Chemistry IA · Structure 3 · Classification of matter · topic 11 of 25

Ionisation energies: where do the shells show? · IB Chemistry IA idea: guide, sample graph and step-by-step plan

no lab, so your thinking has to shine

A plot of successive ionisation energies is the nearest thing to seeing electron shells. Then the exceptions start, and you have to explain them with evidence.

Difficulty●●○ Medium
KitComputer only: database + spreadsheet
TimeAbout 10 hours
FitsHL (successive IEs and dips); SL: first IE trends
  • ✓ you like spotting patterns in data
  • ✓ you can build a spreadsheet
  • ✓ you want to explain a result, not just describe it

The big idea

← this is your RQ hook!

Take electrons off an atom one at a time and each costs more than the last, until you reach a new shell and the cost leaps. On a log scale those leaps are easy to see, and they match the shell model. Across a period the first ionisation energy rises with a couple of dips that a plain 'more protons' story misses. Don't only describe the dips. Link them to sub-levels and electron repulsion, and test that link with numbers from your own data. It is all database work, so your marks come from sampling, processing and explaining.

Make it yours: pick one twist

Copying a classic won't show your choices. Pick one of these (or invent your own) and your IA becomes yours.

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Successive energies for two or three elements

Plot log₁₀ of successive ionisation energies for elements from different groups.

→ Several curves on one graph. The first big jump should move with the number of valence electrons, which gives you a prediction to test.
First ionisation energy across a period

Plot first ionisation energy against atomic number for period 2 or period 3.

→ A different graph type. The dips become the focus, and you must explain each one with evidence rather than just spot it.
Estimate the effective nuclear charge

Use the hydrogen-like relation IE = 13.6 Z²/n² (in eV; not in the course, so introduce it yourself) to turn each value into an effective Z.

→ Adds a calculation and a model to evaluate. It is exact only for one-electron species, which gives you something real to discuss.
Go down a group

Compare first ionisation energies down group 1 or group 17.

→ Tests distance and shielding rather than sub-levels, so your explanation uses a different part of the model.
Compare two databases

Take the same values from two sources and compare them.

→ Database values come without error bars. The disagreement between sources gives you a genuine uncertainty to work with.

Your Chemistry IA research question: run the check

Write your own question first. Then make sure it ticks every box:

  • Names the element(s) and the exact quantity: first or successive ionisation energy, and in which unit.
  • Names the independent variable (electrons removed, or atomic number) and the dependent variable, with the range of values.
  • Says which single database supplies every value, so differences come from the chemistry and not from mixed sources.
  • Is specific about what you will explain (the jump, a dip, a trend), so the question can be answered and not just described.
  • Is narrow enough for about 10 hours: a few elements or one or two periods, not the whole periodic table.

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The set-up

There is no apparatus here: your set-up is the data pipeline. Draw yours with the real database name, your filter and the columns you calculate.

nIEIElogone source for everyvalue (and cite it!)add a log₁₀ column,same unit throughoutmark the jump andthe dips yourselfwrite down your filter ruleso someone could repeat itkJ per mol or eV?convert once, label it

How your Chemistry IA could be laid out

The usual order for a topic like this, what each part needs to show, and roughly how much of your 3,000 words it takes. The words are all yours.

Research question and context~250
Your question; why ionisation energies test the shell model; the pattern you predict and why.
Background chemistry~450
Definition of ionisation energy (with state symbols); shells, sub-levels, shielding and electron repulsion; what each should do to your plot. Cite your sources.
Variablestable
Independent, dependent and controlled variables. The control is the single source and the same units, so say how you enforced it.
Data source and sampling~400
Which database and why; which elements and why those; how you filtered; how you avoided choosing only the values that fit.
Safety, ethics, environment~50
No chemicals, so keep it short and honest. Mention the database terms of use and keeping your own copy of what you used.
Raw datatable
The values you extracted, with source, units and the precision the database gives.
Processing~250
Unit conversions and logarithms with one worked example each; how you treated the limited precision of the data.
Graphs and analysis~400
The graph you chose and why; the jump or dips marked; any calculation (such as effective charge) and what it shows.
Conclusion~450
Answer the question with values; say which part of the shell model your data support and which it does not fully explain.
Evaluation~650, the biggest part!
Limits of the data (rounding, one source, gas-phase values) and of the model; what you would add; how much each matters.
Referencesnot counted
The database (with date accessed) and every text you used.

