Review Questions (Answers are on Slide 4) U sing the periodic tables on the next two slides, answer the following: 1) Oxygen (O) and selenium (Se) are both Group 6 elements, but oxygen has atomic number 6, and selenium has atomic number 34. Which element has the smaller atomic size? 2) Potassium (K) is a soft metal, and Krypton (Kr) is a gas. Which element has a larger atomic radius? 3) Lithium (Li) and Fluorine (F) are both Period 2 elements. Which do you expect to have a higher ionization energy? 4) Radium (Ra) has a lower ionization energy than beryllium (Be) in Group IIA. Can you rationalize this difference in terms of the valence electron that is being removed when these elements are ionized?

Trends in Atomic Size Larger Smaller Larger

Trends in Ionization Energy Lower Higher Lower

Answers to Review Questions 1 ) Oxygen has a smaller atomic size than selenium, since the outermost electron shell for oxygen is 2p, while the outermost electron shell for selenium is 4p, which is further from the nucleus. 2) Since both potassium and krypton are Period 4 elements, and since potassium has a lower atomic number (19) than krypton (36), we expect that the electrostatic attraction of the protons in the krypton nucleus will pull the electrons inwards and shrink the krypton atom. So K is larger than Kr. 3) Fluorine (F) has a higher ionization energy than lithium (Li). Lithium has only three protons in its nucleus, while fluorine has nine protons. Since the protons attract the electrons through electrostatic force, we expect the electrons in F to be more strongly attracted to the nucleus, and a higher ionization energy than those in Li. 4) When Ra is ionized, the electron being removed is in the 7s shell, which is further from the nucleus than the 2s electron that is removed from Be when it is ionized. So we expect the energy required to ionize Ra to be lower than the energy to ionize Be.