[ A_r = \frac(\textIsotope 1 mass \times \textabundance) + (\textIsotope 2 mass \times \textabundance)100 \text (or total abundance) ]
Depending on your level, covers two types of electronic configuration: GCSE (2,8,8,2) and A-Level (1s² 2s² 2p⁶).
A mass spectrometer shows a sample of Rubidium has peaks at mass 85 (72%) and mass 87 (28%). Calculate Ar. Answer: (85 72)+(87 28) / 100 = (6120 + 2436) / 100 = 85.56 chemsheets atomic structure
Even with a perfect worksheet, students fall into specific pits. Here is what Chemsheets flags in their teacher notes.
Chemsheets excels here because their worksheets require you to calculate using isotopic abundance data. [ A_r = \frac(\textIsotope 1 mass \times \textabundance)
Mass number = Protons + Neutrons = 11 + 12 = 23 (This is Sodium-23).
Decreases because the outer electron is further from the nucleus and more shielded. Answer: (85 72)+(87 28) / 100 = (6120 + 2436) / 100 = 85
The shift from the "shell" model (GCSE) to the "sub-shell/orbital" model (A-Level) is one of the most difficult conceptual leaps in chemistry. The Chemsheets Atomic Structure resources provide clear, visual ways to learn this.
Draw the electronic configuration for Calcium (Atomic number 20). Answer: 2, 8, 8, 2