The element represented by 'Hg' on the periodic table is mercury. It is a heavy, silvery-white metal that is unique for being a liquid at room temperature. Mercury has a variety of applications, including in thermometers, barometers, and some electrical switches. However, its use has significantly decreased due to health concerns, as mercury is toxic and can lead to severe environmental and health issues when not handled properly. In history, mercury has also been used in traditional medicine and alchemy. Despite its hazardous nature, mercury remains an interesting and complex element in the study of chemistry.