which these electrons move from atom to atom is directly related to the reactivity of any element. In other words, if the valence electrons can easily be moved or transferred to another atom, that element is said to be quite reactive compared to an element in which the valence electrons cannot be easily moved or transferred to another atom. Moving or transferring electrons requires energy. The energy required to remove electrons is given the name ionization energy. Ionization refers to the creation of an ion. An ion is what an atom is called when it either loses or gains electrons in the process of creating a bond with another atom. Therefore, ionization energy is the energy required to remove an electron from an atom. Energy required to add electrons to atoms is called electron affinity. So, in addition to the degree of reactivity, the amount of ionization energy and the amount of electron affinity are two other properties by which elements are grouped into families. To better visualize this concept, let s create a graph which illustrates the varying amounts of ionization energy among the elements in the periodic table. Below is a chart which lists the relative amounts of ionization energy required to remove one electron from an atom of that particular element. On the next page is the beginning of a line graph to which the information on the chart will be transferred. Take some time and complete the graph. Note that you go down each column on the chart. Element Ionization Energy Element Ionization Energy Element Ionization Energy Hydrogen 314 Argon 363 Selenium 225 Helium 567 Potassium 100 Bromine 272 Ionization Energy Values for elements Lithium 124 Calcium 141 Krypton 323 Beryllium 215 Scandium 151 Rubidium 96 Boron 191 Titanium 157 Strontium 131 Carbon 260 Vanadium 155 Yttrium 147 Nitrogen 335 Chromium 156 Zirconium 158 Oxygen 314 Manganese 171 Niobium 159 Fluorine 402 Iron 181 Molybdenum 164 Neon 497 Cobalt 181 Technetium 168 Sodium 119 Nickel 176 Ruthenium 170 Magnesium 176 Copper 178 Rhenium 172 Aluminum 138 Zinc 217 Palladium 192 Silicon 188 Gallium 138 Silver 175 Phosphorus 242 Germanium 182 Cadmium 207 Sulfur 239 Arsenic 226 Indium 133 Chlorine 299 S82 144

7 H He Li Be Friendly Chemistry 145 S83

8 After graphing the ionization energy values of the first 49 elements, go back to your graph and find the elements that correspond to the peaks on your graph. Write those element symbols and names here: Symbol Element Name Now, look back at your periodic table of elements to find these elements. Are they in a particular family of elements with which you are familiar? To which family do they belong? Yes, they are members of the noble gas family! Based upon the ionization energy values of these elements (including xenon and radon), it can be stated that it is extremely difficult to remove an electron from an atom of a noble gas. In other words, members of the noble gas family are considered very non-reactive. The noble gases are also known as inert gases (inert meaning stable or non-reactive). Take the noble gas helium, for example. Helium, as you are probably aware, has a density which is less than the density of the gases which make up the air we breathe which is a mixture primarily of oxygen and nitrogen. This low density explains why helium-filled balloons will rise on a string. Because helium is so non-reactive, heliumfilled balloons are relatively safe for children. Helium is also used to fill airships, which are also known as blimps and dirigibles. However, this was not always the case! Let s examine the reactivity of another family of elements to find out why helium has replaced another element that was first used in airships. S84 146

9 Look back at your graph showing ionization energy of the first 49 elements. Find the lowest points (valleys) on the graph which correspond to the elements with the lowest ionization energies. Write those symbols and element names here. Symbol H Element Name Hydrogen While hydrogen may not appear to be a valley on your graph, it should be included in this family of elements. Find this group of elements on your periodic table. Which family of elements do they belong to? As a family, these elements (hydrogen, lithium, sodium, potassium, rubidium, cesium and francium) share the property of having the lowest ionization energy. This means that it takes a relatively low amount of energy to remove one electron from the outer electron orbits of atoms of these elements. In other words, these elements are by far the most reactive elements known to man! And quite a rowdy bunch of elements they are! Lets return to the history of airships. Accounts of early air travel via airship or blimp tell us that due to its low density, hydrogen gas was used to raise airships off the ground. However, hydrogen, as we have just learned, is a member of a highly reactive family of elements. Because hydrogen was used to fill the famous German-built Hindenburg airship, the airship was destroyed by fire in 1937 as it was landing at Lakehurst, New Jersey. This rigid airship had a length of 245 m (804 ft) and a gas capacity of 190,006,030 liters (6,710,000 cu ft). One-third of the Hindenburg s passengers and crew were killed in the accident. Since that time, stable helium has replaced reactive hydrogen to get blimps and dirigibles off the ground. 147 S85

