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Even More on Periodic Trends. Chem 11. Ionization Energy. Ionization Energy. The amount of energy required to completely remove an electron from a gaseous atom. Removing one electron makes a +1 ion. The energy required to remove one e - is called the first ionization energy.

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Ionization energy
Ionization Energy

  • The amount of energy required to completely remove an electron from a gaseous atom.

  • Removing one electron makes a +1 ion.

  • The energy required to remove one e- is called the first ionization energy.

    X(g) + energy →X+ + e-

Ionization energy1
Ionization Energy

  • The second ionization energy is the energy required to remove another (the second electron).

  • 2E always greater than first IE.

  • The third IE is the energy required to remove a third electron.

  • 3E greater than 1st of 2nd IE.

X+ (g) + energy X2+ (g) + e-

X2+ (g) + energy X3+ (g) + e-

Chem 11

Ionization Energies (kJ/mol)

Symbol First Second Third

11749 14840 3569 4619 4577 5301 6045 6276

5247 7297 1757 2430 2352 2857 3391 3375 3963

1312 2731 520 900 800 1086 1402 1314 1681 2080


What determines ie
What determines IE?

  • The greater the effective nuclear charge the greater IE

  • The positive nuclear charge increases as you go L to R across each period, so it is more difficult to pull electrons from the atoms on the R side

  • Less distance from nucleus increases IE

  • Filled and half filled sublevels have lower energy, so removing them raises the IE.

Ie period trend
IE Period Trend

  • Ionization energy increases from left to right for each period


  •  From Na to Ar (11 protons to 18 protons), the nuclear charge in each element increases.

  •  The electrons are attracted more strongly to the nucleus – so it takes more energy to remove one from the atom.

Ie group trend
IE Group Trend

  • Ionization energy decreases down each group

    Ex: Going from Be to Mg, IE decreases because:

    • Mg outer electron is in the 3s sub-shell rather than the 2s (Be). This is higher in energy

    • The 3s electron is further from the nucleus and shielded by the inner electrons

    • So the 3s electron is more easily removed

Driving force for ie
Driving Force for IE

  • Full Energy Levels are very low energy.

  • Noble Gases have full energy levels.

  • Atoms behave in ways to achieve noble gas configuration.

2 nd ionization energy
2nd Ionization Energy

  • Remember 2E is always higher then 1E

  • For elements that reach a filled or half filled sublevel by removing 2 electrons 2nd IE is lower than expected.

  • Makes it easier to achieve a full outer shell

  • True for s2

  • Alkaline earth metals form +2 ions and have lower 2nd IEs

3 rd ie
3rd IE

  • Using the same logic s2p1atoms have an low 3rd IE.

  • Atoms in the aluminum family form +3 ions, so they have low 3rd IEs.

  • 2nd IE and 3rd IE are always higher than 1st IE!!!

Electron affinity
Electron Affinity

  • Is the energy given off when an atom gains an electron

  • Easiest to add to group 17 (7A) )most negative

  • Gets them to full energy level becomes stable – releases a large amount of energy.

  • Period Trend: increases (from positive to very negative) from left to right atoms (metals are losers so to gain an electron will only bring about a small increase in stability (if any) – small energy change)

Electron affinity1
Electron Affinity

  • The energy change associated with adding an electron to a gaseous atom.

  • Easiest to add to group 7A, so energy change will be negative, energy is released.

  • Increase (from positive to negative) from left to right atoms become smaller, with greater nuclear charge