Answer: A. need the same number of electrons to fill their valence shells
B. have the same number of valence electrons
Explanation:
Elements are distributed in groups and periods in a periodic table.
Elements that belong to same groups will show similar chemical properties because they have same number of valence electrons.
Example: Flourine, chlorine and bromine are elements which belong to Group 17. They have 9, 17 and 35 electrons respectively and contain 7 valence electrons each and need one electron to complete their octet.
The chemical reactivity of elements is governed by the valence electrons present in the element.
[tex]F:9:1s^22s^22p^5[/tex]
[tex]Cl:17:1s^22s^22p^63s^23p^5[/tex]
[tex]Br:35:1s^22s^22p^63s^23p^63d^{10}4s^24p^5[/tex]
