1. Bhavik Patel Chemistry AP Period: 3-4 Gangluff

2. Questions: 2 Explain each of the following observations using principles of atomic structure and/or bonding a) Potassium has a lower first-ionization energy than lithium b) The ionic radius of N 3– is larger than that of O 2–. c) A calcium atom is larger than a zinc atom. d) Boron has a lower first-ionization energy than beryllium.

3. Answer: A Potassium has a lower first-ionization energy than lithium K (1s 2 )(2s 2,2p 6 )(3s 2,3p 6 ) (3d 0 ) (4s 1 ) Z * = 19 – (10 · 1.00 + 8 · 0.85) = 2.2 Li (1s 2 )(2s 1 ) Z * = 3 - (2 · 0.35) = 2.3 Explanation not just in the difference in effective nuclear charge. As one can there is not much. The primary reason is related to the energy of a single s electron in the n = 4 level and the n = 2 level. The electron in the n = 4 level is higher in energy compared to an electron in n = 2 level and therefore is easier to remove.

4. Answer: B The ionic radius of N 3– is larger than that of O 2–. N 3– (1s 2 )(2s 2,2p 6 ) Z * = 7 – (2 · 0.85 + 7 · 0.35) = 2.85 O 2– (1s 2 )(2s 2,2p 6 ) Z * = 8 – (2 · 0.85 + 7 · 0.35) = 3.85 The electrons in N 3– experience a smaller effective nuclear charge and are less bound to the nucleus compared to the electrons in oxygen. The result is the electrons in nitrogen will take up a occupy volume.

5. Answer: C A calcium atom is larger than a zinc atom. Ca (1s 2 )(2s 2,2p 6 )(3s 2,3p 6 ) (3d 0 ) (4s 2 ) Z * = 20 – (10 · 1.00 + 8 · 0.85 + 1 · 0.35) = 2.85 Zn (1s 2 )(2s 2,2p 6 )(3s 2,3p 6 ) (3d 10 ) (4s 2 ) Z * = 30 – (10 · 1.00 + 18 · 0.85 + 1 · 0.35) = 4.35 The electrons in the 4s level experience a greater effective nuclear charge in Zn than in Ca. The electrons in Zn are therefore attracted to the nucleus to a larger extent than the electrons in calcium. So the atomic radius is smaller. In general the Z * increases more slowly across a d block compared to a p block. The reason is the electrons being added in the dblock are inside the ns electrons, while for the p block the electrons are not inside the ns electrons.

6. Answer: D Boron has a lower first-ionization energy than beryllium. Be (1s 2 )(2s 2 ) Z * = 4 – (2 · 0.85 + 1 · 0.35) = 1.95 B (1s 2 )(2s 2,2p 1 ) Z * = 8 – (2 · 0.85 + 2 · 0.35) = 2.6 We would expect from Z * arguments that it should require more energy to remove the first electron in boron compared to beryllium. However, the electron that is removed from boron in in the 2p level which is higher in energy compared to the 2s level, therefore it is easier to remove. Recall that Z * for the Group IA metals (after Li) are effectively the same value, yet we all know the first ionization energy for the valence electron in Cs is easier to remove than the valence electron in sodium because the electron is located in a higher energy level.