Final answer:
The order of the elements in decreasing electron affinities is F (fluorine), O (oxygen), Co (cobalt), Li (lithium), Na (sodium), and Rb (rubidium), with fluorine having the most negative electron affinity and rubidium the least.
Step-by-step explanation:
To arrange the elements Co (cobalt), O (oxygen), Li (lithium), Na (sodium), Rb (rubidium), and F (fluorine) in order of decreasing electron affinities, we need to consider the periodic trends. Generally, electron affinity increases across a period (from left to right) and decreases down a group (from top to bottom) in the periodic table. However, keep in mind that the electron affinities can vary due to the specific electronic configurations of elements. With this in mind, we predict the following order:
- F (fluorine)
- O (oxygen)
- Co (cobalt)
- Li (lithium)
- Na (sodium)
- Rb (rubidium)
Fluorine has the most negative electron affinity since it is the halogen in the top-right position of the elements listed, followed by oxygen which is also in the same period to the left. Cobalt, being a transition metal, has a lower electron affinity than oxygen. Lithium and sodium, belonging to the alkali metals, have lower affinities due to being in the s-block. Lastly, rubidium has the least negative electron affinity, as it is positioned at the bottom of the alkali metal group.