As of Update 1.1.8, two new gameplay modifiers have been added: Gravitic Acceleration, and Electrostatic Acceleration! These modifiers are only available for local multiplayer and standard singleplayer modes. More details below:

Gravitic Acceleration:

• Applies a constant acceleration on all electrons towards the nucleus (or away from the nucleus, if you really want anti-grav.)
  
• Scales linearly with the atom (aka, the Magnesium nucleus has 12 times the gravity of Hydrogen's)
  

Electrostatic Acceleration:

• Applies an exponential acceleration on all electrons towards the nucleus and on all electrons away from each other (again, this is reversible)
  
• Scales linearly with the atom (aka, the Magnesium nucleus has 12 times the electric charge of Hydrogen's)
  
• Using the Neutron border (unlocked via the True Neutron achievement) grants immunity to this acceleration.
  

Note that BOTH may be active at the same time if so desired...
Enjoy!