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Ionisation Enthalpy or Ionisation Potential - (Concept)
Ionisation Enthalpy
Ionisation enthalpy may be defined as the minimum energy required to remove the most loosely bound electron from an isolated gaseous atom to convert it into a gaseous monovalent positive ion.
IE1 is ionisation enthalpy or also known as first ionisation enthalpy.
Ionisation Potential
Ionisation enthalpy is also expressed in terms of ionisation potential. It is the minimum potential difference required to remove the outermost electron from a gaseous atom to form a cation. As the ionisation energy increases, the ionisation potential also increases.
Factors Affecting Ionisation Enthalpy
The ionisation enthalpy of any atom is affected by the following factors.
-
Size of the atom: The larger the size of an atom, the lower is the ionisation enthalpy. As the atomic size increases, the distance between the outermost electrons and the nucleus increases due to which the force of attraction between the nucleus and these outermost electrons decreases, thus it becomes easy to remove an electron from the atom and hence the ionisation enthalpy decreases. Thus,
Ionisation enthalpy decreases as Atomic size increases
-
Screening effect: The higher is the value of the screening effect, the lower is the ionisation enthalpy. As the screening effect increases, the repulsion between the electrons increases, and thus the removal of an electron from the atom becomes easier. Thus,
Ionisation enthalpy decreases as the Screening effect increases
-
Nuclear charge: As the nuclear charge increases, the force of attraction between the nucleus and electrons also increases and thus the removal of electron from the atom becomes difficult and hence the ionisation enthalpy increases. Thus,
Ionisation enthalpy increases as Nuclear charge increases
-
Half filled and fully filled orbitals: The atoms with half-filled and fully filled orbitals are more stable than other atoms. Thus removing an electron from these atoms requires a little more energy. Thus for these atoms with half-filled and fully filled orbitals, the ionisation enthalpy is higher than others.
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The shape of orbital: The ionisation enthalpy also depends on the shape of the orbital in which the last electron enters. The more the orbital is close to the nucleus, the more energy is required to remove the electron in the same orbit. Thus, the ionisation enthalpy for the orbitals from the same orbit follows the given order:
s > p > d > f
Variation of Ionisation Enthalpy
-
In moving down the group, the ionisation enthalpy decreases. As we move down in the group, the number of shells increases due to which the force of attraction between the nucleus and the outer electrons decreases, thus removing an electron from the atom becomes easy and hence ionisation enthalpy decreases. There are some exceptions after the element with atomic number 72. The elements with atomic number from 73 to 82 have higher ionisation enthalpy than the earlier elements in their respective group. This deviation of behaviour is because of the lanthanide contraction.
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In moving from left to right in a period, the ionisation enthalpy increases. In period, the nuclear charge increases but the number of shells remain the same, thus the force of attraction between the nucleus and the outer electrons increases, and hence the ionisation enthalpy increases. In a period, some elements like Be, Mg, N, and P have exceptionally higher ionisation enthalpies than expected. This is because of their half-filled or fully filled outer orbitals configuration.
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For every element, the successive ionisation energy increases. This is because of the increase in the nuclear charge due to the successive removal of electrons.
Importance of Ionisation Enthalpy
Ionisation enthalpy is an important factor for determining the nature of an element. The elements with low ionisation enthalpies are metals while the elements with higher ionisation enthalpies are non-metals.
The stability of oxidation states of an element can also be determined on the basis of the value of ionisation enthalpies.
| Exam | Chapter |
| JEE MAIN | Classification of Elements and Periodic table |
The increasing order of the first ionisation enthalpies of the elements B, P, S and F (lowest first) is
| A. |
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| B. |
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| C. |
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| D. |
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The element having greatest difference between its first and second ionization energies, is :
| A. |
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| B. |
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| C. |
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| D. |
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In comparison to boron, beryllium has:
| A. |
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| B. |
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| C. |
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| D. |
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The formation of the oxide ion requires first an exothermic and then an endothermic step as shown below.
