Associate Safety Professional Practice Exam

What is the term for the horizontal grouping of elements in the periodic table?

1. Family

2. Period

3. Group

4. Series

The correct answer is: Period

The term for the horizontal grouping of elements in the periodic table is known as a "period." Each period represents a new row in the table, where elements are arranged in order of increasing atomic number. This arrangement corresponds to the number of electron shells an atom has; for instance, elements in the first period have one electron shell, while those in the second period have two electron shells. Understanding the concept of periods is essential as it helps in recognizing the periodic trends, such as atomic size and ionization energy, that occur across a row. Elements in the same period, despite having different properties, show a gradual change in these properties as one moves from left to right across the table. In contrast, the other terms refer to vertical groupings and family classifications of elements rather than horizontal ones. For example, a "family" or "group" refers to the columns of the periodic table where elements share similar properties due to having the same number of electrons in their outermost shell. "Series" does not specifically apply to any consistent arrangement in the periodic table.