The fundamental nature of every atom and its capacity to interact with others is governed by valence electrons. These electrons are the outermost occupants of an atom’s electron cloud, and their arrangement dictates how an element will behave chemically and what compounds it can form. Determining this count is the first step for predicting an element’s reactivity and tendency to bond with other substances.
Defining Valence Electrons and the Count for Rubidium
A valence electron is an electron residing in the highest occupied energy level, or outermost shell, of an atom. These electrons are available to be shared or transferred during a chemical reaction. Rubidium (Rb), atomic number 37, is a soft, silvery-white metal.
The definitive answer is one valence electron. This single electron is located in the atom’s fifth occupied energy shell, specifically in the \(5s\) orbital, as shown by its electron configuration, \([\text{Kr}]5s^1\). This configuration means the atom has the stable electron arrangement of the noble gas Krypton, plus this one additional electron in the outermost shell.
Rubidium’s Position on the Periodic Table
Scientists can determine an atom’s valence electron count using its placement on the periodic table, rather than determining its full electron configuration. Rubidium is located in Group 1, the first vertical column. For main group elements, the group number precisely corresponds to the number of valence electrons.
This Group 1 location classifies Rubidium as an alkali metal, a family of elements defined by having one valence electron. Rubidium is located in Period 5, the fifth horizontal row. This period number indicates that a Rubidium atom has five distinct electron shells, with the outermost shell containing the single valence electron.
How One Valence Electron Influences Reactivity
The presence of a single valence electron influences Rubidium’s chemical identity, driven by the desire for a full outer electron shell. This stability is described by the octet rule, which states that atoms tend to react to achieve eight electrons in their outermost shell. For Rubidium, the fastest path to stability is to lose its lone valence electron, rather than gaining seven.
When Rubidium readily releases this electron, it achieves the stable, full-shell configuration of the noble gas Krypton, forming a positively charged ion, \(\text{Rb}^+\). This powerful urge to surrender the electron makes Rubidium one of the most reactive elements, characterized by a very low first ionization energy. This tendency to lose its electron means Rubidium reacts violently with substances like water, producing Rubidium hydroxide and igniting the hydrogen gas that is rapidly released.