Group 1 metals, commonly referred to as alkali metals, form +1 ions due to their unique electron configuration, characterized by a single electron in their outermost shell. This electron is readily lost, allowing the atom to attain a more stable electron arrangement.

The alkali metals include lithium ($\text{Li}$), sodium ($\text{Na}$), potassium ($\text{K}$), rubidium ($\text{Rb}$), cesium ($\text{Cs}$), and francium ($\text{Fr}$). These elements occupy the first column of the periodic table and exhibit similar chemical properties, one of which is their propensity to form +1 ions.

The electron configuration of an atom plays a crucial role in determining its chemical behavior. For group 1 metals, the presence of a single electron in their outermost shell, known as the valence shell, makes them particularly reactive. This valence electron is situated far from the nucleus and experiences a weaker attractive force from the positively charged protons, making it easier to remove.

When a group 1 metal atom loses its outermost electron, it transforms into a +1 ion. This occurs because the atom then possesses one more proton (a positively charged particle) than it does electrons (which carry a negative charge), resulting in an overall charge of +1. The removal of this electron allows the atom to achieve a stable electron configuration, similar to that of noble gases, which are known for their stability and lack of reactivity. Other elements often engage in reactions that lead to a comparable stable configuration.

This process of losing an electron is referred to as ionization. The first ionization energy is defined as the energy required to remove one electron from an atom. Group 1 metals exhibit relatively low first ionization energies, meaning that less energy is needed to remove their outermost electron compared to elements in other groups. This characteristic further explains why they readily form +1 ions.

In summary, the ability of group 1 metals to form +1 ions stems from their electron configuration and the principles of ionization. By losing their outermost electron, these metals not only achieve a stable electron configuration but also acquire an overall positive charge.