12.1.1 Evidence of energy levels from 1st I.E. trends across a period IB chemistry HL
12.1.1 Explain how evidence from first ionization energies across periods accounts for the existence of main energy levels and sub-levels in atoms. As nuclear charge increase, electrons require more energy to remove (in the same period). Sub energy levels can be seen in the data. The IB loves to ask about why "Sulphur" does not fit the pattern. This is because removing the 3p electron leaves a stable configuration so this requires less energy than predicted OR you can say that the electron pair in the 3p repel , making the energy required to remove it lower than the pattern would suggest. YAWN!
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