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.
Halogens are generally poisonous; each has a different level of toxicity. Halogens are poor conductors of heat and electricity. Halogens can exist in all three classical states of matter: solid, liquid, and gas. Key Terms. diatomic: Consisting of two atoms. acid: An electron pair acceptor; generally capable of donating hydrogen ions.