Final answer:
Metals have 1-3 valence electrons and usually lose electrons, while nonmetals have 4-7 and gain or share electrons to achieve a full shell similar to noble gases, which have eight valence electrons (except helium with two) and are highly stable.
Step-by-step explanation:
When looking at the number of valence electrons for metals, nonmetals, and noble gases on the periodic table, we can notice distinct patterns. Metals, typically found on the left side of the periodic table, have fewer valence electrons (1-3) and tend to lose these electrons to form cations, thereby achieving stability similar to the nearest noble gas. Nonmetals, found on the right side of the table (except for noble gases), generally have more valence electrons (4-7) and tend to either gain electrons to form anions or share electrons to create covalent bonds, which also reach a stable electronic configuration resembling that of a noble gas.
Noble gases, located in the far right column of the periodic table, possess a full valence shell; they have eight valence electrons (except helium, which has two) and are highly stable or inert due to this full valence shell, thus they rarely partake in chemical bonding. The noble gases show us that a fully occupied valence shell lends atoms maximum stability, which is why other elements undergo reactions to mimic this stability, primarily by gaining, losing, or sharing electrons to complete their outermost shell.