Question

State whether true or false:
Diamond and iodine are non- metals which are lustrous.
A.True
B.False

Answer 1

Hint: The answer lies in the exception of elements. Generally non- metals are not lustrous. They vary in appearance. Think about the appearance of Diamond and Iodine. Whether they appear shiny or not, find out and you will know the answer.

Step by step answer: Basically luster is a property which is related to the reflection of light on minerals. Metallic and Non metallic are the two properties of luster. Metals have a silvery appearance or flat piece of steel.
Non metallic luster shows translucent property. You cannot see completely through the minerals. Now we will discuss the appearance of iodine and diamond. Their case is different from other non- metals.

In case of the iodine, as we go down the group the size of the atom increases which results in the low shielding of valence electrons.
Thus interaction between atoms and the outermost electron decreases. So by absorbing heat energy from light, these electrons on the surface of iodine become excited. So when they come into their normal state by releasing energy, they emit this light which appears that their surface is lustrous.

In the case of diamonds, its shiny appearance is the result of its cut, clarity, reflection and refractive index. Natural diamonds are dull and dim. Total internal refraction provides partial shine to it. The light strikes the diamond get refracted and separated into various colors. Thus provides a shine to diamond.

Thus, correct answer is option A. i.e. True.

 Note: Remember the atom’s size increases as we move down the group which results in low shielding of electrons. Due to shielding effect, effective nuclear charge is low and electrons become loose. Thus iodine is lustrous. Rough diamond has a greasy luster but proper cutting of it gives a powerful and shiny appearance.