This is because
| A. |
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| B. |
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| C. |
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| D. |
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Which of the following element has the lowest ionisation potential?
| A. |
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| B. |
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| C. |
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| D. |
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Which of the following element has the lowest value of IE1?
| A. |
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| B. |
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| C. |
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| D. |
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In which of the following arrangements the order is NOT according to the property indicated against it?
| A. |
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| B. |
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| C. |
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| D. |
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In the plot of ionisation energy against atomic number. Maxima and Minima respectively occurs at
| A. |
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| B. |
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| C. |
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| D. |
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Which of the following represents the correct order of increasing first ionization enthalpy for Ca,Ba,S ,Se and Ar?
| A. |
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| B. |
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| C. |
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| D. |
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Which of the following has the lowest ionisation potential value?
| A. |
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| B. |
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| C. |
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| D. |
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Which one of these has lowest ionisation potential?
| A. |
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| B. |
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| C. |
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| D. |
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Which of the following is a stable ion?
| A. |
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| B. |
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| C. |
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| D. |
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Elements having low value of ionisation potential acts as
| A. |
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| B. |
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| C. |
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| D. |
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The first ionisation potentials of Na, Al & Mg are in the order
| A. |
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| B. |
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| C. |
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| D. |
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Which of the following oxidation states of Bi is most stable?
| A. |
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| B. |
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| C. |
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| D. |
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Which one of the following order shows the correct increasing order of basicity of alkali metal hydroxides?
| A. |
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| B. |
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| C. |
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| D. |
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Identify the correct statement among the following:
| A. |
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| B. |
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| C. |
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| D. |
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The third ionization enthalpy is minimum for:
| A. |
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| B. |
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| C. |
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| D. |
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The first ionization energy (in kJ\mol) of Na, Mg, Al and Si respectively, are:
| A. |
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| B. |
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| C. |
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| D. |
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B has smaller first ionization enthalpy than Be. Consider the following statements :
(I) It is easier to remove 2p electron than 2s electron.
(II) 2p electron of B is more shielded from the nucleus by the inner core of electrons than the 2s electrons of Be.
(III) 2s electron has more penetration power than 2p electron
(IV) atomic radius of B is more than Be
(atomic number B = 5, Be = 4)
The correct statements are :
| A. |
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| B. |
|
| C. |
|
| D. |
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The correct sequence of ionization potential is:
| A. |
|
| B. |
|
| C. |
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| D. |
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How does the ionisation potential vary with the increase in Zeff?
| A. |
|
| B. |
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| C. |
|
| D. |
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Consider the element Mg, Al, S, P and Si, the correct increasing order of their first ionization enthalpy is:
| A. |
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| B. |
|
| C. |
|
| D. |
|
Match List - I with List - II
List - I List - II
Electronic configuration of elements in kJ
(a) (i) 801
(b) (ii) 899
(c) (iii) 1314
(d) (iv) 1402
Choose the most appropriate answer from the options given below :
| A. |
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| B. |
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| C. |
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| D. |
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The incorrect statement among the following is
| A. |
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| B. |
|
| C. |
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| D. |
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The ionization energy of nitrogen is more than that of oxygen because
| A. |
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| B. |
|
| C. |
|
| D. |
|
Highest energy will be absorbed to eject out the electron in the configuration
| A. |
|
| B. |
|
| C. |
|
| D. |
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The screening effect of inner electrons of the nucleus causes
| A. |
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| B. |
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| C. |
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| D. |
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Amongst the elements with following electronic configurations, which one of them may have the highest ionization energy?
| A. |
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| B. |
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| C. |
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| D. |
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Identify the elements X and Y using the ionisation energy values given below:
\begin{array}{ccc}
& \text { Ionization energy } & (\mathbf{k J} / \mathbf{m o l}) \\
& 1^{\text {st }} & 2^{\text {nd }} \\
\mathrm{X} & 495 & 4563 \\
\mathrm{Y} & 731 & 1450
\end{array}
| A. |
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| B. |
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| C. |
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| D. |
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The first ionization energy of magnesium is smaller as compared to that of elements x and Y, but higher than that of Z. The elements X, Y, and Z respectively:
| A. |
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| B. |
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| C. |
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| D. |
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The five successive ionization enthalpies of an element are 800, 2427, 3658, 25024, and 32824 kJ/mol. The number of valence electrons in the element is :
| A. |
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| B. |
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| C. |
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| D. |
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Given below are two statements. One is labelled as Assertion A and the other is labelled as Reason R.
