The Simplest Matter

The Elements An 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 Table The 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 Number Chemical Symbol Atomic Mass

In the periodic table, each element is represented by a chemical symbol that contains one to three letters. Chemical Symbol

Atomic Number The atomic number tells you the number of protons in the nucleus of that element.

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.

Metals Metals 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.

Metalloids Metalloids are elements that have characteristics of metals and nonmetals. All metalloids are solids at room temperature.