Kristi Lew - The 15 Lanthanides and the 15 Actinides

Published in 2010 by The Rosen Publishing Group, Inc.
29 East 21st Street, New York, NY 10010

Copyright 2010 by The Rosen Publishing Group, Inc.

First Edition

All rights reserved. No part of this book may be reproduced in any form without permission in writing from the publisher, except by a reviewer.

Library of Congress Cataloging-in-Publication Data

Lew, Kristi.

The 15 lanthanides and the 15 actinides / Kristi Lew.1st ed.

p. cm.(Understanding the elements of the periodic table)

Includes bibliographical references and index.

ISBN 978-1-4358-3557-3 (library binding)

1. Rare earth metalsPopular works. 2. Actinide elementsPopular works. 3. Periodic lawPopular works. I. Title. II. Title: Fifteen lanthanides and the fifteen actinides.

QD172.R2L49 2010

546'.41dc22

2009014416

Manufactured in the United States of America

On the cover: The lanthanides and actinides squares on the periodic table of elements

Contents

Introduction

T he periodic table of elements is a chart that is used by chemists to organize all the known chemical elements. A chemical element is a substance that is made up of only one type of atom. Chemical elements are the building blocks of all matter. (Matter is anything that has weight and takes up space.) Gold (Au), silver (Ag), and oxygen (O), for example, are all chemical elements. An element cannot be broken down by ordinary physical or chemical means, such as heating it up or passing electricity through it.

One of the first periodic tables was developed in 1869 by a Russian chemist named Dmitry Mendeleyev (18341907). To design his periodic table, Mendeleyev arranged all the elements known at that time (about sixty of them) in order of increasing atomic weight. He discovered that the properties of the elements repeated at regular, or periodic, intervals. Therefore, Mendeleyev arranged the elements in rows, or periods. A new row was started whenever the properties of the elements began to repeat. This way, all the elements in the same column, or group, had similar physical properties. These physical properties could include color, hardness, and the temperatures at which they melt and boil. Elements in the same group also behave similarly in chemical reactions.

In 1869, Dmitry Mendeleyev placed all of the known chemical elements into groups with similar properties. This chart became known as the periodic table of the elements. Here is Mendeleyevs first periodic table, published in 1869.

While developing his periodic table, Mendeleyev sometimes came to a spot where none of the known elements exhibited the correct properties to fill in the space. When this happened, Mendeleyev left a gap in his chart. He predicted that, someday, scientists would discover elements that would fill in the blanks. He even predicted what properties these elements would have. Some scientists did not believe Mendeleyev, but he was proven correct when the elements gallium (Ga), scandium (Sc), and germanium (Ge) were discovered in 1875, 1879, and 1886, respectively. These elements all possessed the properties that Mendeleyev had predicted. Each fit neatly into blank spaces that he left in his periodic table.

The modern periodic table is no longer arranged by increasing atomic weight. Instead, the elements are ordered according to increasing atomic number. Uranium (U), for example, has an atomic number of 92. It can be found in one of the two rows of elements at the very bottom of the periodic table. These two blocks of elements are labeled the lanthanide series and the actinide series.

The first element in the lanthanide series is lanthanum (La). Lanthanum has an atomic number of 57 and can be found in period 6, group 3 (or IIIB in an older naming system). The lanthanides are sometimes called the rare earth elements. Uranium is an element in the actinide series. The actinide series begins with the element actinium (Ac) at atomic number 89 and continues through lawrencium (Lr), atomic number 103. There are fifteen lanthanide elements and fifteen actinide elements.

Some of the rare earth elements can be very useful in everyday life. Gadolinium (Gd), for example, is used to make compact discs, and terbium (Tb) is found in microprocessor chips used in computers. The actinides uranium and plutonium (Pu) are important, too. These elements are used as fuel sources in nuclear power plants that can produce electricity for cities and towns. Indeed, the lanthanides and actinides can be found in products ranging from movie projectors and color televisions to airplane parts and decorative glass bowls. Without these elements, everyday life would be very different.

Chapter One

What Are the Lanthanides and Actinides?

O f the thirty elements that make up the lanthanides and actinides, a little more than half of them are found naturally in Earths crust. The others are synthetic and are made in nuclear reactors or particle accelerators.

Naturally Occurring Elements

In 1787, an amateur geologist named Carl Axel Arrhenius (17571824) discovered a new mineral near the village of Ytterby, Sweden. He named this new mineral ytterbite. This black stone is made up of many of the lanthanides. This marked the first discovery of the lanthanide elements. And in 1989, the mine where Arrhenius found ytterbite was designated a historical monument.

Seven years after Arrhenius discovered ytterbite, a Finnish chemist named Johan Gadolin (17601852) began to study the mineral. Gadolin realized that ytterbite (known today as gadolinite) contained several unknown elements. While Gadolin was never able to isolate any of these elements, one of the lanthanides, gadolinium, would later be named for him to acknowledge his work.

It took nine more years before the first of the lanthanides, cerium (Ce), was identified. It was identified by Martin Heinrich Klaproth (17431817), a German chemist, as well as Jns Jacob Berzelius (17791848) and Wilhelm von Hisinger (17661852), both Swedish chemists. Even though these three scientists are credited for finding cerium, what they actually found was a chemical compound of cerium. A chemical compound is made up of two or more elements that are chemically bonded together. The compound they found was an oxide of cerium (meaning that it contained the element oxygen, as well as cerium). Scientists at that time did not have the technology they needed to isolate the element, but they did name it. The element was named cerium in honor of the first asteroid, Ceres, which had been discovered two years earlier in 1801.

The lanthanides include the fifteen elements from lanthanum to lutetium (Lu). All but one of the lanthanides occur naturally. Most of the actinides, however, are synthetic. They include the fifteen elements from actinium to lawrencium.

A Swedish chemist named Carl Gustaf Mosander (17971858) came to the conclusion that ceria contained at least two oxides. He kept the name ceria for one of them and named the other lanthana, from the Greek word meaning to lie hidden. It was later determined that lanthana was made up of lanthanum oxide. In 1841, Mosander separated yet another substance from ceria. He named it didymium, from the Greek word for twin, because he always found it in the same rocks with lanthana. In the next couple of years, Mosander went on to discover two other lanthanides, erbium (Er) in 1842 and terbium in 1843. The American chemists William Frances Hillebrand (18531925) and Thomas H. Norton would isolate cerium in 1875.