Final answer:
Non-metals can achieve a full octet by forming covalent bonds with other non-metals or by gaining electrons to become anions. For example, group 15 elements form three covalent bonds, while halogens like chlorine gain one electron to form an anion.
Step-by-step explanation:
If non-metals need 8 valence electrons and they cannot interact with metals, they can achieve a full octet by sharing electrons with other non-metals through covalent bonds. Atoms form enough covalent bonds to supplement the electrons already present to possess an octet. For instance, members of group 15 in the periodic table, like nitrogen, have five valence electrons and can form three covalent bonds, as seen in the N₂ molecule, to complete their octet.
Other non-metals, such as those in group 17 known as halogens, need only one additional electron to achieve a noble gas configuration. Taking the example of chlorine, it has seven valence electrons and will readily accept one more to form a chloride ion (Cl⁻), thus reaching the desired octet and becoming an anion with a negative charge due to having more electrons than protons.
The octet rule is fundamental in predicting the structural behavior of non-metals and their ability to form compounds. However, it is important to note that there are exceptions, such as with hydrogen, and the transition and inner transition elements do not strictly follow the octet rule.