The Periodic Table of Elements

The chemical elements are arranged in a chart called the Periodic Table of Elements. The table of elements represents the building blocks of everything—both living and nonliving. About 90 elements have been identified as occurring naturally on Earth. The Periodic Table of Elements is an important tool for scientists.

The table helps them understand the physical and chemical properties of individual elements.

Did you know?

Quantum mechanics is the study of matter and radiation at the atomic level.

Table 2.3 The Major Elements Found in the Human Body

Element

Symbol

Approximate Percent by Mass in Human Body

Oxygen

O

65,0

Carbon

C

18.5

Hydrogen

H

9.5

Nitrogen

N

3.3

Calcium

C

1.5

Phosphorus

P

1.0

Potassium

K

0.4

Sulfur

S

0.3

Sodium

Na

0.2

Chlorine

Cl

0.2

Magnesium

Mg

0.1

The Periodic Table can be divided into three basic groups ofelements. The groups include metals, nonmetals, and semimetals or metalloids. Semi-metals have the properties of both metals and nonmetals. Chemists use one or two letter symbols to represent elements. As an example, the symbol for aluminum is Al. The symbol for oxygen is O.

• The metal elements make up the majority of the groups of elements— more than 70 percent. Some of these metals include potassium, calcium, sodium, barium, and the more familiar ones include such metals as tin, lead, aluminum, copper, mercury, silver, and gold. Mercury is the only metallic element that is liquid at room temperature. Gold and silver nanoparticles are used in medical research and for treating burns and wounds and in cancer research. Most metals are good conductors of electricity and heat and are malleable—easy to bend and shape. However, electrical conductivity in metal decreases with increasing temperature, whereas in semiconductors, electrical conductivity increases with increasing temperature.

• Some of the nonmetals include chlorine, bromine, iodine, and fluorine. The nonmetals are dull in color, usually brittle, and are poor conductors of electricity and heat. You are not going to find too many of these elements in nanofabrication.

• A few elements are classified as metalloids or semimetals because they are between a metal and a nonmetal. The metalloids include silicon (S), boron (B), germanium (Ge), arsenic (As), and tin (Sn). Metalloids have properties of both metals and nonmetals.

Some of the metalloids, such as silicon and germanium, are used as semiconductors in transistors. Transistors are the fundamental building blocks of a microchip and are built on a silicon base.

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