A Level Chemistry OCR Practice Exam

What is referred to as a 'period' in the context of the Periodic Table?

1. A vertical column of elements

2. A horizontal row of elements

3. A group of elements sharing similar properties

4. A classification of elements based on reactivity

The correct answer is: A horizontal row of elements

In the context of the Periodic Table, a 'period' refers to a horizontal row of elements. Each period corresponds to the number of energy levels (shells) that the elements in that row possess. As you move from left to right across a period, the atomic number increases, and you can observe a gradual change in properties of the elements, such as from metals to non-metals. This arrangement is fundamental to understanding trends in atomic structure and elemental behavior, such as electronegativity, atomic radius, and ionization energy. The horizontal organization of elements allows for the identification of trends across periods that are not present when examining vertical columns. In contrast, vertical columns are referred to as groups or families, and they contain elements that often share similar chemical properties.