Different states of elements

[Birt]

HI All I am a little confused. How can an element exist in 2 different states. For example Selenium can be either a red powder(or crystals) or a metal. How is this possible? I have also heard that hydrogen theorectically could exist in a metallic form under certain (extreme) conditions.

[jake-the-peg]

Elements can occur in multiple forms or allotropes

Classic example is carbon.

It can occur as diamond or graphite amounst other forms.

It's to do with how the atoms bind to each other.

http://en.wikipedia.org/wiki/Allotropy

Metalic Hydrogen is not so much allopropy as the gas condensing under huge pressure to a solid or liquid metal