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1 CH 11 T12 PERIODIC TRENDS 5: 1 st IONIZATION ENERGY 1 You have mastered this topic when you can: 1) define or describe IONIZATION ENERGY. 2) describe and provide a theoretical explanation for the periodic trends among elements for IONIZATION ENERGY. 3) describe and explain the similarities and differences among elements using the periodic trends for ATOMIC RADIUS, CHEMICAL REACTIVITY and IONIZATION ENERGY. IONIZATION ENERGY I) IONIZATION ENERGY is defined as the amount of energy required to remove an electron from an atom or ion in its gaseous state. The FIRST IONIZATION ENERGY is defined as the amount of energy required to remove the most weakly held electron from a neutral atom in its gaseous state. Ionization energy is measured using these units kj/mol. II) EXPLORATION ACTIVITY 1: Discovering the periodic trends for First Ionization Energy. A) Use periodic table titled: 8. First ionization energy, electron affinity and electronegativity of the elements to draw a graph of First ionization energy versus Atomic number for the first 38 elements. Be sure to label each point with its correct symbol, each axis appropriately and give the graph a title. Complete the Analysis (creating empirical knowledge) and Synthesis (creating theoretical knowledge). Be sure to use a pencil to draw your graph and your answers for the Analysis and Synthesis as you may want to adjust your answers. 1. Analysis: Describe any periodic trends you detect. (There are two periodic trends.) 2. Synthesis: Suggest explanations for each periodic trend.

2 CH 11 T12 PERIODIC TRENDS 5: 1 st IONIZATION ENERGY 2 B) There are two trends for first ionization energy, MEMORIZE THEM!! 1) AS THE ATOMIC NUMBER INCREASES WITHIN A GROUP (TOP TO BOTTOM), THE FIRST IONIZATION ENERGY TENDS TO DECREASE. 2) AS THE ATOMIC NUMBER INCREASES WITHIN A PERIOD (LEFT TO RIGHT), THE FIRST IONIZATION ENERGY TENDS TO INCREASE. III) EXPLORATION ACTIVITY 2: Explaining the periodic trend for first ionization energy within groups. A) In this activity you will use your knowledge of the periodic trends studied thus far to explain the periodic trend for first ionization energy within groups. INSTRUCTIONS: Draw orbital diagrams for the first three elements in Group 2, the alkaline earth metals, then answer the questions below. 1. State the trend for the first ionization energy as the atomic number 2. Describe how the atomic radius changes as the atomic number 3. Describe how the shielding effect changes as the atomic number 4. Describe how the attraction between the nucleus and valence electrons changes as the atomic number 5. Describe how the energy required to remove the first valence electron changes as the atomic number 6. Write a theoretical explanation for the first ionization energy trend down a group. PLEASE USE NUMBERED POINT OR BULLIT FORM.

3 CH 11 T12 PERIODIC TRENDS 5: 1 st IONIZATION ENERGY 3 B) THEORETICAL EXPLANATION OF THE FIRST IONIZATION ENERGY TREND WITHIN A GROUP 1) THE TREND: As the atomic number increases down a group, the first ionization energy tends to decrease. 2) The decrease in first ionization energy as atomic number increases down a group is explained using the theoretical reasoning outlined below. a) THE EXPLANATION FOR THIS TREND: As the atomic number increases down a group, the first ionization energy decreases because as the Atomic radius increases 2. the shielding effect increases, and 3. the attraction between the nucleus and valence electrons decreases, which 4. decreases the amount of energy required to remove the first valence electron. IV) EXPLORATION ACTIVITY 3: Explaining the periodic trend for first ionization energy within the periods. A) In this activity you will use your knowledge of the periodic trends studied thus far to explain the periodic trend for first ionization energy within the periods. INSTRUCTIONS: Draw orbital diagrams for the first three elements in period 3, then answer the questions below. 1. State the trend for the first ionization energy as the atomic number increases left to right across a period. 2. Describe how the atomic radius changes as the atomic number increases left to right across a period. 3. Describe how the shielding effect changes as the atomic number increases left to right across a period. 4. Describe how the attraction between the nucleus and valence electrons changes as the atomic number increases left to right across a period. 5. How do the changed in the shielding effect and the attraction between the nucleus and valence electrons as the atomic number increases left to right across a period compare to each other. 6. Describe how the energy required to remove the first valence electron changes as the atomic number 7. Write a theoretical explanation for the first ionization energy trend left to right across a period. PLEASE USE NUMBERED POINT OR BULLIT FORM.

