The human eye contains a molecule called 11- cis -retinal that changes shape when struck with light of sufficient energy. The change in shape triggers a series of events that results in an electrical signal being sent to the brain. The minimum energy required to change the conformation of 11- cis -retinal within the eye is about 164 kJ/mol. Calculate the longest wavelength visible to the human eye.
Step 1 Elemental Astatine exists only in very tiny quantities and generally for a very short period of time due to its short half-life. Hence the bulk properties of Astatine are not known with certainity.The properties are estimated based on its periodic table position as a heavier analog of iodine and as a member of the halogen family. The general trend in state for halogens is as given below Halogen Family F(gas) Cl(gas) Br(liquid ) I(solid) At(solid) Hence there is a trend in state from gas to liquid to solid down the group. So Astatine is expected to be a solid Step 2. The element Astatine is so radioactive that large samples would melt and vaporize under the heat generated by its own radioactivity. Such behavior makes it difficult to assess whether astatine has the appropriate traits to be a metalloid. However based on its position in the periodic table it is often considered to be a metalloid. (Astatine found at the bottom of the halogen family is expected to have lesser non metallic nature when compared to the other members or can be considered to be a metalloid.)