The four transition series
Which d sublevel fills in each period
1. The transition elements and their series
2. Period 4, but 3d?
Iron is in period 4, but its series fills the 3d sublevel. Why not 4d?
Pick the right answer
Predict: the second transition series is in period 5. Which sublevel does it fill?
- A. 5d
- B. 4d
- C. 5s
Explanation
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.
3. Four horizontal series
transition series
A horizontal series of main transition elements in which a d sublevel is filled successively.
period n \;\; (n-1)d
Why one less? In the filling order, 3d comes after 4s. So 3d fills only in period 4, after 4s.
4. Explore each series
Slide through the four series.
Transition series 1
Period 4
Sublevel filled 3d
The first transition series: period 4, the (3d) sublevel. Ten elements, from scandium ₂₁Sc (4s²\ 3d¹) to zinc ₃₀Zn (4s²\ 3d¹⁰). They come after calcium.
Element table
Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn
- Sc: first
- Zn: last
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.
Fill in the blanks
Zirconium (Zr) is in period 5. It is in the _____ transition series, which fills the _____ sublevel.
Explanation
Period 5 → (5-1)d = 4d, which fills in the second transition series.
6. Sort into series
Tap the table to read each element's period. Then sort.
Element table
Ti, Co, Mo, Ag, W, Pt, Rf
Sort into groups
Which transition series is each element in?
TiCoMoAgWPtRf
7. First and last
Pick the right answer
Which element starts the second transition series?
- A. Strontium, Sr
- B. Yttrium, Y
- C. Zirconium, Zr
- D. Scandium, Sc
Explanation
Yttrium, ₃₉Y (5s²\ 4d¹), starts the second transition series: it is the first element of period 5 with a 4d electron.
Pick the right answer
A student writes: 'The first transition series fills 4d, because it is in period 4.' What is wrong?
- A. It fills 3d: in period n, the (n−1)d sublevel fills
- B. It is in period 1, not period 4
- C. Nothing: period 4 fills 4d
Explanation
The first transition series fills 3d, not 4d: in period n the (n−1)d sublevel fills, because 3d comes after 4s in the filling order. Its first element, Sc, is 4s²\ 3d¹.
8. Summary
- Four horizontal series. A d sublevel is filled successively: 3d (period 4), 4d (period 5), 5d (period 6), 6d (period 7).
- 1st: ₂₁Sc (4s²\ 3d¹) to ₃₀Zn (4s²\ 3d¹⁰). 2nd: ₃₉Y (5s²\ 4d¹) to ₄₈Cd (5s²\ 4d¹⁰).
- 3rd: ₅₇La (6s²\ 5d¹) to ₈₀Hg (6s²\ 4f¹⁴\ 5d¹⁰).
Can you explain why the series in period 4 fills 3d, not 4d?
Reveal
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.