ACS Chemistry Practice Exam 2025 – The All-in-One Guide to Exam Success!

An alkali metal is characterized by having a single electron in its outermost shell, which is reflected in its electronic configuration as ns1. The 'n' represents the principal quantum number of the outermost shell, and the 's' subshell holds the single electron.

Alkali metals include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr), all found in Group 1 of the periodic table. They share similar chemical properties largely due to this singular outer electron, which is readily lost in chemical reactions, leading to the formation of cations with a +1 charge.

The other configurations mentioned pertain to different groups of elements. For example, ns2 represents alkaline earth metals that have two valence electrons, ns2np1 corresponds to Group 13 elements such as aluminum, and ns2np5 is associated with halogens that have seven valence electrons. Understanding these configurations can help in distinguishing and identifying the elements based on their group characteristics within the periodic table.