What is the name given to elements that are in the fifth period and whose 4d subshells are filled successively?
The phrase fifth period refers to the fifth period of the periodic table. The word period refers to a row. The fifth period is the fifth row. In order to answer the question, we need to know which elements are having their 4d subshells filled successively. We know that the block on the left, where we find the alkaline and alkaline earth metals, is the s block. The block on the far right is the p block. And the block in the middle of the periodic table is the d block.
So what we’re looking for is the intersection of the fifth period with the d block. That’s this section here. That’s the elements yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, and cadmium. The d block contains what I call the transition elements. So the top line of the d block is sometimes called the first transition series. So it follows that the intersection of fifth period with the d block is called the second transition series. So the name given to elements that are in the fifth period whose 4d subshells are filled successively is the second transition series.
However, just to be safe, let’s have a look at the electronic configuration of the second transition series elements and reassure ourselves that it is the 4d subshell that is being filled. Instead of going directly there, let’s have a look at the electronic structure of krypton. The electronic configuration of krypton is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶. The order of subshells in krypton’s electronic configuration show the Aufbau principle where electrons occupy the orbital with the lowest energy first. 1s, 2s, 2p 3s, 3p 4s, 3d 4p.
The next subshell to be filled is the 5s subshell that corresponds to rubidium and strontium. This means that the next subshell to be filled is the 4d subshell. This means that the general formula for the electron configuration of the second transition series of elements is krypton 5s² 4dⁿ where, for ruthenium, 𝑛 equals one, zirconium, 𝑛 equals two, niobium, 𝑛 equals three, and so on. So what we’re seeing is the successive filling of the 4d subshell.
There are some inconsistencies where a single electron from the 5s subshell is promoted into the 4d subshell making a half-filled or filled subshell. But in the main, we’re looking at successive population. So we’ve demonstrated that elements in the fifth period in the d block are having their 4d subshells successively filled and that the name for these elements is the second transition series.