10 Other members of the sodium family are also known for their high levels of reactivity. Sodium and potassium in their pure forms are so reactive that they must be stored under a petroleum product such as diesel or kerosene to prevent exposure to water vapor in the air. If sodium or potassium contact water, a violent reaction results producing strong basic compounds and hydrogen gas (the member of this rowdy bunch that we have already discussed). To summarize this lesson, you learned that valence electrons are sometimes moved from atoms in order to create bonds between those atoms. The energy it takes to do so is called ionization energy. You then created a graph of the ionization energy values and found that the families of elements shared similar ionization energy values. We looked at two families in particular and found that the noble gas family members had very high ionization energy values, meaning it takes tons of energy to remove an electron, therefore making them very non-reactive elements. On the other hand, we found that the sodium family members had very low ionization energy values making them extremely reactive. The remaining elements on the periodic table have varying degrees of ionization energy, hence they have varying degrees of reactivity associated with them. S86 148

11 149 Friendly Chemistry 1 H Hydrogen He Helium Li Lithium Be Beryllium B Boron C Carbon N Nitrogen O Oxygen F Fluorine Ne Neon Na Sodium Mg Magnesium Al Aluminum Si Silicon P Phosphorus S Sulfur Cl Chlorine Ar Argon K Potassium Ca Calcium Sc Scandium Ti Titanium V Vanadium Cr Chromium Mn Manganese Cu Copper Zn Zinc Ga Gallium Ge Germanium As Arsenic Se Selenium Br Bromine Kr Krypton Rb Rubidium Sr Strontium Y Yttrium Zr Zirconium Nb Niobium Mo Molybdenum Tc Technetium (99) 47 Ag Silver Cd Cadmium In Indium Sn Tin Sb Antimony Te Tellurium I Iodine Xe Xenon Cs Cesium Ba Barium Lu Lutetium Hf Hafnium Ta Tantalum W Tungsten Re Rhenium Au Gold Hg Mercury Tl Thallium Pb Lead Bi Bismuth Po Polonium (210) 85 At Astatine (210) 86 Rn Radon (222) 87 Fr Francium (223) 88 Ra Radium (226) 103 Lr Lawrencium (256) 104 Unq 105 Unp 106 Unh 107 Uns Noble Gas Family: very high ionization energy therefore very non-reactive. Yawn! Sodium Family: very low ionization energy therefore very high reactivity! Watch out!! S87

12 NAME DATE FRIENDLY CHEMISTRY Lesson 9 Practice Page Element Reactivity and Ionization Energy Fill in the blanks with an appropriate term. Sometimes, more than one term may be correct. In this lesson, we began with the review of electrons or those electrons found in the outermost energy levels of an atom. We discussed that members of the family have one valence electron while members of the calcium family have valence electrons. We also refreshed our memory that members of the oxygen family have valence electrons while members of the halogen family have valence electrons. We also remembered that members of the family have eight valence electrons (except for which has valence electrons). Next, we played a game where our instructor either held onto a ball tightly or hardly at all. By playing this game, we learned about which is the energy required to remove an electron from an atom. When our instructor held the ball very tightly, he/she was demonstrating ionization energy values. We learned that members of the have really high ionization energy values. This makes them very. Another name for this family is the gas family (where inert means non-reactive). Members of this family include:. When our instructor held the ball very loosely or hardly at all, he/she was demonstrating ionization energy. This means that the elements with ionization energy are very willing to with other elements. They are said to be highly. The family of elements with very low ionization energy values is the family. Members of this family include:. The family member, for example is so very reactive that it must be stored where it cannot come into contact with. Exposure to water will cause a violent reaction to occur! Another member of this family was once used to make airships float due to its low density. This family member is. But due to its high level of it is too dangerous to use. In summary, we learned that was another way elements are placed into on the periodic table. S88 150