4 CH 11 T12 PERIODIC TRENDS 5: 1 st IONIZATION ENERGY 4 B) THEORETICAL EXPLANATION OF THE FIRST IONIZATION ENERGY TREND WITHIN A PERIOD 1) THE TREND: As the atomic number increases moving left to right across a period, first ionization energy to increase. 2) The increase in first ionization energy left to right across a period is explained using the theoretical reasoning outlined below. a) THE EXPLANATION FOR THIS TREND: As atomic number increases left to right across a period, first ionization energy tends to increase because as the Atomic radius decreases 2. the shielding effect increases, while 3. the attraction between the nucleus and valence electrons is increasing more, which 4. increases the amount of energy required to remove the first valence electron. EXPLORATION ACTIVITY 2 from page 2 ANSWERS TO THE EXPLORATION ACTIVITIES 1. As the atomic number increases down a group, the first ionization energy decreases. 2. As the atomic number increases down a group, the atomic radius increases. 3. As the atomic number increases down a group of metals, the shielding effect increases. 4. As the atomic number increases down a group of metals, the attraction between the nucleus and the valence electrons decreases. 5. As the atomic number increases down a group, the energy required to remove the first valence electrons decreases. 6. i.e. The first ionization energy decreases as the atomic number increases moving down a group because 1. As the Atomic Radius increases 2. the shielding effect increases, and 3. the attraction between the nucleus and the valence electrons decreases, which 4. decreases the energy required to remove the first valence electron. EXPLORATION ACTIVITY 2 from page 3 1. As the atomic number increases left to right across a period the first ionization energy increases. 2. As atomic number increases left to right across a period the shielding effect increases. 3. As atomic number increases left to right across a period of metals the shielding effect increases. 4. As the atomic number increases left to right across a period the attraction between the nucleus and the valence electrons increases. 5. As the atomic number increases left to right across a period the attraction between the nucleus and the valence electrons increases more than the shielding effect. 6. As the atomic number increases left to right across a period, the energy required to remove the first valence electron increases. 8. i.e. As the atomic number increases left to right across a period, the first ionization energy increases because 1. As the Atomic Radius decreases 2. the shielding effect increases, while 3. the attraction between the nucleus and the valence electrons increases more, which 4. increases the energy required to remove the first valence electron.

5 CH 11 T12 PERIODIC TRENDS 5: 1 st IONIZATION ENERGY 5 ASSIGNMENT At the top of your assignment, please print T12 Periodic Trends 5: 1 st Ionization Energy, your LAST then First name, block and date. Complete these questions in the order given here. [Marks indicated in italicized brackets.] USE POINT OR BULLIT FORM WHEN EXPLAINING PERIODIC TRENDS. 1. State then provide a theoretical explanation for each of the two first ionization energy trends within the periodic table. [10] 2. Use your knowledge of the periodic trends to list the elements below in increasing order of first ionization energy. Provide a theoretical explanation for your arrangement. [5] S, Al, K, Mg, Sr 3. A chemistry student makes this hypothesis: The first ionization energies of two isotopes of oxygen are different. State whether you agree or disagree with this hypothesis? Justify your answer using your knowledge of atomic structure. [3] 4. Describe the relationship between atomic radius, chemical reactivity and first ionization energy and within a group of metals. [3] 5. Describe the periodic trends for atomic radius, chemical reactivity and first ionization energy and within a period of non-metals are similar. Not the explanations. [3] [24 marks in total] BRING GRID PAPER NEXT CLASS!!