unit 1 + 2 frq
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.
Answer: Yes, the chemist can determine which compound is in the sample. Explanation: In 1 mole of K₂O, the mass of K is 2 × 39.1 g = 78.2 g and the mass of K₂O is 94.2 g. The mass ratio of K to K₂O is 78.2 g / 94.2 g = 0.830. In 1 mole of K₂O₂, the mass of K is 2 × 39.1 g = 78.2 g and the mass of K₂O₂ is 110.2 g. The mass ratio of K to K₂O₂ is 78.2 g / 110.2 g = 0.710. If the chemist knows the mass of K and the mass of the sample, he or she must calculate the mass ratio of K to the sample. If the ratio is 0.830, the compound is pure K₂O. If the ratio is 0.710, the compound is pure K₂O₂. If the ratio is not 0.830 or 0.710, the sample is a mixture.
In terms of atomic structure, explain why the atomic radius of K is larger than that of Na.
K (potassium) has a larger atomic radius than Na (sodium) is because K has an extra electron shell compared to the Na atom. This means its valence electrons are further from the nucleus, giving K a larger atomic radius.
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.
Na (sodium) is likely to form a brittle, ionic compound with oxygen because it has similar chemical properties and is in the same group as K. The two elements are close in terms of electronegativity, which makes them good elements to form an ionic compound with Oxygen. Sodium is located in the same group as Potassium: Alkali Metals. This is because both elements have similar chemical properties. In term of their electronegativity, both elements are very close. Na has an electronegativity of 0.93, while K has an electronegativity of 0.82. This makes both ideal elements to create ionic compounds with Oxygen.
In terms of atomic structure, explain why the first-ionization energy K is less than that of Ca.
The first-ionization energy for K is less than that of Ca because K does not take much energy to remove its single outer electron. Potassium will give up its single outer electron easily in order to reach stability. There is a large increase in the second ionization energy for K compared to Ca because removal of the second electron from K is a core electron that is in a quantum shell closer to the nucleus.