What your Chemistry IA graph could look like

mark the jump ON the graph

Made-up numbers shaped like a real pattern, to show the form of a strong graph, not the answer. Your element and values will differ. example only

012345672.83.03.23.43.63.84.04.24.44.64.85.0Number of electrons removedlog₁₀(ionisation energy / kJ mol⁻¹)shell model: steps up to an inner shellsmooth trend if there were no shellsvalues from your databasethe big jump: now you areremoving an inner-shell electronILLUSTRATIVE · MADE-UP DATA
  • The unit sits inside the log: log₁₀(IE / kJ mol⁻¹). A log of a number with units means nothing.
  • A log scale because the leap to an inner shell would squash every other point on a linear axis.
  • No error bars here because the database gives none. Say how precise the values are, and compare two sources if you can.
  • Mark the jump on the graph itself and say how many electrons come before it.
  • Another graph to consider: first ionisation energy against atomic number across a period, with each dip labelled.

Your game plan

decide your filter rule BEFORE you look

Tick steps off as you go. We'll remember on this device.

0 of 10 done

  1. Read and predictRevise shells, sub-levels, shielding and electron repulsion. Before you open a database, write down what you expect the plot to look like, and where you expect breaks.
  2. Choose and test a sourcePick one database and check how it lists values, in which units, and how many figures. Find out whether values are for gaseous atoms or ions.
  3. Trial run (1 lesson)Pull the data for one element or one period into a spreadsheet and plot it. Is the pattern visible? Is anything missing or odd? Fix your plan now.
  4. Decide your sampleChoose the elements and the range, and write down why. Decide the filter rule before you see the full set, so you are not choosing the values that suit your story.
  5. Build the spreadsheetKeep the raw values on one sheet untouched, and do every calculation on another with labelled columns and units.
  6. Process and plotConvert units once, take logarithms where needed, and plot. Mark the jump and each dip on the graph.
  7. Explain with evidenceFor each deviation write the model's prediction first, then check it against a number: the size of the dip, a calculated effective charge, or a neighbouring element.
  8. EvaluateWhich limits matter most: rounding, a single source, gas-phase values, or the model itself? Rank them rather than listing them.
  9. Write, then cutWrite in the order of the layout. Tables, graphs, equations and references are not counted, so let them carry detail.
  10. Check before your teacher's draftRun the checklist below and get your RQ or draft checked. Your teacher reads one draft only.

Chemistry you'll need

Traps to avoid in this Chemistry IA

  • Describing the trend and stopping: a dip needs an explanation backed by a number, not just 'it is more stable'.
  • Explaining the N/O dip with 'half-filled shells are stable' alone. The stronger argument is repulsion between the paired electrons, and you can test it.
  • Mixing sources: if values for different elements come from different tables, differences may be the source and not the chemistry.
  • Units: eV in one column and kJ mol⁻¹ in another, or taking the log of a value that still has a unit attached.
  • Period mix-up: the Be/B and N/O dips are in period 2. The matching dips in period 3 are Mg/Al and P/S. Say which period you used.
  • An evaluation with no comment on the data themselves: their precision, how they were measured, and what the model leaves out.

More Chemistry IA ideas like this

Make sure it's yours

This guide shows how a topic like this is usually approached. It is not an IA. Your question, choices, data, analysis and words must be your own: change something, tell your teacher where the idea came from, and follow your school's rules on outside help.

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