Final answer:
Valence electrons in main group elements are determined by their group number on the periodic table, with Group 1 having one valence electron and Group 18 having eight. These electrons determine the chemical properties and reactions of the element. Main group metals tend to lose electrons when forming cations, while nonmetals tend to gain electrons to form anions.
Step-by-step explanation:
Understanding Valence Electrons in Main Group Elements
The valence electrons for the main group elements can typically be identified by the group number on the periodic table. With the exception of the transition metals (groups 3-12), the valence electrons of an element can be determined as follows:
For Group 1 (alkali metals), atoms have one valence electron.
For Group 2 (alkaline earth metals), atoms have two valence electrons.
For Groups 13 to 18, the number of valence electrons is equal to the group number minus ten. For instance, Group 13 has three valence electrons, progressing up to Group 18, which has eight.
The main group elements, also known as representative elements, include those elements where the last electron added enters an s or a p orbital in the outermost shell. These are the electrons with the highest principal quantum number (n) and determine the chemical behavior of the element.
When main group elements form cations, they tend to lose their valence electrons to achieve the electron configuration of the nearest noble gas. For example, the alkaline earth metal calcium (Ca) has two valence electrons and forms a Ca2+ ion upon their removal, becoming isoelectronic with argon (Ar).
Conversely, main-group nonmetals tend to gain electrons to achieve a stable octet structure. For instance, oxygen (in Group 16) can accept two electrons to achieve the electron configuration of neon, resulting in the oxide ion (O2-).