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Introduction to the Periodic Table of the Elements

Periodic Table with molecular model

Periodic Table with molecular model (OntheRunPhoto, iStockphoto)

Periodic Table with molecular model

Periodic Table with molecular model (OntheRunPhoto, iStockphoto)

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Learn about the elements of the periodic table and how they are organized.

Elements

Matter that is composed of only one type of atom is called an element. People have known about some elements such as gold, silver, iron, mercury and tin for hundreds of years. Scientists discovered many others during the 18th and 19th centuries. Some elements have even been discovered within your lifetime!

Naming the Elements

Many of the elements have their name or their symbol based in Latin or Greek. For example:

Element Atomic Symbol Word origin
Gold Au Latin word aurum meaning ‘shining dawn’
Mercury Hg Greek word hydrargyrum meaning ‘silver water’
Chlorine Cl Greek word chloros meaning ‘green’
Neon Ne Greek word neos meaning ‘new’ or ‘different’

As well for famous scientists such as:

Element Atomic Symbol Word origin
Curium Cm Pierre and Marie Curie (research in radioactivity)
Einsteinium Es Albert Einstein
Nobelium No Alfred Nobel (of Nobel Prize fame)
Mendelevium Md Dmitri Mendeleev (creator of the first periodic table)

Other elements have been named for places, such as:

Element Atomic Symbol Word origin
Europium Eu Europe
Francium Fr France
Germanium Ge Germany
Berkelium Bk Berkeley, California, USA
Dubnium Db Dubna, Russia

Did you know?

Argentina got its name from an element. Its name is from the latin name of silver, argentum. This is because its natives gave silver gifts to the first European conquerors.

The periodic table of the elements 

The periodic table of the elements is a visual and logical way to organize all elements. Dmitri Mendeleev, a Russian scientist, is usually credited with creating the first periodic table in 1869. In Germany, Lothar Meyer also came up with an almost identical table later the same year. Some people attribute the first categorization to Alexandre-Emile Béguyer de Chancourtois.

The periodic table of elements
The periodic table of elements (Source: Let’s Talk Science using an image by Dmarcus100 [CC-BY-SA] via Wikimedia Commons).

Each element on the periodic table is listed in a box with its atomic symbol and atomic number. The element’s full name and atomic mass is also sometimes indicated. The image below shows a typical entry for the element calcium.

Close-up of how an element is presented in the periodic table
Close-up of how an element is presented in the periodic table (©2021 Let’s Talk Science).

 The number above the atomic symbol represents the atomic number. The atomic number is equal to the number of protons in an atom's nucleus and determines which element an atom is. For example, any atom that contains exactly 20 protons in its nucleus is an atom of calcium. The number of protons influences the chemical behaviour of an element.

The atomic mass of an element refers to the average mass of an element in unified atomic mass units (short form u). This is usually given at the bottom of an element’s entry in the periodic table. The atomic mass is a decimal number because it is an average of the masses of the various isotopes of an element. Isotopes of an element have the same number of protons, but different numbers of neutrons. For example, hydrogen has three naturally occurring isotopes. The most common isotope, protium, has no neutrons! Deuterium has one neutron and tritium has two neutrons.

The three naturally-occurring isotopes of the hydrogen atom
The three naturally-occurring isotopes of the hydrogen atom (©2021 Let’s Talk Science).

Scientists have also created other highly unstable isotopes of hydrogen. Those, with up to 7 neutrons, do not occur in nature.

Getting the average number of neutrons for an element is easy. You need to subtract the number of protons (atomic number) from the atomic mass. For example, calcium has an atomic number of 20 and an atomic mass of 40.078 u. By subtracting 20 from 40 (rounded), we determine that the average number of neutrons is 20.

Arrangement of Elements 

Mendeleev organized the table so that the elements from low to high atomic mass. Then he organized rows and columns to highlight elements with similar chemical properties. The rows are known as periods. All elements in the same period have the same number of electron layers, also called shells. The columns are known as groups (or families).

Mendeleev also left gaps in his table. He believed that some elements had not yet been discovered. Those gaps were for undiscovered elements. Mendeleev predicted the missing elements would have the same properties as the other elements in the same column.

Discoveries led to many new elements during the 1900s. Mendeleïev’s table was rearranged to give us the format that we use today. But the principles of groups and periods still exist in our modern version.

The groups on the periodic table are numbered from 1 to 18. The elements within a group usually have similar properties. For example, the elements of group 18 are all gases that do not readily react with other elements. Groups can sometimes be given names. For example, the elements in group 18 are called ‘Noble Gases’.

Did you know?

Noble gases get their name because the ability to stay calm and not react is considered noble in humans!

