In the periodic table, elements in the same group, also known as a column or family, typically have the same number of valence electrons. Valence electrons are the electrons in the outermost energy level of an atom and are involved in the chemical reactions and bonding behavior of elements.
The number of valence electrons determines many of the properties and chemical behavior of an element. Elements in the same group tend to have similar chemical properties because they have the same number of valence electrons, which results in similar electron configurations.
For example, elements in Group 1, also known as the alkali metals (e.g., lithium, sodium, potassium), all have one valence electron. Elements in Group 2, known as the alkaline earth metals (e.g., beryllium, magnesium, calcium), have two valence electrons. Elements in Group 17, the halogens (e.g., fluorine, chlorine, bromine), have seven valence electrons, and elements in Group 18, the noble gases (e.g., helium, neon, argon), have eight valence electrons (except helium, which has two).
Therefore, elements in the same group typically have the same number of valence electrons, which is a fundamental factor in determining their chemical behavior.