Lesson 5.2: Elements make up the periodic table

Lesson Focus

Discover how the periodic table brings order to all known elements. We'll explore how it systematically arranges them based on their properties, revealing predictable patterns and relationships that form the foundation of chemistry.

Learning Objectives

• Learn how the modern periodic table is organized by atomic number into specific groups and periods.
• Understand how an element’s position on the table reveals its key properties and predictable trends.

Seeing a repeating pattern in element properties, Dmitri Mendeleev arranged them by increasing atomic mass. He created the first periodic table, leaving gaps for elements he predicted would be discovered. This showed that organizing elements by their properties could reveal a hidden, predictable order in nature.

The modern periodic table is organized by an element's atomic number, which is its number of protons. This is a more precise method than using atomic mass. Each square gives key data: atomic number, symbol, name, and average mass. What fundamental property defines an element’s identity?

Vertical columns on the table are called groups. Elements within the same group, or family, have similar chemical properties because of their structure. For example, the elements in Group 1 are all highly reactive metals. Knowing an element's group helps you predict how it will behave chemically.

A horizontal row on the periodic table is called a period. As you move from left to right across a period, the properties of elements change in a predictable way. For example, elements transition from being highly metallic to nonmetallic, a pattern that repeats in every row.

An element's position reveals its tendency to form ions. Metals on the left, like in Group 1, lose electrons to form positive ions (1+). Nonmetals on the right, like in Group 17, gain electrons to form negative ions (1−). This helps predict how elements will react.