At the molecular level, I would like to know fundamentally how does a vitamin differs from a mineral. I understand both have, to say, Fe (Iron), then what exactly makes it a mineral Iron or a vitamin Iron. Does the properties of Iron changes from Vitamins to minerals?
Since you are asking about vitamins vs. minerals, I assume what you mean by mineral is a "dietary mineral" (as opposed to the more typical meaning of mineral, which is a naturally-occurring inorganic compound). So:
A dietary mineral is an element that is essential for life (e.g., K, Ca, Fe, Se, Cr, P, I, Cl, Mo, etc.), and is required in small quantities. This rules out C, H, O, and N which are essential for life in large quantities as part of carbohydrates, fats, and proteins.[For more info., see: https://en.wikipedia.org/wiki/Mineral_(nutrient)]
For vitamin, I'll just give you the definition from the dictionary on my Apple computer: A vitamin is "any of a group of organic compounds which are essential for normal growth and nutrition and are required in small quantities in the diet because they cannot be synthesized by the body." Thus while fats, carbohydrates, and proteins are all organic compounds essential for life, they are not considered to be vitamins, because they are used in large quantities as either energy sources or building blocks.
So, in sum, in their dietary usage, a mineral is an essential element needed in small amounts, and a vitamin is an essential organic compound needed in small amounts.