﻿ ﻿Repeating Patterns: The Modern Periodic Table - The Periodic Table - Chemistry Essentials for Dummies

## Chemistry Essentials for Dummies

Chapter 3. The Periodic Table

In This Chapter

· Understanding periodicity

· Figuring out how elements are organized in the periodic table

Chemists like to put things together into groups based on similar properties. This process, called classification, makes studying a particular system much easier. Scientists grouped the elements in the periodic table so they don’t have to memorize the properties of individual elements. With the periodic table, they can just remember the properties of the various groups.

The periodic table is the most important tool a chemist possesses. So in this chapter, I show you how the elements are arranged in the table, and I show you some important groups. I also explain how chemists and other scientists use the periodic table.

Repeating Patterns: The Modern Periodic Table

In nature, as well as in things that humankind invents, you may notice some repeating patterns. The seasons repeat their pattern of fall, winter, spring, and summer. The tides repeat their pattern of rising and falling. Tuesday follows Monday, December follows November, and so on. A pattern of repeating order is called periodicity.

In the mid-1800s, Dmitri Mendeleev, a Russian chemist, noticed a repeating pattern of chemical properties in the elements that were known at the time. Mendeleev arranged the elements in order of increasing atomic mass (see Chapter 2 for a description of atomic mass) to form something that fairly closely resembles the modern periodic table. He was even able to predict the properties of some of the then-unknown elements. Later, the elements were rearranged in order of increasing atomic number, the number of protons in the nucleus of the atom. Figure 3-1 shows the modern periodic table.

PERIODIC TABLE OF THE ELEMENTS

§ Note: Elements 113, 115, and 117 are not known at this time, but are included in the table to show their expected positions.

Figure 3-1: The periodic table.

﻿