Transition series

It is an essential subject that helps one understand the characteristics of different elements in the periodic table, as well as their relationships with other compounds and atoms. The two most common types of transitions are single-atom (or atom-level) and double-atom (or d-level). In this article, we will take a closer look at both and explain where they occur in nature and how they can be used to synthesize various compounds.

Single-atom transitions are changes in the number or type of electrons in an atom from one valence electron to another. For example, an atom with 2 valence electrons would lose a single electron, and a single atom without any valence electrons would gain a single electron. Single-atom transitions often occur naturally in many different molecules, including water, carbon dioxide, and methane, among others. They can also be generated experimentally, for example, by bombarding an atom with high-energy lasers or ultraviolet flashes.


Double-atom transitions are larger than single-atom transitions. They involve the removal or addition of multiple electrons to an atom at once, such as in compounds like hydrogen cyanide or lithium bromide. Double-atom transitions can occur in several ways, such as through fission (the splitting of an atom into two smaller particles), evaporation (the absorption of energy by molecules), or proton-electron reactions (the pairing of electrons in a compound). These processes have been known for centuries, but new research has led to improvements in their understanding.

Suppose a reaction between oxygen and hydrogen. In first step, when you combine oxygen with hydrogen, the process begins with the release of an electron:

This causes the bond between the two atoms to split into two separate compounds, which is also called a ‘scission’:

The next step involves adding a second electron to this newly created molecule:

This causes the bond between the two atoms to become more stable, forming a ‘molecule,’

During further chemical reactions, these two molecules may fuse:

To create a compound composed of more than one element, we typically need to add additional electrons to fill gaps between the two. This can be achieved through the use of catalysts such as metals or ceramics, or through the addition of nuclei to other elements. Another way to achieve multiple elements in a compound is through radioactive decay — the formation of a heavier nucleus when one element decays into a lighter atom (such as when uranium decayed into a form of less than 100U, leaving behind only the more stable isotope of Uranium 99U).

Transitioning from One Molecule to Another Is Just Like That!

To illustrate this point, let’s consider the following example: Suppose a simple molecule consists of just three atoms. It’s not very complex, but it shows how easy it is to change from one element to another. Let’s assume we want to make a simple mixture of hydrogen and oxygen. First, we need to remove hydrogen from one end of the molecule:

We’ll call this the first position — it’s just hydrogen. Next, we need to replace oxygen with hydrogen near the middle of the molecule:

This means moving the oxygen to the right side of the molecule at the last location, where it will meet with the third hydrogen. This is illustrated by the arrow in the diagram above:

Finally, we need to replace the third hydrogen with pure oxygen.

The key to understanding this transition is that we know that atoms move around in space in straight lines. Therefore, if we draw a line in the middle of the diagram, it will follow the same path as the hydrogen molecule. This means that we can predict where a new hydrogen atom will go based on the previous hydrogen atoms. Now let’s imagine that we draw a line along the middle of the diagram, following the same path to the right, and so on until we reach the final hydrogen atom. If the hydrogen atom is added at any point along this line, the hydrogen atom immediately adjacent to the new one will be removed. On the other hand, if the new hydrogen atom is removed from the center of the diagram (on the left side of the diagram), it will leave the center unchanged.

To summarize this section, when a hydrogen atom moves from one end of the molecule to the other, it gains or loses a single hydrogen at the new location. But if the hydrogen atom is moved to the opposite end (left of the molecule), it gains a single hydrogen at the original location and loses a single hydrogen in the new location.