Final answer:
Valence electrons are the outermost electrons of an atom and are crucial for chemical reactivity. Main-group elements have a specific number of valence electrons that correlate with their group number. For example, Group 1 has one, while Group 18 has eight valence electrons.
Step-by-step explanation:
Valence electrons are the electrons in the outermost shell (or highest energy level) of an atom and are responsible for the chemical properties of the atom. They play a key role in the formation of chemical bonds. Looking at the main-group elements of the periodic table, the number of valence electrons corresponds to the group number for Groups 1-2 and 13-18. Specifically:
- Group 1 elements (alkali metals) have one valence electron.
- Group 2 elements (alkaline earth metals) have two valence electrons.
- Groups 13-18 elements have valence electrons equal to their group number minus ten (for example, Group 13 has three, while Group 18 has eight).
The valence electrons significantly affect the reactivity and bonding behavior of an element. Elements with a full valence shell, like the noble gases, are particularly stable and less chemically reactive.