question archive Hydrogen has only one proton, but its Ionization energy is much greater than that of Lithium, which has three protons
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Hydrogen has only one proton, but its Ionization energy is much greater than that of Lithium, which has three protons. Explain.
Answer:
Ionization Energy depends upon two factors- Atomic Size & Effective Nuclear Charge.
Effective Nuclear Charge is the charge experienced by a particular electron within the atom. It is the difference between the total charge in the nucleus and the number of shielded electrons.
The larger is the size of an atom, the farther is the electron from nucleus, loosely held is the electron by effective nuclear charge (as per Coulomb's law) and therefore the lesser energy we'll have to impart to the electron to knock it out.
The Larger is the effective nuclear charge, strongly held is electron by effective nuclear charge (as per Coulomb's law) and therefore larger energy we'll have to impart to the electron to knock it out.
The Electronic Configuration of Li & H are:
Li(3) : 1s^2 2s^1
H(1) : 1s^1
In Lithium, there are two core electrons, [1s^2], which are shielding the nuclear charge. Therefore effective nuclear charge in this case becomes (nuclear charge - absolute value of charge of core electron) that is Z-core electrons = 3 protons at nucleus - 2 core electrons in 1s^2 = 1 proton
In Hydrogen, the effective nuclear charge is also of 1 proton, as there are no core electrons.
However, the distance of electron in 2s^1 orbital from the nucleus in Lithium is larger than that of 1s^1 electron in Hydrogen. (Please note that the size of Lithium is about three times that of Hydrogen).
As effective nuclear charges (equals to that of 1 proton) in two cases remain the same but the size of Li is bigger than that of H. Therefore, 1st Ionization Energy of H is larger than that of Li.
Reference:
https://www.quora.com/Hydrogen-has-only-one-proton-but-its-ionization-energy-is-much-greater-than-that-of-lithium-which-has-three-protons-How-do-I-justify-this
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