Final answer:
Group 1 elements, which include hydrogen and the alkali metals, each have one valence electron. This single electron is significant in determining the reactivity of these elements and their tendency to form bonds, especially with halogens in group 17 to create ionic compounds.
Step-by-step explanation:
Elements in group 1 of the periodic table are known for having one valence electron. This characteristic is a part of a broader periodic trend where the elements in the same group share the same number of valence electrons. In group 1, which includes hydrogen and the alkali metals, each element has a single electron in its outermost shell. This plays a crucial role in defining the chemical properties of these elements, especially their reactivity and how they form bonds with other elements.
Understanding valence electrons is essential when predicting how atoms will interact during chemical reactions. For instance, the valence electrons are used to form chemical bonds, with group 1 elements typically losing their one valence electron to achieve a stable electronic configuration. This is why group 1 elements are very reactive and readily form ionic compounds with elements that have seven valence electrons, like the halogens in group 17.
The next group in the periodic table, group 2, contains alkaline earth metals each having two valence electrons. As one moves left to right across a period, there is a gradual increase in the number of valence electrons up through group 18, the noble gases, which have eight valence electrons, giving them special stability due to a full outer level of s and p sublevels.