Definition of the transition element

Two places to look for an incomplete d sublevel

1. Electronic configurations and oxidation states

2. Is scandium in or out?

Scandium is the first element of the series. But

Sc³⁺ Sc X^{3 +}

, its only ion, has no d electrons at all.

Pick the right answer

Predict: is scandium a transition element?

A. Yes
B. No: $Sc³⁺ Sc X^{3 +}$ has no d electrons
C. Only as an atom, not in its compounds

Explanation

Scandium is a transition element. The book's definition also checks the atom: the Sc atom is

3d¹ 3 d^{1}

, an incomplete d sublevel, even though

Sc³⁺ Sc X^{3 +}

has no 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.

Atom: is the d sublevel incomplete ( $d¹ d^{1}$ to $d⁹ d^{9}$ )? → Transition element (yes)
Atom: is the d sublevel incomplete ( $d¹ d^{1}$ to $d⁹ d^{9}$ )? → Is d incomplete in one of its oxidation states? (no)
Is d incomplete in one of its oxidation states? → Transition element (yes)
Is d incomplete in one of its oxidation states? → Not a transition element (no)

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

d¹⁰ 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 0

d⁰ d^{0}

: the d orbitals contain no electrons. Test failed.

5. Worked: scandium; your turn: manganese

Step 1: Test the atom

₂₁Sc:\ [Ar]\ 4s²\ 3d¹

3d holds one electron: incomplete. Scandium passes on the atom alone.

Step 2: Does Sc³⁺ change the verdict?

No.

Sc³⁺ Sc X^{3 +}

is [Ar], with

3d⁰ 3 d^{0}

. But the definition says atom OR one of its oxidation states. One pass is enough.

Your turn: manganese

Fill in the blanks

₂₅Mn X_{25} X_{225}^{2} Mn

: [Ar]

4s² 4 s^{2}

3d_____ . In

KMnO4 KMnO X_{4}

(+7), the Mn has 3d_____ .

Explanation

Mn atom:

3d⁵ 3 d^{5}

, incomplete, so Mn is a transition element. Mn(+7) is

3d⁰ 3 d^{0}

, but one pass is enough.

Need a hint?

[Ar] holds 18 electrons; 4s holds 2.
For +7, start from 7 electrons in 4s and 3d.
4s leaves first, then 3d.

6. Sort the elements

Sort into groups

Sort each element with the book's definition.

$₂₂Ti X_{22} X_{222}^{2} Ti$ : [Ar] $4s²\ 3d²$ $₂₀Ca X_{20} X_{220}^{2} Ca$ : [Ar] $4s² 4 s^{2}$ ; only state +2: [Ar] $₃₁Ga X_{31} X_{231}^{2} Ga$ : [Ar] $4s²\ 3d¹⁰\ 4p¹$ ; state +3: [Ar] $3d¹⁰ 3 d^{10}$ $₂₇Co X_{27} X_{227}^{2} Co$ : [Ar] $4s²\ 3d⁷$ $₁₉K X_{19} X_{219}^{2} K$ : [Ar] $4s¹ 4 s^{1}$ ; only state +1: [Ar] $₃₀Zn X_{30} X_{230}^{2} Zn$ : [Ar] $4s²\ 3d¹⁰$ ; only state +2: [Ar] $3d¹⁰ 3 d^{10}$

7. Titanium in TiO₂

Pick the right answer

TiO2 TiO X_{2}

, titanium is +4, so its d sublevel is empty (

3d⁰ 3 d^{0}

). A student says titanium is therefore not a transition element. What is wrong?

A. The definition is met by the atom or one of its states, and the Ti atom is $3d² 3 d^{2}$
B. Nothing: an element with a $3d⁰ 3 d^{0}$ state is not transition
C. Ti in +4 still keeps its 4s electrons

Explanation

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

3d² 3 d^{2}

, so titanium is a transition element even though Ti(+4) is

3d⁰ 3 d^{0}

True or false?

To decide if an element is a transition element, we check only its neutral atom.

Explanation

'… in their atomic state or in one of their oxidation states' (book p.10).

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 $3d¹ 3 d^{1}$ , though $Sc³⁺ Sc X^{3 +}$ is $3d⁰ 3 d^{0}$ .

Next: copper's atom is

3d¹⁰ 3 d^{10}

like zinc's, yet copper is a transition element. Why?

Can you explain why scandium counts, though

Sc³⁺ Sc X^{3 +}

has no d electrons?

Reveal

Scandium's atom is

3d¹ 3 d^{1}

: its d orbitals contain electrons but are not complete, so the atom passes the test. One pass is enough, though

Sc³⁺ Sc X^{3 +}

3d⁰ 3 d^{0}

Concepts in this lesson