Video Transcript
Which of the following alkali metals has the greatest density? (A) Cesium, (B) potassium, (C) sodium, (D) lithium, or (E) rubidium.
Density can be defined as a measure of mass per unit of volume. In this context, density is essentially determined as the ratio of the mass number to the average atomic diameter. Density values are high when the ratio of the mass number to atomic number is high. We are looking at the density of the alkali metals. More specifically, the alkali metals we’re looking at are cesium, potassium, sodium, lithium, and rubidium. All of the alkali metals can be found in group one of the periodic table. Francium is also included as one of the alkali metals, but not hydrogen.
As we go down this group in the periodic table, we can see that the mass number systematically increases. As we descend the group, the atomic diameter also increases, but in a less predictable way. To work out how the density changes as we descend the group, we need to consider the ratio of the mass number to the atomic diameter, as the diameter determines how much volume is taken up. Both of these contributing factors increase as you descend the group, but the increase in mass number is a little more significant. In general, density increases as we descend the group.
As we are looking for the alkali metal with the greatest density, we want the atom at the bottom of the group, which is CS, cesium. So, the answer to the question “Which of the following alkali metals has the greatest density?” is (A) cesium.
