There's More to Chemistry than Outer Electrons

In my mental picture of chemical reactions, I consider outer electrons participate in activities, with a much lower probability of inner electrons getting in on the action. Could those electrons get involved in a reaction? Possibly, but in the general scheme of things it would be an extremely infrequent event. An article at ScienceNews describes computer simulations that indicate core electrons of highly pressurized atoms may interact significantly. Researchers at Dalhousie University calculated the behavior of lithium at pressures in excess of 1.5 million atmospheres and temperatures as high as 3,000 K. As the pressure was increased, the lithium atoms began to arrange themselves into unstable pyramids and the orbits of the core electrons began to change shape. Under normal temperatures and pressure, outer electrons are responsible for structure and reactivity. The simulations indicate the situation may be very different under extreme conditions, totally changing chemistry from what would usually occur.