The group of noble gases from the periodic table of elements
The group of noble gases from the periodic table of elements (Source: Let’s Talk Science using an image by Dmarcus100 [CC-BY-SA] via Wikimedia Commons).

Except for hydrogen, elements on the left side of the periodic table are metals. Metals are solid at room temperature, except for mercury, which is liquid. They are also malleable and can be ductile. Ductile is another word for stretchy. Metals also have a shiny appearance. They are good conductors of heat and electricity.

Elements on the right side of the periodic table are non-metals. Non-metals can be solids, liquids or gases at room temperature. They are poor conductors of heat and electricity.

Elements that have some metallic as well as non-metallic properties are known as metalloids (e.g., silicon, arsenic, etc.).

We sometimes call the elements in groups 3 to 12 the d-block. These elements are also known as transition elements.

Elements of the d-block from the periodic table of elements
Elements of the d-block from the periodic table of elements (Source: Let’s Talk Science using an image by Dmarcus100 [CC-BY-SA] via Wikimedia Commons).

There are two rows placed at the bottom of the periodic table. These are the Lanthanide and Actinide series. The Lanthanide series includes fifteen metallic elements with atomic numbers 57 through 71. The Lanthanide elements, along with the two elements of group 3, Scandium and Yttrium, are often called the rare earth elements. You can find Lanthanides naturally on Earth. The Actinide series is much different. All of the Actinide elements are radioactive and some are not found in nature. Some of the elements with higher atomic numbers can only be created in laboratories.

The lanthanide and actinides series of elements from the periodic table of elements
The lanthanide and actinides series of elements from the periodic table of elements (Source: Let’s Talk Science using an image by Dmarcus100 [CC-BY-SA] via Wikimedia Commons).

Trends of the Periodic Table

In general, the size or radius of an atom increases as you move down a group. As you go down, elements have more layers of electrons, which results in bigger atoms. From left to right within a period, atomic size generally decreases. This is because more protons pull the electrons closer to the nucleus.

Relative sizes of atoms
Relative sizes of atoms (Source: Let’s Talk Science using an image by the Encyclopedia Britannica).

Electronegativity is the chemical property that describes the tendency of an atom to form bonds with others. Electronegativity usually decreases down each group and increases from left to right across a period. The most electronegative elements are in the upper right hand side of the periodic table. This is because non-metals have high electronegativity. They tend to attract electrons from other atoms. While metals tend to lose electrons easily.

Assigning Charges to an Element

To become electrically-charged, stable atoms must lose or gain electrons. There are two types of electric charges. There are positive charges (+) and negative charges (-). Substances with the same charge will repel each other. While substances with opposite charges attract each other. This is similar to how magnets work!

The atoms of some elements can lose or gain electrons more easily than others. For example, the elements in group 1 (e.g., Li, Na, K) can easily lose one electron, which gives them a +1 charge. The elements in group 17 (Cl, Br, I) can easily gain one electron, which gives them a -1 charge. When an atom or molecule has a charge, it is said to be an ion. When an atom or molecule has more electrons than protons, the result is a negative ion, called an anion. When it has fewer electrons than protons, then the result is a positive ion, called a cation.

Each group in the periodic table has a specific charge commonly associated with its ions. The exceptions to this are the transition elements, and the lanthanide and actinide series. Below are the charges for the different groups within the table.

Group 1 2 3 Transition elements, Lanthanide and Actinide series 15 16 17 18
Charge +1 +2 +3 Various -3 -2 -1 0

You may have noticed that the elements in group 18 have a charge of 0. This is because these elements are very stable and they do not readily gain or lose electrons.

Learn More

The photographic periodic table
This page by periodictable.com has photographs of common things made from, or using, each of the element.

Introduction to the Particle Theory of Matter
This article from Let’s Talk Science introduces the history of the theory that describes matter as different assemblies of smaller particles, or atoms.

The Genius of Mendeleev's Table
This article from Let’s Talk Science presents how Dmitri Mendeleev created the first periodic table.

Introduction to the Atom
This article from Let’s Talk Science presents the history of the different atomic models created.

The Newest Elements on the Periodic Table
This article from Let’s Talk Science presents the most recent elements added to the periodic table.

The Periodic Table of Elements
This page by the Thomas Jefferson National Accelerator Facility has an interactive periodic table as well as flash cards, games, etc. about the elements.

References

Helmenstine, A. (2019). Introduction to the Periodic Table. Thought.co.

Webelements.com. (n.d.). The periodic table of the elements.

Western Oregon University. (n.d.). A Brief History Of The Development Of Periodic TablePeople.wou.edu