Vision (Definition) Vision is a feature of a person's brain that allows him to see. He must have normal eyes, optic nerves (that stretch from the eyes to the back of his brain), and visual cortex (the vision center in the brain), in order to see properly. An ophthalmologist is a doctor specializing in vision. ...Read more.
The halogens or halogen elements (/ËhÃ¦lÉdÊÉn, ËheÉª-, -loÊ-, -ËdÊÉn/) are a group in the periodic table consisting of five chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). The artificially created element 117 (ununseptium) may also be a halogen.
-Organic compounds are divided into two main classes: hydrocarbons and hydrocarbon derivatives. -Hydrocarbon derivatives are molecular compounds of carbon and at least one other element that is not hydrogen. -Organic halides are organic compounds in which one or more hydrogen atoms have been replaced by halogen atoms.