A Level Chemistry OCR Practice Exam

What is a 'group' in the context of the Periodic Table?

1. A horizontal row of elements with similar atomic mass.

2. A vertical column where elements have the same number of outer shell electrons.

3. A collection of elements that exhibit metallic properties.

4. A series of elements with identical electron configurations.

The correct answer is: A vertical column where elements have the same number of outer shell electrons.

In the context of the Periodic Table, a 'group' refers to a vertical column of elements that share similar chemical properties due to having the same number of outer shell electrons, also known as valence electrons. This characteristic is crucial because the number of valence electrons determines how an element reacts chemically and which compounds it can form. For example, elements in Group 1 all have one valence electron, making them highly reactive alkali metals. Similarly, the elements in Group 17, the halogens, have seven valence electrons, leading to their tendency to gain one electron during reactions to achieve a full outer shell. This shared characteristic within a group is what leads to similarities in physical and chemical behavior among the elements. The other options describe features that do not accurately define a group. While a horizontal row of elements with similar atomic mass refers to a period, a collection of elements that exhibit metallic properties does not encompass all elements in a group, and a series of elements with identical electron configurations is too broad and not a characteristic of a group in the Periodic Table. Thus, understanding that groups are defined by the number of outer shell electrons helps clarify their role and significance in chemical behavior.