Intro To Chem - Bio

Octet rule: atoms gain/lose/share electrons to achieve a full valence shell of 8 electrons; hydrogen follows a duet (2 electrons).
Bonding type: covalent bonds involve sharing electrons to satisfy the octet.
Electron configurations:
- Oxygen: $1s^2\ 2s^2\ 2p^4$ ; valence electrons = $6$ ; needs $2$ more to complete the octet.
- Hydrogen: $1s^1$ ; valence electrons = $1$ ; needs $1$ to reach the duet.
Water formation (example): $\mathrm{H_2O}$ forms via two covalent O–H bonds; oxygen shares electrons with each hydrogen; around O there are $8$ electrons; each H has $2$ electrons.

Structure: $\mathrm{H_2O}$ ; H–O–H.
Bond type: covalent single bonds.
Electron accounting: O contributes two electrons (one to each bond); each H contributes one electron; around O: $8$ electrons; around each H: $2$ electrons.

Oxygen’s outer shell is not already full: the second shell holds $6$ valence electrons and needs $2$ more to reach the octet.
Hydrogen requires a duet (2 electrons), not a full octet.
Octet rule applies broadly in main-group elements; hydrogen is an exception to the octet rule when considering larger contexts, but forms stable H–X bonds by achieving a duet.

Octet rule drives bonding; H needs $2$ electrons in total (duet); O needs $2$ more to reach octet.
H2O forms via two covalent bonds; structural formula H–O–H; electrons are shared to give O an octet and H a duet.