International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

What do elements in the same group of the Periodic Table have in common?

1. The same atomic mass

2. The same number of neutrons

3. The same number of electrons in the outer shell

4. The same physical properties

The correct answer is: The same number of electrons in the outer shell

Elements in the same group of the Periodic Table share the characteristic of having the same number of electrons in their outer shell. This commonality is significant because the chemical properties of elements are largely determined by their valence (outer shell) electrons. For example, elements in Group 1, such as lithium, sodium, and potassium, all have one electron in their outer shell, which leads them to exhibit similar behaviors, such as reactivity with water. This similarity helps to explain why elements in the same group tend to form similar types of compounds and have comparable chemical reactivities. The outer shell electron configuration influences how an element interacts with other elements, including its tendency to lose, gain, or share electrons during chemical reactions. Elements do not necessarily have the same atomic mass or the same number of neutrons; those can vary significantly within a group. Additionally, while elements in the same group may have some similar physical properties as a result of their electron configuration, this is not a definitive characteristic, as physical properties can be influenced by other factors such as atomic size and weight. Thus, the correct answer emphasizes the importance of valence electrons in determining the chemical behavior of elements within the same group.