[foorium]

The orbital structure is based off of tetrahedral with 1 lone pair therefore it should be 107o but Wikipedia says its 91.7? why is this?

[Schrödinger]

As you go down the group towards heavier elements, you find that the p-orbitals start participating in the bonding rather than the atomic orbitals getting hybridized.

I don't exactly know what it's called, but I remember having read this under 'Drago's rule' somewhere. But I'm not really sure. Someone please verify this.