Representative elements use which designation to determine their valence electrons?

• A. Period number
• B. Group numbers (1A-8A)
• C. Atomic mass
• D. Electron spin configuration

Answer: (B)

Valence electrons for representative (main-group) elements are read off from the element’s group on the periodic table. The group numbers, historically labeled as 1A–8A, tell you exactly how many valence electrons those elements have. For example, elements in the group with 1A have one valence electron, those in the group with 2A have two, and so on up to 8A with eight valence electrons. The period number would indicate the energy level of the outer shell, atomic mass is not a direct indicator of valence electrons, and electron spin configuration isn’t used to count valence electrons.