# Definition of the transition element

> Two places to look for an incomplete d sublevel


## Objectives

- State the book's definition of the transition element.
- Apply both tests: first the atom, then its oxidation states.
- Show that scandium is a transition element (atom $3d^1$), though $\ce{Sc^{3+}}$ has no d electrons.

## 1. Electronic configurations and oxidation states




## 2. Is scandium in or out?

Predict: is scandium a transition element?

- Only as an atom, not in its compounds
- Yes ✓
- No: $\ce{Sc^{3+}}$ has no d electrons

Scandium is a transition element. The book's definition also checks the atom: the Sc atom is $3d^1$, an incomplete d sublevel, even though $\ce{Sc^{3+}}$ has no d electrons.

[ar-EG] الـ scandium يعتبر transition element. تعريف الكتاب بيبص على الذرة كمان: ذرة الـ Sc فيها $3d^1$، يعني d sublevel مش مكتمل، حتى لو الـ $\ce{Sc^{3+}}$ مفيهوش d electrons.
## 3. The book's definition

Transition element The element in which the orbitals of d or f contain electrons but they are not complete, in its atomic state or in one of its oxidation states. The definition as two tests (book p.10) Incomplete means 1 to 9 d electrons. Being in the d-block is not enough: a full $d^{10}$ fails. The f case is for inner transition elements.


## 4. Complete or not?

Slide the number of d electrons. When is the d sublevel incomplete? d electrons $d^0$: the d orbitals contain no electrons. Test failed. $d^{1}$: incomplete. Test passed. $d^{2}$: incomplete. Test passed. $d^{3}$: incomplete. Test passed. $d^{4}$: incomplete. Test passed. $d^{5}$: incomplete. Test passed. $d^{6}$: incomplete. Test passed. $d^{7}$: incomplete. Test passed. $d^{8}$: incomplete. Test passed. $d^{9}$: incomplete. Test passed. $d^{10}$: complete. Test failed; check another state.


## 5. Worked: scandium; your turn: manganese

Step 1: Test the atom 3d holds one electron: incomplete. Scandium passes on the atom alone. Step 2: Does Sc³⁺ change the verdict? No. $\ce{Sc^{3+}}$ is [Ar], with $3d^0$. But the definition says atom OR one of its oxidation states. One pass is enough. Your turn: manganese $\ce{_{25}Mn}$: [Ar] $4s^2$ 3d___ . In $\ce{KMnO4}$ (+7), the Mn has 3d___ .


## 6. Sort the elements

Sort each element with the book's definition.


## 7. Titanium in TiO₂

In $\ce{TiO2}$, titanium is +4, so its d sublevel is empty ($3d^0$). A student says titanium is therefore not a transition element. What is wrong?

- Ti in +4 still keeps its 4s electrons
- The definition is met by the atom or one of its states, and the Ti atom is $3d^2$ ✓
- Nothing: an element with a $3d^0$ state is not transition

The definition is met when the d sublevel is incomplete in the atom or in any one of its oxidation states. The Ti atom is $3d^2$, so titanium is a transition element even though Ti(+4) is $3d^0$.

[ar-EG] التعريف بيتحقق لو الـ d sublevel مش مكتمل في الذرة أو في أي oxidation state من بتوعها. وذرة الـ Ti فيها $3d^2$، فالـ titanium يعتبر transition element حتى لو الـ Ti(+4) بقى $3d^0$.
## 8. Summary

A transition element has d (or f) orbitals that contain electrons but are not complete. Test the atom first; if it fails, test its oxidation states. One pass is enough. Scandium is a transition element: its atom is $3d^1$, though $\ce{Sc^{3+}}$ is $3d^0$. Define: the transition element It is the element in which the orbitals of **d or f contain electrons** but they are **not complete** in its **atomic state** or in **one of its oxidation states**. Next: copper's atom is $3d^{10}$ like zinc's, yet copper is a transition element. Why? Can you explain why scandium counts, though $\ce{Sc^{3+}}$ has no d electrons? Scandium's atom is $3d^1$: its d orbitals contain electrons but are not complete, so the atom passes the test. One pass is enough, though $\ce{Sc^{3+}}$ is $3d^0$.



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