Periodicity

In this unit on Periodicity, we will examine the periodic table and understand how it was built. This will encompass knowing the various regions of the periodic table and, more importantly, understanding the organizational structure behind the table. 

Development of the Periodic Table

The Periodic Table was the culmination of more than a century of work to classify and organize elements by their properties. Although Dmitri Mendeleev is generally credited with the creation of the modern table, the history is more interesting and nuanced.

Periods and Families

Because the rows of the periodic table were created to show the repetitive (periodic) nature of many atomic properties, each row of the table is called a period.
The vertical columns are called groups or families.
That means that sulfur, S, is in the Oxygen family in the third period (in oxygen's column and on the third row of the table).

Regions of the Periodic Table

Many of the families on the periodic table, as well as some larger regions of the table, have special names. These are detailed in the diagram below.

Metals v. Non-metals and metalloids

To understand the difference between metals and non-metals, you need to know the properties of metals. Metalloids are simply those elements that show some, but not all, of the properties of a metal.

Periodic Properties

The periodic table gets it name from the fact that it is built on the periodic nature of a number of properties. In other words these properties demonstrate a cyclic nature, they rise and then fall, rise and then fall repeatedly and predictably. By understanding these properties we can begin to appreciate the remarkable document that is the periodic table.

We will be looking at five properties in this unit. They are ionization energy (also known as ionization potential), electron affinity, electronegativity, atomic radius and ionic radius. We will begin by looking at these five periodic properties. We will then look at the periodic table and the things we already know atomic number and electron configurations to understand why there are trends. Then, we will look at the trends themselves and understand how the structure of the atoms is related to each of the five properties and how changing atomic structure creates periodic patterns in those properties. You will also need to know about several exceptions to the trends that occur and why they occur.