Periodic Table of the Elements

Element Chemical & Physical Properties

More Periodic Table Information

• Periodic Table Study Guide
• Mendeleev's Original Periodic Table
• Element Photo Gallery
• Alphabetical List of Elements
• Atomic Numbers of the Elements
• Element Symbol Quiz
• Element Names Spelling Quiz
• Periodic Table Quiz
• Timeline of Element Discovery
• Trends (Periodicity) in the Periodic Table
• Introduction to the Periodic Table
• Element Groups
• Lanthanides & Actinides - The Rare Earths
• What Are the Elements in the Human Body?
• What Is the Most Abundant Element?

Introduction to the Periodic Table

People have known about elements like carbon and gold since ancient time. The elements couldn't be changed using any chemical method. Each element has a unique number of protons. If you examine samples of iron and silver, you can't tell how many protons the atoms have. However, you can tell the elements apart because they have different properties. You might notice there are more similarities between iron and silver than   between iron and oxygen. Could there be a way to organize the elements so you could tell at a glance which ones had similar properties?

What is the Periodic Table?

Dmitri Mendeleev was the first scientist to create a periodic table of the elements similar to the one we use today. You can see Mendeleev's original table (1869). This table showed that when the elements were ordered by increasing atomic weight, a pattern appeared where properties of the elements repeated periodically. This periodic table is a chart that groups the elements according to their similar properties.

Why was the Periodic Table Created?

Many elements remained to be discovered in Mendeleev's time. The periodic table helped predict the properties of new elements.

Mendeleev's Periodic Table

Compare the modern periodic table with Mendeleev's table. Mendeleev's table didn't have many elements. He had question marks and spaces between elements where he predicted   undiscovered elements would fit.

Discovering Elements

The number of protons determines the atomic number of an element, which its number on the periodic table. There aren't any skipped atomic  numbers on the modern periodic table because new elements are synthesized rather than discovered. The placement of these new elements on the periodic table can be used to help predict the element's properties.

Element Properties and Trends

The periodic table helps predict some properties of the elements   compared to each other. Atom size decreases as you move from left to   right across the table and increases as you move down a column. Energy   required to remove an electron from an atom increases as you move from   left to right and decreases as you move down a column. The ability to   form a chemical bond increases as you move from left to right and decreases as you move down a column.

Today's Periodic Table

The most important difference between Mendeleev's table and today's table is the modern table is organized by increasing atomic number, not increasing atomic weight. Why was the table changed? In 1914, Henry Moseley learned you could experimentally determine the atomic numbers of elements. Before that, atomic numbers were just the order of elements based on increasing atomic weight. Once atomic numbers had significance, the periodic table was reorganized.

Periods and Groups

Elements in the periodic table are arranged in periods (rows) and groups (columns). Atomic number increases as you move across a row or period.

Periods

Rows of elements are called periods. The period number of an element signifies the highest unexcited energy level for an electron in that element. The number of elements in a period increases as you move down the periodic table because there are more sublevels per level as the energy level of the atom increases.

Groups

Columns of elements help define element groups. Elements within a group share several common properties. Groups are elements have the same outer electron arrangement. The outer electrons are called valence electrons. Because they have the same number of valence electrons, elements in a group share similar chemical properties. The Roman numerals listed above each group are the usual number of valence electrons. For example, a group VA element will have 5 valence electrons.

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