# 9.1: The Periodic Table

Difficulty Level: At Grade Created by: CK-12

## Lesson Objectives

The student will:

• explain the periodic law.
• describe the differences among metals, nonmetals, and metalloids.
• draw a rough sketch of the modern periodic table and indicate the portion of the table occupied by metals, nonmetals, and metalloids.
• identify the stair-step line that separates the metallic elements from the nonmetallic ones.

• ductile
• malleable
• periodic law

## Introduction

In the periodic table, the elements are arranged according to similarities in their properties. The elements are listed in order of increasing atomic number as you read from left to right across a period. In this chapter, you will learn the general behavior and trends within the periodic table that result from this arrangement in order to predict the properties of the elements.

## The Periodic Law

The periodic table is a powerful tool that provides a way for chemists to organize the chemical elements. The word “periodic” means happening or recurring at regular intervals. The periodic law states that the properties of the elements recur periodically as their atomic numbers increase. This is because the electron configurations of the atoms vary periodically with their atomic number. Since the physical and chemical properties of elements depend on their electron configurations, many of the physical and chemical properties of the elements also tend to repeat in a pattern.

You may recall that the periodic table was created by Russian scientist Dmitri Mendeleev. Mendeleev used similarities in properties to construct his periodic table of the elements. He was even able to predict the properties of several elements missing from the periodic table by using the properties of neighboring elements. Mendeleev arranged the elements in a table by increasing atomic weight, although he sometimes had to ignore the atomic weights in order to group elements with similar chemical behaviors together.

The work of Henry Moseley led to the arrangement of elements based on their properties and atomic numbers, not atomic masses, which cleared up the inconsistencies of Mendeleev’s arrangement. Moseley’s periodic table is now considered the current periodic table.

## Metals, Nonmetals, and Metalloids

There is a progression from metals to nonmetals across each period of elements in the periodic table. The diagonal line at the right side of the table shown below separates the elements into two groups: the metals and the nonmetals. The elements that are on the left of this line tend to be metals, while those to the right tend to be nonmetals. The elements that are directly on the diagonal line are metalloids. Metallic character generally increases from top to bottom down a group and right to left across a period. The noticeable exception is hydrogen, which is grouped with the metals but is actually a nonmetal.

Most of the chemical elements are metals. Most metals have the common properties of being shiny, being very dense, and having high melting points. Metals tend to be ductile (can be drawn out into thin wires) and malleable (can be hammered into thin sheets). Metals are good conductors of heat and electricity. All metals are solids at room temperature except for mercury. In chemical reactions, metals easily lose electrons to form positive ions. Examples of metals are silver, gold, and zinc.

Nonmetals are generally brittle, dull, and have low melting points. They are generally poor conductors of heat and electricity. In chemical reactions, they tend to gain electrons to form negative ions. Examples of nonmetals are hydrogen, carbon, and nitrogen.

Metalloids have properties of both metals and nonmetals. Metalloids can be shiny or dull. Electricity and heat can travel through metalloids, although not as easily as they can through metals. They are also called semi-metals. They are typically semiconductors, which means that they conduct electricity better than insulators, but not as well as conductors. Semiconductors are valuable in the computer chip industry. Examples of metalloids are silicon and boron.

## Lesson Summary

• The word “periodic” means happening or recurring at regular intervals.
• The periodic law states that the properties of the elements recur periodically as their atomic numbers increase.
• There is a progression from metals to nonmetals across each period of elements in the periodic table.
• Metallic character generally increases from top to bottom down a group and right to left across a period.

This video is on the periodic table.

## Review Questions

1. Why is the table of elements called “the periodic table”?
1. It describes the periodic motion of celestial bodies.
2. It describes the periodic recurrence of chemical properties.
3. Because the rows are called periods.
4. Because the elements are grouped as metals, metalloids, and nonmetals.
5. None of these.
2. Which of the following elements is a nonmetal?
1. oxygen
3. iron
4. zinc
5. All of these are metals.
3. Which of the following metals is not an element?
1. gold
2. silver
3. copper
4. bronze
5. All of these are elements.
4. Which of the following elements is a metalloid?
1. chlorine
2. magnesium
3. rhenium
4. boron
5. None of these.

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