Unit 4: Up Close: The Periodic Table of Elements

Section 3: Metalloids

• Introduction
• Properties of Metalloids
• Some Metalloids

Introduction

In nature, there are elements that we can classfify as metals or nonmetals. Elements that are metals tend to give up electrons to form an ionic compound. Elements that are nonmetals tend to gain electrons in molecular compounds. Metals are metallic in apperance, whereas nonmetals are nonmetalllic. What about elements that fit in between these two distinct definitions for a metal and nonmetal? The classfication for these elements is a group called metalloids.

Properties of Metalloids

Metalloids exhibit properties simalar to metals and nonmetals. Elements in the metalloid group may form ionic or convalent bonds in compounds. Metalloids can conduct electricity poorly under certain conditons. They are called semiconductors. Semiconductors can be used in microcircuitry, electronics, and computers due to this property. A boundary for metals and nonmetals can be found towards the right hand of the perodic table. Along this boundary are the metalloids: boron, silicon, germanium, arsenic, antimony, tellurium, and polonium. Aluminum and astatine are not metalloids.

Some Metalloids

Boron

Boron is a metalloid even though it forms some compounds with unusal properties. For example, boron and boron carbide form crystals with a hardness similar to diamonds. These crystals can be used to cut, grind, and polish serveral materials.

Arsenic

Arsenic comes in two forms in the same physical states. Two or more different forms of a element in the same physical states are called allotropes. The two allotropes of arsenic are gray, metallic arsenic and yellow, nonmetallic arsenic (As4). These two forms of arsenic are of the same element but have different molecular structures. Arsenic is used as a poision to kill to weeds and insects.

Silicon

Silicon is the second most abundant element in the Earth's crust. It is the most common metalloid. When silicon forms a compound with oxygen, it is known as a silicate. Sand, clay, and most minerals that form rocks are composed of silicate. Silicates are also used to make glass.

Silicon dioxide, SiO₂, is present in the nimeral quartz, and is known as silica. Silicon can also be joined to a hydrocarbon to yield sythetic compounds known as silicones. Slicone is not present in nature. Silicone can be used to waterproof paper and fabrics and prevent corrosion in metals.