Question

why can a hydrogen atom form a covalent bond without fulfilling the octet rule?
○ hydrogens valence shell can hold only up to two electrons.
○ hydrogens valence shell never needs to be full to be stable.
○ the octet rule only applies to bonds formed by trading electrons.
○ the octet rule only applies to alkali metals and alkaline earth metals

Explanation:

Hydrogen has a valence shell that can hold only up to two electrons. The octet rule (which states that atoms tend to gain, lose, or share electrons to have eight electrons in their valence shell) is mainly for atoms with valence shells in the second energy level and beyond. Hydrogen's valence shell is the first energy level (\(1s\)) which can hold a maximum of 2 electrons. So, it can form a covalent bond (by sharing one electron) to achieve a stable electron configuration (2 electrons in its valence shell) without following the octet rule (which is about 8 - electron valence shell).

Answer:

Hydrogen's valence shell can hold only up to two electrons.