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.
Alkanes can react with halogens in the presence of UV light. During this reaction, halogen atoms substitute for (replace) hydrogen atoms, one at a time, producing a haloalkane and a hydrogen halide. Further substitutions are possible.Alkenes readily react with halogens under standard laboratory conditions.lkanes can react with halogens in the presence of UV light. During this reaction, halogen atoms substitute for (replace) hydrogen atoms, one at a time, producing a haloalkane and a hydrogen halide. Further substitutions are possible. Alkenes readily react with halogens under standard laboratory conditions.