whats the difference between bipolar and dementia?

Bipolar is swings between extreme manic(excited) and depressive states, usually over a period of days or weeks but for some extreme bipolar peoples it is hours or even minutes. This is a neurological condition that seems to have a strong genetic link.

Dementia is a series of cognitive failures due to neurological degeneracy of some kind, leading to thought processes that don't seem to make any sense to outsiders. Can be caused by age, malnutrition, disease or some form of poisoning/drug.

Dementia is a gradual deterioration of cognitive functions, most often found in the elderly. A bipolar disorder usually manifests far earlier, with the hallmarks of mood swings from depression to mania.

Mood swings caused by chemical imbalances vs Brain damage.