An atom that has an outer shell that is not full is (more likely or less likely) to be reactive than an atom that has a full outer shell.

A half filled orbital is LESS LIKELY to be reactive than a fully filled orbital

Explanation: A fully filled orbital has the electronic configuration of a noble gas. That is, unreactive.

The quantum states of these orbitals(fully filled) are stable because the electrons in the sub shell are fully filled which makes it difficult for it to loose and gain electron unlike a half filled which is much more easier. It will take more energy for ionization to take place making it(fully filled) more stable.

meteorologists would compare a new weather map with one 24 h old to see how fast a front is moving.