Element Idle

1. 
   First Contact

   Make your first click.
   98%
2. 
   Nuclear Fission

   Purchase the Nucleus and unlock the skill tree.
   97%
3. 
   Chain Reaction

   Accumulate 1,000,000 particles in a single run.
   68%
4. 
   Critical Mass

   Accumulate 10,000,000 particles in a single run.
   65%
5. 
   Supercritical

   Accumulate 100,000,000 particles in a single run.
   63%
6. 
   Meltdown

   Accumulate 1,000,000,000 particles in a single run.
   62%
7. 
   New Element

   Perform your first prestige.
   78%
8. 
   Splitting the Atom

   Purchase Chain Reaction on the Proton path.
   84%
9. 
   Tunneling Through

   Purchase Quantum Tunneling on the Neutron path.
   81%
10. 
    Wave-Particle

    Purchase Superposition on the Electron path.
    73%
11. 
    Half-Life

    Purchase any branch capstone node.
    63%
12. 
    Fully Charged

    Purchase all 51 skill tree nodes.
    39%
13. 
    Noble Gas

    Unlock Neon, the first noble gas.
    61%
14. 
    Mendeleev's Dream

    Unlock Tin, element #50.
    42%
15. 
    Oganesson

    Unlock all 118 elements on the periodic table.
    16%

Names, descriptions and icons are the game’s own, as Steam publishes them; the share is how many owners have unlocked each, from Steam's global figures for 15 of them.