They share their valence electrons
Most atoms are stable when they have a full outer energy level, which typically consists of 8 electrons. This is known as the octet rule. However, some smaller atoms, such as hydrogen and helium, are stable with only 2 electrons in their outer energy level.
Atoms with a complete outer energy level or stable octet are more stable and less likely to react with other atoms. Inert gases like helium, neon, and argon have full outer energy levels and do not readily react with other elements, making them chemically stable.
The most stable atoms/ions have 8 electrons in their outermost shell.
Atoms want to have a full outer energy level of electrons, typically either 2 or 8 electrons, to become stable. This is known as the octet rule, in which atoms tend to gain, lose, or share electrons to achieve a stable electron configuration like the noble gases.
Most atoms require eight electrons in the outer shell to be stable. The exception is atoms that are only filling the s1 orbital, which becomes stable with only two electrons.
A completley filled out electron level makes the atom stable
Hydrogen is an atom that does not need 8 electrons in its outer energy level to be stable. Hydrogen only needs 2 electrons to fill its outer energy level.
Calcium atoms have two electrons in the s orbital of their outermost energy level. Their electron configuration is [Ar]4s2.
Energy levels
Stable.
If the outer energy level of an atom is already filled with electrons, it is less likely to react because atoms tend to be more stable when their outer energy levels are full. This full outer level signifies that the atom has achieved a more stable electron configuration (usually the octet rule for most elements).
All the noble gases Helium, Neon, Argon, Krypton, Xenon and Radon have a stable octet of electrons in their outer energy level.