Calculate the first ionization energy of Lithium _____ KJmol | TestHub

Passage / Comprehension

There are two attractive features about relating chemical reactivity trends to ionization energies.

i) they can be measured with fair accuracy.

ii) They can be calculated from effective nuclear charge Z* such as developed from

Slater’s rule states that the basic equation for the energy of the $n$ th electron in an atom or ion is derived from:

The $R_{H}$ value in this equation is $1312.0 k J / m o l$ . Technically, to obtain ionization energy, it is necessary to apply the above equation to each electron in the atom being ionized and then to each electron in the ion produced, and subsequently take the difference.

In practice, $Z^{*}$ values are the same in the atom and the ion for electrons deep enough in the core, which simplifies the calculation somewhat.

Calculate the first ionization energy of Lithium _____ KJmol

Answer:

554

Solution:

The electron configuration of Li is $1 s^{2} 2 s^{1}$ . ×

The electron configuration of Li⁺ is $1 s^{2}$ .

Screening constant on 2s¹ electron is 2 ×0.85 = 1.7

Effective Nuclear charge =3.0 - 1.7 = 13

the Z* value of each 1s electron either in Li or in Li⁺is 3 - 0.35 =+2.65

Since it does not change upon ionization it makes no contribution to the

ionisation energy which is therfore equal to

$1312 (\frac{1.30}{2})^{2} = 554 k J m o l$

Chemistry - PERIODIC TABLE Question with Solution | TestHub

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