Answer:Elements in the same group on the periodic table have similar chemical and physical properties. This is because elements in the same group have the same number of valence electrons (electrons in the outermost shell of an atom), which determines how they will react chemically with other elements.For example, the elements in Group 1 of the periodic table (also known as the alkali metals) all have one valence electron. This means that they are highly reactive with other elements, particularly nonmetals, and tend to form ionic compounds with a +1 charge. They also have low melting and boiling points, and are soft and easily cut with a knife.Similarly, the elements in Group 17 (also known as the halogens) all have seven valence electrons, which makes them highly reactive with alkali metals and other elements. They tend to form ionic compounds with a -1 charge, and have high melting and boiling points.Therefore, elements in the same group on the periodic table have similar chemical and physical properties because they have the same number of valence electrons, which determines their reactivity and chemical behavior.