Look at the properties of the alkali metals summarized in
Table 22.2, and predict reasonable values for the melting
point, boiling point, density, and atomic radius of francium.

Question

Look at the properties of the alkali metals summarized in

Table 22.2, and predict reasonable values for the melting

point, boiling point, density, and atomic radius of francium.

Accepted Answer

Welcome back everyone. Our next problem says the table below shows some properties of alkali metals. Choose the set of values that represents the most reasonable approximates for the density atomic radius melting point and boiling point of caesium. And we have a chart with five elements that are going down the column of the alkali metals. So starting with lithium lithium sodium potassium rubidium and cesium and the values of density atomic radius melting point and boiling point for each of them. And we're asked to just find the answers that would make the most sense for each of these values for caesium the furthest one down. So let's look at each of these properties and see what the trends are over the column and then see which of our answer choices would make the most sense. So first, let's think about the property of density and we know that density is determined by mass divided by volume. So as the mass increases the density will increase, as the volume increases, the density will decrease. Well as we go down the column on the periodic table, both of these will increase the mass increasing as you add more protons and neutrons to the nucleus, the volume increasing as you add more electrons to the outer shells. However, the increase by percent in mass of our different elements is going to be greater than the increase in volume. And therefore, density will increase as you go down the column. So we're going to look at our answer choice and find the results that shows a greater density of caesium than rubidium. The one right above it. So the density of rubidium is listed as 1.532. So about 1.5 g per cubic centimeters. Choice A has a density at 1.9 g per centimeters cubed B density at 1.3 C density at 1.9 or D density at 1.3. So A and C both show a greater density for cesium. So we know that they could be possible answer choices while we'll rule out choices B and D which show a lower density for cesium, which isn't the trend we would expect. Now let's move on to atomic radius. Well, this one's pretty easy to figure out that atomic radius increases as you go down the column, as you add more electrons in outer shells, those electrons are getting further and further away from the nucleus. So the atomic radius of vidi is 248 Gers. So we're going to look for a number that is larger than 248. So choice a atomic rate is 270 B, 180 C, 270 or D 180. So again, we're looking at possible answer choices of A and C as being larger than rubidium. So it doesn't give us any new information. Let's move on to melting point. Well, melting point and boiling point have similar trends. And that's because with both the deal with disrupting the inter atomic forces as the element changes state from solid to liquid and liquid to gas. Well as that atomic radius grows greater and greater and greater, the intra atomic forces are weaker and it takes less energy to change state. So our melting point and boiling point will decrease as we go down the column. So let's take a look at our suggested melting points. Melting point of rubidium is 39.3 °C. So we're looking for a lower temperature than that choice A has a melting point of 27.0 °C. So that is lower and choice B melting 0.17 0.0 degrees. But we've already eliminated that choice. C melting 0.43 0.0 °C. So that's higher than rubidium. I'll cross that out. And in choice D melting 0.43 0.0 degrees, but we've already ruled out D so we can rule out choice C and we're down to choice A is our answer. We'll just double check that as we expect the boiling point is lower than the boiling point of Verdi. The boiling point of Verdi is 688 °C. And choice A has the boiling point at 670 °C. It is indeed lower. So our most reasonable approximate for these values for cesium is choice A with a density of 1.900 g per centimeters cubed atomic radius. 270 Peters melting 0.27 0.0 °C and boiling 0.670 °C. See you in the next video.

Look at the properties of the alkali metals summarized in
Table 22.2, and predict reasonable values for the melting
point, boiling point, density, and atomic radius of francium.

Verified Solution

Key Concepts

Alkali Metals Properties

Trends in the Periodic Table

Estimation Techniques

Look at the properties of the alkali metals summarized inTable 22.2, and predict reasonable values for the meltingpoint, boiling point, density, and atomic radius of francium.

Verified Solution

Key Concepts

Alkali Metals Properties

Trends in the Periodic Table

Estimation Techniques

Look at the properties of the alkali metals summarized in
Table 22.2, and predict reasonable values for the melting
point, boiling point, density, and atomic radius of francium.