Final answer:
Elements in the same group on the periodic table have the same number of valence electrons, such as alkali metals with one, alkaline earth metals with two, and halogens with seven, leading to similar chemical properties.
Step-by-step explanation:
Elements in the same chemical family or group on the periodic table have the same number of valence electrons, which play a crucial role in chemical reactions through the loss, gain, or sharing of these electrons. For example, the alkali metals lithium (Li) and sodium (Na) each have one valence electron. Likewise, the alkaline earth metals beryllium (Be) and magnesium (Mg) each have two valence electrons. The elements known as halogens, such as fluorine (F) and chlorine (Cl), each possess seven valence electrons. This consistent number of valence electrons within a group leads to similar chemical properties among the elements. When learning about chemical reactions and bonding, understanding the periodic trend of valence electrons is essential as it provides insight into how elements are likely to react.