Periodic Trends and Atomic Properties POGIL Name:

Why? The periodic table is periodic because there are regular and repeating patterns with respect to the elements on the table. These periodic trends allow one to predict products of reactions and understand how the chemical world around us works. The periodic table is one of the most important tools in all of chemistry. Knowing how to properly use and interpret the table will be one of the most valuable skills you will learn in chemistry class.

Learning Objectives: Students will discover the relationships between position on the Periodic table and electron configuration, atomic radius, ionization energy, and electron affinity.

Success Criteria:  Students will draw the electron configuration for elements  Students will relate the concepts of atomic radius, ionization energy, and electron affinity with position on the periodic table

Information Atomic Radius is the distance from the nucleus of an atom to the outermost valence electron. Ionization Energy is the energy required to remove an electron from an atom. The ionization energy refers to removing the first, outermost valence electron. Electron Affinity is the energy change that occurs when a neutral atom gains an electron. Eletronegativity is related to electron affinity, but the definition is different. Electronegativity is defined as the attraction an atom has for a shared pair of electrons, or in plain English, an atom’s desire for electrons. Hund’s Rule states that for an atom in the ground state, the number of unpaired electrons is the maximum possible and these unpaired electrons have the same spin. This means that electrons do not pair up unless they have to (meaning they would have to go up an energy level to avoid pairing up). Anion is a negatively charged ion. An atom becomes an anion when it gains one or more electrons. Cation is a positively charged ion. An atom becomes a cation when it loses one or more electrons. Task Complete the orbital box diagrams below, as illustrated for carbon, to represent the electron configuration.

1s 2s 2px 2py 2pz 1s 2s 2px 2py 2pz H C

He N

Li O

Be F

B Ne

Model 1: Electron Ionization, Detachment, and Attachment

+ - (1) X => X + e Electron Ionization ∆E1 > 0 (Positive number) - - (2) X + e => X Electron attachment ∆E2 < 0 (Negative number) - - (3) X => X + e Electron detachment ∆E3 > 0 (Positive number)

Key Questions 1. Explain what happens to an atom in an electron ionization reaction.

2. Explain what happens to an atom in an electron attachment reaction.

3. Describe how reactions (2) and (3) in Model 1 are related.

4. Should the value of the energy changes for reactions (2) and (3) be the same? Why or why not?

5. Remember that the nucleus of an atom is positive and electrons are negative. Explain why both electron detachment and ionization result in positive energy changes and electron attachment results in a negative energy change. Model 2: Electron-Electron and Electron-Nucleus Interactions in Atoms Simplified Model of Helium

2 e l e c t r o n s i n 1 s t s h e l l

Simplified Model of Lithium 2 protons in nucleus

1 electron in outer shell

2 electrons in 1s t shell

Information The diagrams in Model 2 illustrate the layers of electrons3 protons that you in nucleuswill see in multi-electron atoms. In the model of Helium, both electrons reside in the same energy level, which is the same distance from the nucleus. The nucleus is positively charged and the electrons are negatively charged, which is why the electrons in a Helium atom feel mostly love for the nucleus (Electron-Nucleus attraction). In the model of Lithium, there are 2 different levels of electrons. The outermost, or valence shell, is “shielded” from feeling the love (electron-nucleus attraction) for the nucleus by the electrons in the 1st energy level. The result is an overall feeling of hate for the electrons in the lower level (electron-electron repulsion). Key Questions 1. Are the following statements consistent with Model 2 and the Information provided? If not, explain why not for each inconsistent statement. At least one of the statements is inconsistent. a. In going from one atom to another, an increase in atomic number means that the numbers of both protons and electrons for the neutral atom must increase. b. Additional protons tend to increase the electron-nucleus attraction, increase the ionization energy, and make the atom larger. c. Additional electrons tend to increase the electron-electron repulsion, decrease the ionization energy, and make the atom larger. d. Electrons in the same shell do not shield each other from the nuclear charge very effectively, so the attraction of the nucleus dominates. 2. Based on Model 2 and the information provided with it, explain why lithium would be larger than helium. How would their ionization energies compare?

3. As the atomic number increases across a row on the periodic table, do you expect the electron-nucleus attraction to increase or decrease?

4. According to your answer the previous question, identify how the following would change as you travel across a row on the periodic table, from left to right.

a. Atomic radius b. Ionization energy c. Electronegativity

5. As the number of layers of electrons increases as you travel down the columns of the periodic table, do you expect the electron-nucleus attraction or the electron-electron repulsion to dominate? How would that affect the ionization energy?

6. Where are the most reactive elements on the periodic table? Does this relate to ionization energy?

Exercises 1. Explain why the ionization energy of sulfur is less than the ionization energy of phosphorus.

2. Explain why the ionization energy of aluminum is less than the ionization energy of magnesium.

3. For each of the following pairs, which is larger? Explain why.

a. Calcium and phosphorus b. Nitrogen and oxygen c. Copper and gold

4. For each of the following pairs, which has a larger ionization energy? Explain why.

a. Barium or cesium b. Bromine or krypton c. Silicon or carbon

5. For each of the following pairs, which has a larger electronegativity? Explain why. a. Sulfur or chlorine b. Carbon or oxygen c. Chlorine or bromine d. Nitrogen or oxygen

Reflective Questions 1. List 5 things you learned about the periodic table today.

2. Describe one concept that you completely understand and one other concept that you still don’t understand.

Group Function Reflection 1. Describe the strengths and weaknesses of your group today.