Student Exploration: Periodic Trends

Name: Date: Student Exploration: Periodic Trends Directions: Follow the instructions to go through the simulation. Respond to the questions and prompts in the orange boxes. Vocabulary: atomic radius, electron affinity, electron cloud, energy level, group, ion, ionization energy, metal, nonmetal, nucleus, period, periodic trends, picometer, valence electron Prior Knowledge Questions (Do these BEFORE using the Gizmo.) 1.​ On the image at right, the two magnets are the same. Which paper clip would be harder to remove? B 2.​ Which magnet would be most likely to attract additional paper clips? B 3.​ What is the relationship between the thickness of the book and the ability of the magnet to hold on to and attract paper clips? The thicker the book, the greater the distance between the magnet and the paper clip. This increased distance lessens the attractive force, not only causing the magnet to hold the paper clips more loosely but also decreasing the ability of the magnet to attract additional items. Gizmo Warm-up Just as the thickness of a book changes how strongly a magnet attracts a paper clip, the size of an atom determines how strongly the nucleus attracts electrons. In the Periodic Trends Gizmo, you will explore this relationship and how it affects the properties of different elements. ​ The atomic radius is a measure of the size of the electron cloud, or the region where electrons can be found. To begin, check that H (hydrogen) is selected in Group 1 on the left. Turn on Show ruler. To measure the radius, drag one end of the ruler to the proton in the nucleus and the other end to the electron. Click Save radius to record the value. 1. What is the radius of hydrogen? 53 pm Notice that the radius is measured in picometers (pm). A picometer is one trillionth of a meter. 2. On the right side of the Gizmo, select Li. Connect the right side of the ruler to the outermost electron, or valence electron. What is the radius of lithium? 167 pm Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved Activity A: Get the Gizmo ready: Atomic radius ●​ Check that Atomic radius is selected from the drop-down menu. Question: What factors affect the radius of an atom? 1.​ Predict: How do you think the radius of an atom will change as you move down a group (vertical column) in the periodic table? ​ ​ ​ ​ ​ ​ ​ ​ Predictions will vary 2.​ Collect data: Use the ruler to measure the atomic radii of the group 1 elements. As you do so, count the energy levels (shown as rings of electrons) in each atom. Record in the table. Element Number of energy levels H Li Na K 1 2 3 4 5 6 Atomic radius (pm) 53 167 190 243 265 298 3.​ Observe: What happens to the radius as you move down group 1? ​ ​ Rb ​ Cs ​ It increases 4.​ Explore: Turn off Show ruler. Select Li, and then select Be. Observe the radii of the elements in group 2. Then look at other groups. What pattern do you see? The radius tends to increase as you move down a group 5.​ Draw a conclusion: In general, what is the effect of the number of energy levels on the radius of an atom? the number of energy levels increases, the radius also increases 6.​ Predict: How do you think the radius of an atom will change as you move across a period (horizontal row) in the periodic table? ​ ​ ​ ​ ​ ​ ​ ​ decreases as you move from left to right across a period 7.​ Collect data: Beginning with Na, record the number of energy levels, number of protons, and atomic radius for each element in period 3. Element Number of energy levels Na 3 Mg 3 Al 3 Si 3 P 3 S 3 Cl 3 Ar 3 Number of protons 11 12 13 14 15 16 17 18 Atomic radius (pm) 190 145 118 111 98 88 79 71 8.​ Observe: What happens to the radius as you move across a period? ​ ​ ​ ​ Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved It tends to decrease 9.​ Explore: Investigate other periods in the periodic table. Does the same trend occur? ​ ​ Does the same trend occur? Yes Hypothesize why this trend occurs. As you move across a period, the number of protons increases while the number of energy levels stays constant. As a result, the cloud is pulled in more tightly 10.​Analyze: Consider how the number of protons might affect the size of the electron cloud. A. As you move across a period, are new energy levels added? No B. What happens to the number of protons in the nucleus as you move from one element to the next across a period? The proton number increases C. If the proton number increases while the number of energy levels remains constant, what happens to the attractive force between the nucleus and the electrons? The attractive force becomes greater D. How does your answer to the previous question explain the trend in radii across a period? The attractive force is greater across a period, while the number of energy levels is the same. Therefore, the electrons are pulled in more tightly ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 11.