Final answer:
Elements in a period on the periodic table are similar in terms of chemical properties due to their similar number and distribution of electrons in their valence shells.
Step-by-step explanation:
The elements in a period on the periodic table are similar in terms of chemical properties. This is because elements in the same period have the same number and distribution of electrons in their valence shells, which determines their chemical behavior. For example, all elements in a period have the same number of electron shells, which affects their reactivity. However, elements in a period may have different atomic numbers, physical states, and atomic masses.