Animated Solution for Chemistry - Periodicity in Properties: The element with $Z=120$ (not yet discovered) will be an/a

Imagine standing at the very edge of the known chemical universe. The periodic table, as we know it, ends at element $118$. But what lies beyond?

Predicting the properties of undiscovered elements is one of the most fascinating applications of periodicity. In this problem, we are tasked with finding the family of element $120$.

To do this, we don't need to memorize complex quantum mechanics; we just need to follow the elegant, repeating patterns of the periodic table.

Our journey begins with the heaviest element discovered so far: Oganesson ($\text{Og}$).

Oganesson has an atomic number of $Z=118$. Because it completes the $7\text{p}$ subshell, it sits proudly at the very bottom of Group $18$.

This makes it a noble gas, and more importantly, it marks the absolute end of the $7^{\text{th}}$ period. Any element with an atomic number greater than $118$ must spill over into a brand new row.

Now, let's add protons one by one.

If we create element $119$, where does it go? Since the $7^{\text{th}}$ period is completely full, element $119$ must start the $8^{\text{th}}$ period. It will be placed in Group $1$, making it an alkali metal with a valence configuration of $8{\text{s}}^1$.

Following this exact logic, we add one more proton to reach our target: element $120$.

Element $120$ will sit right next to element $119$. This places it squarely in Group $2$ of the $8^{\text{th}}$ period.

We can also confirm this by writing out its predicted electronic configuration.

Since element $120$ comes exactly two spots after the noble gas Oganesson, its core will be identical to $[\text{Og}]$. The two additional electrons will fill the next available orbital, which is the $8\text{s}$ orbital.

Therefore, the general electronic configuration for element $120$ is:

In the periodic table, the group number dictates the chemical family.

Elements in Group $1$ are alkali metals, and elements in Group $2$ are alkaline earth metals. Because element $120$ has an $n{\text{s}}^2$ valence shell and resides in Group $2$, it will undoubtedly be an alkaline earth metal.

This simple yet powerful deduction shows why the periodic table is considered one of the greatest achievements in science—it allows us to accurately predict the future!