When matter is squeezed, the electronic structure of the atoms can be significantly altered from their ground state configuration at ambient pressure (or in vacuo). With sufficient compression, core levels will become more accessible (i.e., closer to the valence), resulting in a less distinct core-valence separation. This has important implications for the chemistry of elements. Understanding the way matter responds to compression, both chemically and physically, is crucial for various interdisciplinary fields, including geology, planetary science and material science. Consequently, simple systems such as unary and binary compounds, are the focus of scientists aiming to establish general principles for the behavior of matter under high pressure. In alkali and alkaline earth metals, for example, it was shown that at 70 GPa, Cs-VI promotes the hybridization of the semi-core 5s and 5p orbitals with the 6s and 5d. Regarding s-block binary systems, it is predicted that at P ~ 100 GPa, hydrogen rich compounds of rubidium , cesium and calcium become stable where the semi-core electrons are engaged in chemical bonding. Shortly after, the activation of the 5p electrons of cesium was theorized at only 10 -20 GPa, by using an excess of strongly oxidizing elements like fluorine, forming species having stoichiometry CsFn, with n > 1. Furthermore, the involvement of semi-core electrons in chemical bonding has been predicted even in gas phase, like for the highly oxidized [CsO4] + cation. Hence, good triggers for the semi-core shells of s-block elements seems to be compression and excess of oxidating agents. One may argue that, in the case of alkali and alkaline earth metals, once they are oxidized to their standard +1 or +2 states, the lower p-orbitals, if present, are technically the new valence orbitals. However, this scenario also corresponds to a noble gas electronic configuration, in addition to a positive charge, which makes these p-orbitals very inert.