For parts of the free-response question that require calculations, clearly show the method used and the steps involved in arriving at your answers. You must show your work to receive credit for your answer. Examples and equations may be included in your answers where appropriate. Answer the following questions related to K.
(a) In terms of atomic structure, explain why the atomic radius of K is larger than that of Na.
(b) In terms of atomic structure, explain why the first-ionization energy K is less than that of Ca.
(c) K forms the compound K2O, which is an ionic compound that is brittle. Identify another element, M, that is likely to form a brittle, ionic compound with the formula M2O. Justify your answer in terms of periodic trends.
(d) The compound K2O2 also exists. A chemist can determine the mass of K in a sample of known mass that consists of either pure K2O or pure K2O2. From this information, can the chemist answer the question of which compound is in the sample? Indicate yes or no, and explain.