Here's why:
* Helium (He): Has 2 electrons in its outermost shell (1s²). This completely fills the first electron shell, making it very stable.
* Neon (Ne): Has 8 electrons in its outermost shell (2s² 2p⁶). This completely fills the second electron shell, making it highly stable.
* Xenon (Xe): Has 8 electrons in its outermost shell (5s² 5p⁶). While it has other shells, the outermost one is full, making it relatively stable.
Why stable electron configurations matter:
Atoms with stable electron configurations are less likely to participate in chemical reactions. This is because they already have a balanced and complete outer shell, so they don't need to gain or lose electrons to achieve stability.
These elements are known as noble gases due to their unreactive nature.
