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UAT-UK SPEC: C1MODULE: CHEMISTRYTOPIC ID: ARCH-C-01

Subatomic Isoelectronic Ions, Isotopic Aᵣ Weighted Means & Comma Electron Configs (Z ≤ 20)

Master Subatomic Isoelectronic Ions, Isotopic Aᵣ Weighted Means & Comma Electron Configs (Z ≤ 20) on the ESAT Chemistry paper. Traditional classroom derivations waste valuable seconds. Using the 2-step Sub-90 invariant elimination method compresses solve time to 30s, saving +95s per question.

Standard Classroom Time
125s
Textbook multi-line derivations bleed exam clock
Sub-90 Target Pace
30s
Comfortably below the 88.8s per-question limit
Time Saved for Review
+95s
Banks clock buffer across 27 questions

2-Step Sub-90 Shortcut Formula

How to eliminate intermediate algebra and solve under 45 seconds.

Launch Interactive Lesson
STEP 1 • SETUP INVARIANT (LINE 1)10–15s
Line 1 (Charge & Shell Prune): N3−\text{N}^{3-} has 7+3=10 e−→2,87 + 3 = 10\text{ e}^- \rightarrow 2,8 (isoelectronic with Ne\text{Ne}).

Establish the structural invariant and eliminate impossible options immediately.

STEP 2 • FAST SOLVE (LINE 2)15–25s
Line 2 (Neutron Check): n=15−7=8→n = 15 - 7 = 8 \rightarrow 7 protons | 8 neutrons | 2,8 (25s).

Evaluate the simplified expression using integer factoring or unit elimination.

Distractor Trap Forensics

The predictable cognitive traps engineered by examiners into the wrong options.

TRAP #1sign_or_direction_flip

Adding electrons for a positive cation M²⁺ (Z + 2) or subtracting electrons for an anion X²⁻ (Z - 2)

Inverting the negative charge of an electron when adjusting ion electron counts.

Sub-90 Fix: Test invariants before expanding equations.
TRAP #2fence_post_or_domain_trap

Confusing neutron count (A - Z) with mass number A or proton number Z

Reading nucleon number A directly as neutron number.

Sub-90 Fix: Test invariants before expanding equations.
TRAP #3table_column_pruning_trap

Checking mass numbers before pruning rows via Group number = outer shell electron count (e.g. Group 16 = 6 outer electrons)

Not using the IUPAC Group 1-18 outer-shell shortcut to eliminate 75% of rows instantly.

Sub-90 Fix: Test invariants before expanding equations.

Try 1 Timed Question: Subatomic Isoelectronic Ions, Isotopic Aᵣ Weighted Means & Comma Electron Configs (Z ≤ 20)

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Full Lesson All 15 Questions (ARCH-C-01)
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ARCH-C-01: Subatomic Isoelectronic Ions, Isotopic Aᵣ Weighted Means & Comma Electron Configs (Z ≤ 20) (Sample)Chemistry
00:00.0
SUB-90 ZONE (<25S)
0.0s25s Sub-9090s ESAT Budget150s Classroom
Question 1 of 1ARCH-C-01 (6-Card Lesson)Format: Table-Row Matching
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Question 1 of 1 • 90s Target

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