Chem 11
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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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Chem 11

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Chem 11

Even More on Periodic Trends

Chem 11


Chem 11

Ionization Energy


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)

SymbolFirstSecond 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

HHeLiBeBCNO F Ne


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

    Why?

  •  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!!!


Chem 11

Electron Affinity


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


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