Which electron arrangement characterizes elements in Group 1 of the periodic table?

Elements in Group 1 of the periodic table are characterized by having a single electron in their outermost shell. This is represented by the electron arrangement notation ns^1, where 'n' refers to the principal quantum number that indicates the energy level of the electrons, and 's' indicates that the electron is in an 's' orbital. Group 1 elements, commonly known as alkali metals, include lithium, sodium, potassium, and others, all of which share this unique outer electron configuration.

The presence of this single valence electron in the s orbital is significant because it makes these elements highly reactive, as they tend to lose that one electron easily in chemical reactions, forming positive ions with a charge of +1. This reactivity is a defining characteristic of the alkali metals, differentiating them from elements in other groups with different electron arrangements, such as the noble gases or halogens, which have different numbers of valence electrons.