The elements with atomic numbers 101 and 104 belong to, respectively,
(a) actinoids and group 4
(b)

Q: Why isn't $Z=104$ in Group 3?

Group 3 in the 7th period contains Actinium ($Z=89$). After Actinium, the next 14 elements ($Z=90$ to $103$) are the actinoids, which are placed in the f-block at the bottom of the periodic table. Once the f-block is full, the sequence returns to the d-block, starting with Group 4 for $Z=104$.

Q: Do I need to memorize the entire periodic table for JEE?

Not the entire table, but you absolutely must memorize the atomic number ranges for the s-block, p-block, and especially the starting and ending points of the Lanthanoid ($58-71$) and Actinoid ($90-103$) series.

Q: What is the electronic configuration of $Z=104$?

Element 104 (Rutherfordium) has the noble gas core of Radon ($Z=86$). Its configuration is $[\text{Rn}] 5f^{14} 6d^2 7s^2$. The presence of 2 electrons in the d-subshell and 2 in the s-subshell places it in Group $2+2=4$.

Q: Are actinoids transition metals?

Actinoids are classified as *inner* transition metals because their last electron enters the anti-penultimate $f$-orbital ($n-2$). Regular transition metals have their last electron entering the penultimate $d$-orbital ($n-1$).

Q: How can I quickly find the group number for elements > 103?

For elements with $Z > 103$, the group number is simply the last two digits of the atomic number! For example, $Z=104$ is in Group 4, $Z=105$ is in Group 5, and $Z=118$ is in Group 18.

Question

The elements with atomic numbers 101 and 104 belong to, respectively,

Options:

(A) actinoids and group 4

(B) actinoids and group 6

(C) group 6 and actinoids

(D) group 11 and group 4

Sigma Percentile · Accepted Answer

### The Map of the Elements

The periodic table is not just a chart; it is a beautifully organized map of the universe's building blocks. When we are asked to find the position of elements with atomic numbers $Z = 101$ and $Z = 104$, we don't need to guess. We just need to read the map!

Let's break down the geography of the periodic table, specifically focusing on the heavyweights at the very bottom.

### The Hidden Basement: The f-block

If you look at the standard periodic table, you'll notice two rows pulled out and placed at the bottom. This is the **f-block**. It consists of two series: the Lanthanoids and the Actinoids.

The Actinoid series is the second row of this basement. It begins with Thorium at $Z = 90$ and stretches all the way across 14 elements, ending with Lawrencium at $Z = 103$.

Knowing this range is an absolute superpower for JEE chemistry!

### Placing Element 101

Now, let's look at our first target: $Z = 101$.

Does it fall between $90$ and $103$? Yes, it does! It sits perfectly within the Actinoid series.

Therefore, element 101 (which is Mendelevium, named after the father of the periodic table himself) is an **Actinoid**. That was the easy part.

### The Leap to the d-block

What happens when we reach $Z = 103$? The f-block is completely full. There is no more room in the $5f$ subshell.

So, the very next electron for element $Z = 104$ must enter the $6d$ subshell. This means we are jumping back up into the main body of the periodic table, specifically into the **d-block** (the transition metals).

But which group does it land in?

Remember that Group 3 is the anchor point for the f-block. Actinium ($Z = 89$) is in Group 3, and then the 14 Actinoids branch off. Once they are done, the sequence resumes in the d-block.

Since Group 3 is already accounted for, the next available slot is **Group 4**. Therefore, element $Z = 104$ (Rutherfordium) belongs to Group 4.

### The Final Verdict

By simply knowing the boundaries of the f-block, we've solved the puzzle.

Element $Z = 101$ is an **Actinoid**, and element $Z = 104$ belongs to **Group 4**.

**Pro Tip:** For elements beyond $Z = 103$, the group number is simply the last two digits of the atomic number! So, $Z = 104$ is Group 4, $Z = 105$ is Group 5, and so on. Keep this trick up your sleeve to save precious seconds in the exam!

Animated Solution for Chemistry - d and f-Block Elements: The elements with atomic numbers 101 and 104 belong to, respectively,

Select Answer:

Visualized Solution

The Periodic Table

Actinoid Series Range

Position of $Z = 101$

Position of $Z = 104$

Final Conclusion

The Way Forward

The Sigma Insight: Inner Transition Elements

The Map of the Elements

The Hidden Basement

Placing Element 101

The Leap to the d-block

The Final Verdict

Similar Questions

The highest possible oxidation states of uranium and plutonium, respectively, are

The correct order of atomic radii is

Larger number of oxidation states are exhibited by the actinoides than those by the lanthanoides, the main reason being

The atomic radius of Ag is closest to

The electronic configuration of bivalent europium and trivalent cerium are (atomic number : $Xe = 54, Ce = 58, Eu = 63$ )

The actinoids exhibit more number of oxidation states in general than the lanthanoids. This is because

In context of the lanthanoids, which of the following statements is not correct?

The effect of lanthanoid contraction in the lanthanoid series of elements by and large means

The pair(s) of diamagnetic ions is(are)

The number of $4 f$ electrons in the ground state electronic configuration of $Gd^{2 +}$ is ...... . [Atomic number of Gd is 64.]