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Ionization Energy

Ionization energy (IE): The energy required

to remove an electron from a gaseous atom orion, where the atom or ion is assumed to be in

its ground state. (p91, 3, 5)

X(g)X+(g) + e

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First IE of Aluminum

Al(g)Al+(g) + e

I1 = 580 kJ/mol

The first ionization energyI1 is the energy

required to remove the highest energy

electron (the one bound least tightly) of an

atom. (p91, r3)

I1: Remove a 3p electron. (Al: [Ne] 3s2

3p1)

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2nd and 3rd IEs of Aluminum

Al+(g)Al

2+(g) + e

I2 = 1815 kJ/mol

Al2+(g)Al3+(g) + e

I3 = 2740 kJ/mol

I1

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Fourth IE of Aluminum

Al2+

(g)Al3+

(g) + e

I3 = 2740 kJ/mol

Al3+(g)Al4+(g) + e

I4 = 11,600 kJ/mol

The largest jump in ionization energy by far

occurs in going from the third ionizationenergy (I3) to the fourth (I4). (pp91-92)

I3: Remove a 3s electron. (Al2+

: [Ne] 3s1)

I4: Remove a 2p (core) electron. (Al3+

: [Ne])

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IEs for the 3rd-Period Elements

p92, Table 2.5

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First IEs for the Elements

in the First Six Periods

p92, Figure 2.32

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Periodic Trends in 1st-Ionization Energy

In general as we go across a periodfrom left

to right, the first ionization energy increases.(p92, r3)

Electrons added in the same principal

quantum level do not completely shield theincreasing nuclear charge caused by the

added protons. (p92, r3)

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Shielding Effect

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s >p > d>f

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Zeff

Zeff= Z

Zeff

Z

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Poor Shielding Effect for the Same Level

Electrons in the same principal quantum level

are generally more strongly bound as wemove to the right on the periodic table, and

there is a general increase in ionization

energy values as electrons are added to agiven principal quantum level. (p92, r3)

Zeff: small (left)large (right)

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IEs for 1A and 8A Elements

p92, Table 2.6

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1st-IE for the Same Group

First ionization energy decreases in going

down a group. (p92, r2)

The electrons being removed are, on average,

farther from the nucleus.

As n increases, the size of the orbital

increases, and the electron is easier to remove.

(p92, r2)