The Simplest Matter

The ElementsAn element is matter made of only one kind of atom. There are

110 known elements, and 90

of those occur naturally on

Earth.

Chemists have created a chart called the Periodic Table of the

Elements to help them organize and display the elements.

The Periodic TableThe elements are organized on the

periodic table by their properties. There are

rows and columns that represent

relationships between the elements.

The Periodic Table

The rows in the table are called periods. The elements in a row

have the same number of energy levels.

The Periodic Table

The columns are called groups. The elements in each group have

similar properties related to their structure.

Atomic NumberChemic

al Symbol

Atomic Mass

In the periodic table, each element is

represented by a chemical symbol that

contains one to three letters.

Chemical Symbol

Atomic Numbe

rThe atomic

number tells you the

number of protons in

the nucleus of that

element.

Atomic Mass

The atomic mass is the

average mass of an atom.

Classification of Elements

Elements fall into three general categories – metals, metalloids, and

nonmetals. The elements in each category have similar properties.

MetalsMetals generally have a shiny or

metallic luster and are good conductors of heat and electricity.

All metals except mercury, are solid at room temperature.

Nonmetals

Nonmetals are elements that are usually dull in appearance. Most are poor conductors of heat and electricity. Also, many are gases

at room temperature.

MetalloidsMetalloids are elements that

have characteristics of

metals and nonmetals. All metalloids are solids at room temperature.