☰ Year plan · Chemistry

The d block and the first series in use

Week 1 · Chapter 1 Transition Elements (A): chapter opener and objectives, the d block and the four transition series, the first series Sc to Zn and the uses of each element (light, descriptive week) · 3 lessons
1

The d block and the four transition series

Chemistry Sec 3 Term 1, Chapter 1: pp. 1–8
GoalSay where the transition elements sit in the periodic table, why the d block has ten columns, and name the four series and the ten elements of the first one.
New words
transition element (d block) · an element of the middle block of the periodic table, where the d sublevel is being filled; week 2 gives the exact testseries · a horizontal row of ten d block elements in one periodinner transition elements (f block) · the two long rows of f sublevel elements, only mentioned in this course
Explanation

Look at the long form of the periodic table. On the left is the s block (groups 1 and 2) and on the right the p block (groups 13 to 18). Between them, from period 4 downwards, sits the d block: the transition elements (counting the inner transition elements too, more than 60 elements, over half of all the elements known). In each of them the electrons being added go into a d sublevel. A d sublevel has five orbitals and holds at most 10 electrons, so each series has ten elements and the block has ten columns, groups 3 to 12 (in the older numbering IIIB, IVB, VB, VIB, VIIB, then three columns together called VIII, then IB and IIB). The three VIII columns (8, 9, 10) resemble one another along a row more than they resemble the elements below them. There are four horizontal series: the 3d series, Sc to Zn, in period 4; the 4d series, Y to Cd, in period 5; the 5d series, from La to Hg, in period 6; and the 6d series in period 7, which is incomplete. The f block (inner transition elements) is only mentioned here. In this course we study the first series.

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Worked examples
Find a series from the atomic number. Iron has Z = 26. After argon (18) and calcium (20) the 3d sublevel starts filling at scandium (Z = 21), so iron is the 26 − 20 = 6th element of the 3d series, in period 4. Check by counting: Sc 21, Ti 22, V 23, Cr 24, Mn 25, Fe 26.
SeriesSublevel fillingPeriodStartsEnds
first3d4ScZn
second4d5YCd
third5d6LaHg
fourth6d7incompleteincomplete
A different series. Yttrium (Y, Z = 39) starts the 4d series in period 5. Molybdenum has Z = 42, so it is the 42 − 38 = 4th element of that series. The series has ten elements, so it ends at Z = 39 + 9 = 48, cadmium.
SublevelOrbitalsMost electronsElements in a row
s122
p366
d51010
f71414
Why ten, and not eight or fourteen? The number of elements in a row equals the number of electrons the sublevel can hold: orbitals × 2. A d sublevel has 5 orbitals, so 5 × 2 = 10 elements in each series and 10 columns. The same rule gives 2 for s, 6 for p and 14 for f.
Class activity

Build the middle of the table on squared paper. Draw a row of ten boxes and write the ten symbols with the atomic numbers 21 to 30: Sc, Ti and V first, then Cr and Mn, then Fe, Co and Ni, then Cu and Zn (check them in any periodic table). Under it draw a second row of ten boxes for the 4d series, starting with Y (39) and ending with Cd (48). Colour the three boxes under Fe, Co and Ni in both rows, and write one sentence on why chemists treat these three columns as one group.

Practice
1
Why does the d block have ten columns?
2
Copper has Z = 29. Which series is it in, and which element of that series is it?
3
Ruthenium is the 6th element of the 4d series, which starts with yttrium (Z = 39). What is its atomic number?
4
A pupil says: “The d block is just another name for all the metals.” Is that right? Give one reason.