​Extend your thinking: The Gizmo enables you to examine ions, or atoms that have gained or lost electrons. Select Na and turn on Show ion. Compare the radius of the neutral atom to that of the ion. Repeat with Cl. Then look at other ions. See if you can find a pattern. A. Why do you think the Na+ ion is smaller than a neutral Na atom? Fewer electrons minimize electron repulsions. Since there are now more protons than electrons, the electron cloud is pulled in more tightly B. Why do you think the Cl- ion is larger than a neutral Cl atom? Increased number of electrons results in greater electron repulsions, expanding the electron cloud. Since the number of protons has remained constant, the nucleus is not able to pull in the cloud as tightly. ​ Unlike neutral atoms, ions have a different number of electrons than protons. The electrons are attracted to the protons and repelled by other electrons. If another electron is added, the repulsion between electrons increases while the attractive force of the nucleus stays the same. As a result, the electron cloud expands. Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved If an electron is lost, the cloud is pulled in more tightly. Electron repulsions decrease while the number of protons remains constant. Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved Activity B: Removing and adding electrons Get the Gizmo ready: ●​ Choose Ionization energy from the drop-down menu. Question: How does the radius of an atom affect the ability of the protons in the nucleus to hold on to and attract electrons? 1.​ Predict: Ionization energy (IE) is the energy required to remove an electron from an atom. As atomic radius increases, the valence electrons get farther from the nucleus. How do you think an atom’s size will affect its ability to hold on to its valence electrons? Why? the larger the atom, the weaker the hold on its outermost electrons ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2.​ Investigate: Select H. In the Gizmo, the hydrogen atom is shown next to a positive charge. As you move the atom to the right, the force of attraction between the positive charge and the valence electron will increase until the electron is removed. Slowly drag the atom towards the charge. After the electron is removed, use the ruler to measure the distance between the original and the final position of the electron. Record the distance and ionization energy in the table, then repeat for the other group 1 elements. Element H Distance (no units) 268 Ionization energy (kJ/mol) 1312 3.​ Analyze: What trend do you notice? ​ Li 392 520 ​ ​ Na 397 496 ​ K 414 419 ​ Rb 417 403 ​ Cs 423 376 ​ Fr 422 380 ​ Ionization energy tends to decrease down a group 4.​ Investigate: Gather data for ionization energy across a period. Record in the table below. Element Na Distance (no units) 397 Ionization energy (kJ/mol) 496 5.​ Analyze: What trend do you notice? ​ Mg Al 345 379 738 578 ​ ​ ​ Si 335 787 ​ P 286 1012 ​ S 289 1000 ​ Cl 235 1251 Ar 177 1521 ​ Ionization energy tends to increase across a period 6.​ Explore: Examine other groups and periods in the periodic table to see if the same trends exist. What trends do you see in ionization energy down a group and across a period? Ionization energy tends to decrease down a group and increase across a period Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved 7.​ Think and discuss: As you move down a group, you will recall that the radius increases. Why do you think an increase in atomic radius would result in a lower ionization energy? As the distance between the nucleus and electrons increases, the force of attraction holding electrons decreases. Therefore, it takes less energy to remove them 8.​ Think and discuss: As you move across a period, you will recall that the radius decreases. Why do you think a decrease in atomic radius would result in a greater ionization energy? As the distance between the nucleus and electrons decreases, the force of attraction holding electrons increases. Therefore, it takes more energy to remove them 9.​ Predict: Electron affinity (EA) refers to the energy released when an electron is added to an atom. This release of energy is always expressed as a negative value. The greater the magnitude of the negative value, the greater the attraction for electrons. (An EA of –100 kJ/mol would indicate a stronger attraction for electrons than an EA of –50 kJ/mol.) How do you think the size of an atom will affect its ability to attract additional electrons? smaller atoms have a higher electron affinity (EA) because the incoming electron is closer to the nucleus, leading to a stronger attraction and greater energy release 10.​Investigate: Choose Electron affinity and select fluorine (F). In the Gizmo, the fluorine atom is shown next to an electron. To measure the electron affinity, slowly drag the fluorine atom toward the electron. When the electron hops over, use the ruler to measure the distance. What is the ruler distance? 416 What is the electron affinity? -328 kj/mol 11.