Visit this website to view the periodic table. In the periodic table of the elements, elements in a single column have the same number of electrons that can participate in a chemical reaction. These electrons are known as “valence electrons.” For example, the elements in the first column all have a single valence electron, an electron that can be “donated” in a chemical reaction with another atom. What is the meaning of a mass number shown in parentheses?
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“The Periodic Table of the Elements ,” Open Educational Resource (OER) , accessed October 25, 2020, http://oer.iain-padangsidimpuan.ac.id/items/show/933.