(a) State the octet rule. (b) Does the octet rule apply to ionic as well as to covalent compounds? Explain using examples as appropriate.

(a) The octet rule states that atoms tend to combine in such a way that they each have eight electrons in their outermost electron shell, resulting in a more stable electron configuration. (b) Yes, the octet rule generally applies to both ionic and covalent compounds, though there are some exceptions. In ionic compounds, such as sodium chloride (NaCl), metal atoms transfer electrons to non-metal atoms, forming cations and anions that have complete octets. In covalent compounds, like water (H2O), atoms share electrons to achieve stable electron configurations with eight valence electrons (octet rule) or two valence electrons (duet rule, as in the case of hydrogen). However, elements in the third period and beyond may exceed the octet due to the presence of d-orbitals, and some elements like hydrogen follow the duet rule.