Name: Terrell Pennington Date: 12-02-2022 Student Exploration: Periodic Trends Directions: Follow the instructions to go through the simulation. Respond to the questions andprompts 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? Answers will differ. [The distance between the magnet and the paper clip increases with the thicknessof the book. The magnet holds the paper clips more loosely as a result of the greater distance, but it isalso less able to attract other objects since the attractive force is reduced.] Gizmo Warm-up Just as the thickness of a book changes how strongly a magnet attracts a paper clip, thesize 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: Atomic radius Get the Gizmo ready: ● 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 H Li Na K Rb Cs Number of energy levels 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? It gets bigger. [Except that Cs is larger than Fr.] 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? As you descend a group, the radius tends to grow. 5. Draw a conclusion: In general, what is the effect of the number of energy levels on the radius of an atom? The radius rises along with the number of energy levels. 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? Predictions will vary. 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 Na Mg Al Si P S Cl Ar Number of energy levels 3 3 3 3 3 3 3 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. The number of protons increases but the number of energy levels remains constant as you progress through a period. Thecloud is consequently drawn in closer. 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 asyou move from one element to the next across a period? The number of protons rises. C. If the proton number increases while the number of energylevels remains constant, what happens to the attractive forcebetween the nucleus and the electrons? The attractive force becomesgreater. D. How does your answer to the previous question explain thetrend in radii across a period? While the total number of energylevels remains constant, theattracting force increases overtime. As a result, the electronsare drawn in closer. 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? Electron repulsions are reducedwith fewer electrons. Theelectron cloud is drawn closerbecause there are now moreprotons than electrons. B. Why do you think the Cl - ion is larger than a neutral Cl atom? The electron cloud grows as thenumber of electrons increasesdue to stronger electronrepulsions. The nucleus cannotdraw the cloud in as tightly sincethe number of protons hasremained constant. Unlike neutral atoms, ions have a different number of electrons than protons. The electrons are attracted tothe protons and repelled by other electrons. If another electron is added, the repulsion between electronsincreases 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 ofprotons remains constant. Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved
Activity B: Removing andadding 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 toand 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 willaffect its ability to hold on to its valence electrons? Why? The forecasts will differ. 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 willincrease until the electron is removed. Slowly drag the atom towards the charge. After the electron is removed, use the ruler to measure thedistance between the original and the final position of the electron. Record the distance and ionizationenergy in the table, then repeat for the other group 1 elements. Element H Li Na K Rb Cs Fr Distance (no units) 268 392 397 414 417 423 422 Ionization energy (kJ/mol) 1312 520 496 419 403 376 380 3. Analyze: What trend do you notice? 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 Mg Al Si P S Cl Ar Distance (no units) 397 345 379 335 286 289 235 177 Ionization energy (kJ/mol) 496 738 578 787 1012 1000 1251 1521 5. Analyze: What trend do you notice? 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? The force of attraction that holds electrons to the nucleus weakens as their distance grows.Therefore, removing them requires less effort. 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? The force of attraction holding electrons in place grows as the distance between the nucleusand electrons shrinks. Therefore, removing them requires greater energy. 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 negativevalue, the greater the attraction for electrons. (An EA of –100 kJ/mol would indicate a stronger attraction forelectrons than an EA of –50 kJ/mol.) How do you think the size of an atom will affect its ability to attract additional electrons? The forecasts will differ. 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 theelectron 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 Cl:-349 Br:-325 I:-295 At:-222 Ts:-166 Per. 2 EA Li:-60 Be:50 B:-27 C:122 N:-7 O:-141 F:-328 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? Electron affinity decreases as atomic radius grows; conversely, electron affinity increases asatomic radius decreases. Atoms tend to have a stronger attraction to electrons as they Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved
become smaller and a lesser attraction as they become larger. Activity C: Periodic trends Get the Gizmo ready: ● 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 theperiodic 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 smallest atom highest ionizations Upper right region Far left column lowest electron affinity highest electron affinity Far right column Lower left region lowest ionization energy largest atoms 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 lower left area has the largest atoms, while the upper right area contains the smallest. 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 top right and lower left have the highest and lowest ionization energies, respectively. 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 lowestattraction for electrons? Upper right has the highest electron affinities. The far right column of the periodic table hasthe lowest electron affinities. EA's tendency is not as obvious as the others'. 5. Infer: Which group has high ionization energies but very weak electron affinities? Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved
Which group has high ionization energiesbut very weak electron affinities? Group 18 Why do you think this is so? It is challenging to remove an electron from a noble gas atomdue to its short radius. Due to the filled octet in theseelements, adding an electron would not be energeticallyadvantageous, leading to 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. Clickon each group name to reveal its properties. A. Metals tend to have low ionization energies. What properties of elements inthe metal groups do you think are the result of this tendency? strong reactivity,formation of +ions, superiorconductivity, andglossy look(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 ofnegative 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 andionization energy? Atoms with the lowest IE tend tohave the most metallic charactersince metals have a tendency tohold electrons loosely. An atom ismore likely to lose electrons andproduce a positive ion the moremetallic it is. 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, ascompared to nonmetals? Compared to nonmetals, metals are less able to retain and draw electrons. Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved
