Q.La belongs to group 3 while Hg belongs to group 12 and both belong to period 6 of the periodic table. Write down the general outer electronic configuration of the ten elements from La to Hg together using orbital notation method.

Step 1. Identify the ten elements. In period 6, the elements occupying groups 3 to 12 are La(57), Hf(72), Ta(73), W(74), Re(75), Os(76), Ir(77), Pt(78), Au(79) and Hg(80) — the lanthanoid series (Ce to Lu, atomic numbers 58-71) is placed separately at the bottom of the table and is not counted among these ten (section 7.2).

Step 2. Recall the d-block general pattern. Section 7.3.3 gives the d-block's general outer configuration as $ns^{0-2}(n-1)d^{1-10}$; for period 6 this becomes $6s^{0-2}5d^{1-10}$, filling from La's $6s^25d^1$ up to Hg's $6s^25d^{10}$.

Step 3. Note the known anomaly within this range. As worked out in Problem 7.3, Au (group 11) does not follow the plain pattern: its outer configuration is $6s^15d^{10}$ rather than the 'expected' $6s^25d^9$, because a completely-filled 5d subshell is extra stable — exactly the same kind of exception noted for Cr and Cu in the period-4 d-block.

Step 4. State the overall pattern. Using orbital notation, the ten elements' outer configurations run: La $6s^25d^1$, Hf $6s^25d^2$, Ta $6s^25d^3$, W $6s^25d^4$, Re $6s^25d^5$, Os $6s^25d^6$, Ir $6s^25d^7$, Pt $6s^25d^9$ (Pt is also anomalous, favouring a near-filled d subshell), Au $6s^15d^{10}$, Hg $6s^25d^{10}$.

Applying the d-block general outer configuration pattern to the ten period-6, groups-3-to-12 elements, and flagging the known anomaly

• Including the 14 lanthanoid elements (Ce to Lu) in this count, mistaking them for part of the 'ten elements from La to Hg' — they are placed in a separate row and are not part of period 6's groups 3-12.
• Presenting a perfectly uniform $6s^25d^{1-10}$ pattern without acknowledging the Au (and Pt) anomalies already established elsewhere in the chapter (Problem 7.3).