University:
Central Michigan University
Course:
CHM 331 | Inorganic Chemistry
Academic year:

2022
Views:

141

Pages:

4
Author:

tedeschimlg

ChemQuest 16 Trends in Size Name: Κεν Date: Hour: Information: Shielding FIGURE 1: "Bohr Diagrams" of boron, carbon and nitrogen nucleus charge = +5 Boron nucleus charge = +6 Carbon nucleus charge = +7 Nitrogen Because the nucleus is positively charged, it exerts an attractive force on the electrons. However, the three electrons in boron's outer energy level do not feel the full +5 attraction from the 5 protons in boron's nucleus. Before the +5 attraction gets to the outer energy level it gets partially cancelled (or "shielded") by the two electrons in the first energy level. The two electrons in the first energy level weaken the attractive force by two. Therefore to the outer energy level it only "feels" like a +3 charge rather than a +5 charge from the nucleus. Consider the diagram of carbon. An electron in the outer energy level only "feels" a charge of +4 coming from the nucleus because the two electrons in the first energy level shield two of the positive charges from the nucleus. Critical Thinking Questions 1. How large is the charge that the second energy level of nitrogen "feels" from the nucleus? +5 2. Why does the first energy level in each of the three above diagrams only contain two electrons? Is (2 e can fit in it) 3. How many electrons can fit in the second energy level of any atom? 8 4. How many clectrons can fit in the third energy level? 18 5. How many energy levels does aluminum have? How many electrons should be in each energy level? 13 Ist-2 2nd-8 3rd-3 6. Draw a Bohr diagram for aluminum similar to those above. 7. Explain why the second energy level of aluminum only feels a +11 attraction instead of a +13 attraction from aluminum's electrons. the 2 e in the first energy level "shield" 2 of the positive charges 8. How large is the charge that the third energy level of an aluminum atom "feels" from the nucleus? +3 Information: Charge and Distance As you know, opposite charges attract. Examine the following diagrams of charged metal spheres. FIGURE 2: Diagram A Diagram B Diagram C +3 -3 +4 4 +5 -5 The attraction between the two charged metal spheres in cach diagram is represented by an arrow. The metal spheres are pulled closer together in diagram C because of the +5 to 5 attraction is stronger than the +4 to -4 attraction in Diagram B and the +3 to -3 attraction in Diagram A. Electrons behave the same way as the metal spheres are depicted in Figure 2. Consider the Bohr diagrams of boron, carbon and nitrogen in Figure 1. Recall that Boron's outer electrons feel a +3 attraction from the nucleus. Carbon's outer electrons feel a +4 attraction. In question 1, you found out that nitrogen's outer electrons feel a +5 attraction. This attraction between the nucleus and outer energy level determines the size of the atom. If the attraction is strong the atom is small; if the attraction is weak, the atom spreads out and is larger. Critical Thinking Questions 9. Which atom is larger: nitrogen or carbon? Why? Carbon. nitrogen has bigger charges SO a greater attraction 10. In a silicon atom, the force of attraction from the nucleus to the outer energy level is 44. Using a Bohr diagram of a silicon atom as an illustration, explain in detail why this is true. 10e in the first 2 energy levels shield the +14 charge 11. Draw Bohr diagrams for sulfur and chlorine.

Chem Bohr Diagrams Key

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