The potential energy of an electron decreases as it approaches the nucleus, however the Heisenberg Uncertainty Principle requires the total energy of the electron to increase as the volume of the space it occupies diminishes. As the electron gets closer to the nucleus, the nuclear charge confines the electron to such a tiny volume of space that its energy rises, allowing it to "float" slightly away from the nucleus without ever falling into it. Close to the nucleus, kinetic energy of an electron is large.

A quantum particle can be described by the plot of the mathematical function related to findingthe particle ina given location at any time. If the particle is confioned to a box, it turns out that the wave (the graphical plot of the function, which appears as a wave) does not fall to zero at the edge of the box in which the particle is confined.

Instead, the particle has a finite probability of being found outside the box. This is called the "tunnel effect" - as the particle has an ability top tunnel through thr box in which it was thought to have been confined.

So an electron is able to leak out of an atom if another low energy location can be found nearby.

Electrons are able to tunnel through the potential energy barrier sparating two nuclei, and become simultaneously close to the nuclei. Because the tunnel effect allows for electrons to do this, (recall that there is aprobability they will be located "otside the box"), strong bonds can develop between atoms because of this tunneling effect.

Please do not think that intelligence is measured by a few specific questions about these topics.