How Is The Periodic Table Organized And Arranged?

Image source: Wikipedia

One of the things that science students must learn is the periodic table. How is the periodic table organized? The periodic table is organized like a grid.


In this article, we will explain how the grid organizes the elements. Understanding how the elements are organized in the grid may help you to learn the periodic table.

The position of each of the elements is not at all random but due to its atomic structure.

Grid Structure

As with all grid structure, the periodic table has both columns from up and down and rows from left to right. The rows and columns are organized by precise characteristics. The elements that are in the same column or in the same rows have common characteristics. For example, magnesium (Mg) and sodium (Na) share some qualities because they have similar electron configurations. When elements have similar electron configurations, they are said to be in the same period.

But that only accounts for the rows. Columns are organized into groups of elements that have similar chemical properties. For example, potassium (K) and rubidium (Rb) are on the first row, which means that they are in the same group.

Image source: Wikipedia

The chemical elements are also arranged in increasing number by atomic number.

If studying the periodic table taught me nothing else, it’s that the credulity of human beings for periodic table panaceas is pretty much boundless. – Sam Kean


Let us investigate periods. After all, that is how the periodic table gets its name. Each of the rows from left to right is called a period. What that means in that each and every one of the elements in a row shares similar electron configurations with the others. Or, in other words, each of the elements in the same row has the exact same number of atomic orbitals.

If you look at all the elements on the top row or, in other words, the elements in the first period, you will see that all of them have one atomic orbital for their electrons. Then, the elements on the second row, or second period, are characterized by having two atomic orbitals in their electrons. For every other row or period, you would need to add another atomic orbital.

If you know how many atomic orbitals a specific element has, you should be able to know what row it sits at. Another way of looking at it is that if you know what row an element occupies in the periodic table, you should be able to tell how many atomic orbitals that specific element has (1, 2, 3, etc.).

Image source: Wikipedia


Now, let us look at groups. All the chemical elements in the same column (from top to bottom) belong to the same group. In fact, every column is called a group. But, how are the elements “grouped” together?

All the elements in each group have the same number of electrons in their outer orbitals, also known as valence electrons. These electrons are important because they are involved in the chemical bonds with other elements.

You have to read groups from left to right. All the elements in the first column, or group one, have one valence electrons (one electron in their outer shell). All the elements in the second column, or group two, have two valence electrons. But all the elements in the third group (group three), have thirteen valance electrons. From then on, you have to add an electron for every group until reaching 18. Simply, counting the columns will allow you to know how many electrons each element has on its outer shell. There are a few exceptions to this, though, because some elements are transition elements that add electrons.

There are 8 different groups:


Group 1 is for Alkali Metals: lithium (li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr).

Group 2 is for Alkaline Earth Metals: beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). Radium is not always thought of as an alkaline on earth because of its radioactivity.

Group 13 is the Boron group: boron (B), aluminum (Al), gallium (Ga), indium (In), thallium (Tl), and, sometimes, ununtrium (Uut).

Group 14 is the Carbon group: carbon (C) silicon (Si), germanium (Ge), tin (Sn), lead (Pb), and, sometimes, ununquadium (Uuq).

Group 15 is the Nitrogen group: Nitrogen (N), Phosphorus (P), Arsenic (As), Antimony (Sb), Bismuth (Bi)m and, sometimes ununpentium (UUp).

Group 16 is for Chalcogens, also sometimes known as the oxygen group: Oxygen (O), sulfur (S), selenium (Se), tellurium (Te), polonium (Po), and ununhexium (Uuh).

Group 17 is for Halogens: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and, sometimes, ununseptium (Uus).

Group 18 is for Noble Gases: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Ra).

Each of these groups has shared properties that can be studied in a lot more detail but it is not necessary to know them in order to see how the periodic table is organized.

Image source: Wikipedia

The Two Elements At the Top

You are probably wondering about the elements that are alone on the top: hydrogen (H) and helium (He). These two are special elements for different reasons.

Hydrogen (H) does not have a single neutron in its neutral form, only one proton and one electron. Now, atomic hydrogen needs to be combined with other elements in order to get its outer shell filled.

Helium (He) is unique among all the elements. It only has two electrons in its outer orbital, also known as the valence shell. All the other noble gases (group 18) have eight electrons in their outer orbital or valence shell. So, why is helium group with neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Ra)? Because they all have one thing in common: their respective valence shells are full.

This is how the periodic table is organized. Understanding that the position of each and every one of the elements is useful in understanding their properties. If you are trying to memorize the periodic table or if you have to study the elements as part of a science group, knowing that the positions of the elements is not random but follows a very tight logic might help you in your academic endeavors.

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Juan Ramos, MA. How Is The Periodic Table Organized And Arranged?, Science Trends, 2018. Available at:
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