# The four transition series

> Which d sublevel fills in each period


## Objectives

- Name the four transition series and the sublevel filled successively in each: 3d, 4d, 5d, 6d.
- Link each series to its period (4, 5, 6, 7): in period n, the (n−1)d sublevel is filled.
- Name the first and last element of the first three series, with their configurations as in the book.

## 1. The transition elements and their series




## 2. Period 4, but 3d?

Predict: the second transition series is in period 5. Which sublevel does it fill?

- 5s
- 5d
- 4d ✓

The second transition series fills 4d. In period n the (n−1)d sublevel fills, because in the filling order 3d comes after 4s and 4d comes after 5s.

[ar-EG] الـ second transition series بتملا الـ 4d. في الـ period n بيتملي الـ (n−1)d sublevel، عشان في ترتيب الملء الـ 3d بييجي بعد الـ 4s، والـ 4d بييجي بعد الـ 5s.
## 3. Four horizontal series

transition series A horizontal series of main transition elements in which a d sublevel is filled successively. period 4 → 3d, period 5 → 4d, period 6 → 5d, period 7 → 6d Why one less? In the filling order, 3d comes after 4s. So 3d fills only in period 4, after 4s. The first transition series fills 4d because it is in period 4.


## 4. Explore each series

Slide through the four series. Transition series Period Sublevel filled **The first transition series**: period 4, the (3d) sublevel. Ten elements, from scandium $\ce{_{21}Sc}$ $(4s^2\ 3d^1)$ to zinc $\ce{_{30}Zn}$ $(4s^2\ 3d^{10})$. They come after calcium. **The second transition series**: period 5, the (4d) sublevel. Ten elements, from yttrium $\ce{_{39}Y}$ $(5s^2\ 4d^1)$ to cadmium $\ce{_{48}Cd}$ $(5s^2\ 4d^{10})$. **The third transition series**: period 6, the (5d) sublevel. Ten elements, from lanthanum $\ce{_{57}La}$ $(6s^2\ 5d^1)$ to mercury $\ce{_{80}Hg}$ $(6s^2\ 4f^{14}\ 5d^{10})$. On this table, La sits in the bottom row. **The fourth transition series**: period 7, the (6d) sublevel. Why $4f^{14}$ in Hg? The lanthanides, after La, fill the 4f sublevel. Hg keeps those 14 electrons.


## 5. Find the series

Gold (Au) is in period 6. Which series is it in? Step 1: find the sublevel Rule: in period n, the (n−1)d sublevel fills. Period 6 → $(6-1)d$ = 5d. Step 2: find the series The 5d sublevel fills in the third transition series. So Au is in the third series. Your turn Zirconium (Zr) is in period 5. It is in the ___ transition series, which fills the ___ sublevel.


## 6. Sort into series

Tap the table to read each element's period. Then sort. Which transition series is each element in?


## 7. First and last

Which element starts the second transition series? A student writes: 'The first transition series fills 4d, because it is in period 4.' What is wrong?


## 8. Summary

Four horizontal series. A d sublevel is filled successively: 3d (period 4), 4d (period 5), 5d (period 6), 6d (period 7). 1st: $\ce{_{21}Sc}$ $(4s^2\ 3d^1)$ to $\ce{_{30}Zn}$ $(4s^2\ 3d^{10})$. 2nd: $\ce{_{39}Y}$ $(5s^2\ 4d^1)$ to $\ce{_{48}Cd}$ $(5s^2\ 4d^{10})$. 3rd: $\ce{_{57}La}$ $(6s^2\ 5d^1)$ to $\ce{_{80}Hg}$ $(6s^2\ 4f^{14}\ 5d^{10})$. **The first transition series**: the elements in which the sublevel **(3d) is filled successively**. Found in the **fourth period after calcium**; ten elements, from scandium to zinc. Can you explain why the series in period 4 fills 3d, not 4d? In the filling order, 3d comes after 4s. So 3d fills only in period 4, after 4s: in period n, the (n−1)d sublevel fills.



Chapter: Transition Elements (https://yaani.ai/ar/learn/chemistry/chem-s3-en.ch1)
Source: https://yaani.ai/ar/lesson/chem-s3-en.lesson-te.transition-series