Bielementium Trophy in Mercury Hg

The level selection screen is the Periodic Table of the Elements. The Periodic Table is broken up into groups (that vary from the actual groups that the elements are in, but for the purposes of this game, it works). You will need different numbers of atoms to access each group. For the second group, you will need 25 atoms. The atoms are earned by completing levels and achieving the targets for each level. If you miss one of the targets/atoms in any level, you can go back and complete it again just to earn that one target. Every level has a maximum of four targets, so at the minimum, you will need to complete at least seven levels to open up the second group.

Note: The DLC levels do help to contribute towards your total needed to unlock the base groups.