Answer:
In the periodic table, a group (also known as a family) is a vertical column of elements that share common characteristics. The elements in each group have similar chemical properties because they have the same number of valence electrons (the electrons in the outermost energy level of an atom). The number of valence electrons determines the element's reactivity and its ability to form chemical bonds. There are 18 main groups in the periodic table, and they are numbered from 1 to 18. The elements in Group 1 are known as the alkali metals, while the elements in Group 2 are known as the alkaline earth metals. The elements in Groups 3 through 12 are known as the transition metals, while the elements in Groups 13 through 18 are known as the post-transition metals. The elements in each group are listed in order of increasing atomic number.