​Explore: Find the electron affinity for each of the other Group 17 elements and each of the other Period 2 elements. Record these below. (Note: If an atom has a positive EA it will have no attraction for an electron.) All values in the tables below will be in kJ/mol. Grp. 17 EA F: -328 Per. 2 EA Li: -60 Cl: -349 Be: 50 Br: -325 B: -27 C: -122 I: -295 N: -7 At: -222 O: -141 F: 328 Ts: -166 Ne: 120 What is the trend in EA down a group? Electron affinity tends to decrease down a group What is the trend in EA across a period? Electron affinity tends to increase across a period 12.​Think and discuss: What is the relationship between electron affinity and atomic radius? Why do you think this relationship occurs? ​ ​ ​ ​ ​ ​ ​ ​ Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved As atomic radius increases electron affinity decreases; conversely, as atomic radius decreases electron affinity increases. As atoms get smaller they tend to have a stronger attraction for electrons; as they get larger they tend to have a weaker attraction for electrons ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Activity C: ​ ​ Get the Gizmo ready: Periodic trends ●​ Select the TRENDS tab. Check that Groups is selected from the drop-down menu. Introduction: The periodic table is so named because similar patterns repeat, or appear periodically, throughout the table. These patterns are referred to as periodic trends. Question: How do atomic radius, ionization energy, and electron affinity change throughout the periodic table? 1.​ Predict: Based on your investigations in activities A and B, predict where in the periodic table you will typically find the following: Largest atoms, smallest atoms, highest ionization energy, lowest ionization energy, highest electron affinity, lowest electron affinity. Upper left region Far left column Lower left region argest atoms, lowest IE Upper right region smallest atoms, highest IE, highest EA Far right column lowest EA Lower right region 2.​ Observe: Choose Atomic radius from the drop-down menu to see the relative sizes of the elements. In which parts of the table do you find the largest and smallest atoms? The largest atoms can be found in the lower left region and the smallest in the upper right. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 3.​ Observe: Choose Ionization energy. Ionization energy is shown by color. In which parts of the table do you find atoms with the highest, and the lowest, ionization energies? The highest ionization energies are in the upper right and the lowest are in the lower left. ​ ​ ​ ​ ​ ​ ​ 4.​ Observe: Choose Electron affinity. Electron affinity is shown by color, with darker blue corresponding to the highest (most negative) electron affinity. In which parts of the table do you find the greatest and lowest attraction for electrons? ​ The highest electron affinities are in the upper right. The lowest electron affinities are in the far right column of the periodic table. The trend for EA is not as pronounced as the others. Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 5.​ Infer: Which group has high ionization energies but very weak electron affinities? ​ ​ Which group has high ionization energies but very weak electron affinities? Group 18 Why do you think this is so? Their small radius, it is difficult to remove an electron from a noble gas atom. However, since these elements have a filled octet, adding an electron would not be energetically favorable, resulting in a low EA 6.​ Investigate: Select Groups. The periodic table is divided into metals and nonmetals. Metals are to the left of the metalloids and nonmetals to the right. To the left of the table you will see a list of group names. Click on each group name to reveal its properties. A. Metals tend to have low ionization energies. What properties of elements in the metal groups do you think are the result of this tendency? Formation of + ions, good conductors, lustrous appearance, high reactivity (groups 1 and 2). B. Except for the noble gases, nonmetals tend to have high electron affinities. What properties of nonmetals do you think are the result of this tendency? Formation of negative ions, good insulators, high reactivity (esp. group 17) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 7.​ Analyze: The metallic character of an element is determined by how readily it loses electrons. Elements that lose electrons most easily have the greatest metallic character. ​ A. Which group has the greatest metallic character? Alkali metals (group 1) B. Which group has the lowest metallic character? Noble gases (group 18) C. What is the relationship between metallic character and ionization energy? Metals tend to hold electrons loosely; therefore, atoms with the lowest IE tend to have the greatest metallic character. The more metallic an atom, the more likely it is to lose electrons and form a positive ion. ​ ​ 8.​ Summarize: ✏️ Hand draw in this space or click here to select EDIT to use the drawing tool. ​ ​ ​ ​ ​ ​ Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved What conclusion can you draw about the ability of metals to hold on to and attract electrons, as compared to nonmetals? Metals have less of an ability to hold on to and attract electrons than nonmetals. Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved