Predict the physical properties and relative reactivity of Rb, Cs, and Fr
(From the periodic table)
You would expect the reactive to go up as you go down the table because that last outside electron is further and further away from the nucleus. Reactivity should be Li<Na<K<Rb<Cs<Fr.
Look at the melting points for
Li about 180
Na about 98
K about 63
You can see about how much the m.p. decreases as you go down the table. You might guess Rb at 40 or so and Cs and Fr less than that.
Boiling points. Again, look up the b.p. of Li, Na, and K see if there is a trend, then apply that to Rb, Cs and Fr.
To predict the physical properties and relative reactivity of Rb (Rubidium), Cs (Cesium), and Fr (Francium), we can consider their positions in the periodic table.
1. Position in the Periodic Table:
Rb, Cs, and Fr belong to Group 1, known as the alkali metals. Alkali metals are located in the far left column of the periodic table.
2. Atomic Size:
Going down Group 1, the atomic size increases due to the addition of more electron shells. Therefore, Fr has the largest atomic size, followed by Cs and Rb.
3. Reactivity:
Alkali metals are highly reactive due to their low ionization energy and their tendency to lose one electron and form a +1 cation. Reactivity increases as you go down the group because the outermost electron is further from the nucleus, making it easier to lose.
Based on these factors:
a) Atomic Size:
Fr > Cs > Rb
Francium has the largest atomic size, followed by Cesium and then Rubidium.
b) Reactivity:
Fr > Cs > Rb
Francium is expected to be the most reactive alkali metal due to its large size and low ionization energy. Cesium is less reactive than Francium but still more reactive than Rubidium. Rubidium is the least reactive among the three.
Keep in mind that Fr (Francium) is radioactive and extremely rare, so detailed experimental information about its properties is limited.