Assertion A: The first ionization enthalpy for oxygen is lower than that of nitrogen.
Reason R: The four electrons in 2p orbitals of oxygen experience more electron-electron repulsion.
In the light of the above statements, choose the correct answer from the options given below.
| A. |
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| B. |
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| C. |
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| D. |
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The incorrect statement is
| A. |
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| B. |
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| C. |
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| D. |
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Outermost electronic configurations of four elements A, B, C, D are given below :
(A)
(B)
(C)
(D)
The correct order of first ionization enthalpy for them is :
| A. |
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| B. |
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| C. |
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| D. |
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The correct decreasing order for metallic character is
| A. |
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| B. |
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| C. |
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| D. |
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The CORRECT order of first ionisation enthalpy is :
| A. |
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| B. |
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| C. |
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| D. |
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Which of the following statement is correct?
| A. |
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| B. |
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| C. |
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| D. |
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The element which has the highest ionization energy is
| A. |
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| B. |
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| C. |
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| D. |
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The correct order of the first ionization enthalpies is :
| A. |
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| B. |
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| C. |
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| D. |
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The first ionisation potential of Na is 5.1 eV .The value of electron gain enthalpy (in eV) of Na+ will be :
| A. |
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| B. |
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| C. |
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| D. |
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Which of the following explanations justifies for not placing hydrogen in either group of alkali metals or halogens?
| A. |
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| B. |
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| C. |
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| D. |
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The electronic configuration with the highest ionization enthalpy is :
| A. |
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| B. |
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| C. |
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| D. |
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Consider the following ionization enthalpies of two elements ‘A’ and ‘B’.
Which of the following statements is correct ?
| A. |
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| B. |
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| C. |
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| D. |
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Ionisation energy of is
atom -1 The energy of the first stationary state
of
is
| A. |
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| B. |
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| C. |
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| D. |
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Which of the following atoms has the highest first ionization energy ?
| A. |
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| B. |
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| C. |
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| D. |
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The ionization potential of N>O because :
| A. |
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| B. |
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| C. |
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| D. |
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As shielding effect increases down the group, the ionization potential value :
| A. |
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| B. |
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| C. |
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| D. |
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The ionization enthalpies of Na & K are 495KJ/mol & 419KJ/mol respectively. The energy required to convert all the atoms present in 23 mg of Na vapours & 39 mg of K vapours of their respective gaseous cations respectively are:
| A. |
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| B. |
|
| C. |
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| D. |
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It is most easier to remove the electron from :
| A. |
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| B. |
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| C. |
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| D. |
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Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A) : The first ionization enthalpy of 3 d series elements is more than that of group 2 metals
Reason (R) : In 3d series of elements successive filling of d-orbitals takes place.
In the light of the above statements, choose the correct answer from the options given below :
| A. |
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| B. |
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| C. |
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| D. |
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The standard electrode potential of M+ /M in aqueous solution does not depend on
| A. |
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| B. |
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| C. |
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| D. |
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For elements and
, the correct order of first ionization enthalpy is:
| A. |
|
| B. |
|
| C. |
|
| D. |
|
Find out a number of pairs in which 1st species have lower Ionisation energy than the second species.
(a) $\mathrm{Na} \;\&\; \mathrm{Na}^{+}$
(b) $\mathrm{Be}\; \& \mathrm{~B}$
(c) $\mathrm{N}\; \& \mathrm{O}$
(d) $O\; \& \;\mathrm{Ne}$
(e) $B\; \&\; C$
| A. |
|
| B. |
|
| C. |
|
| D. |
|
Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R :
Assertion A : The first ionisation enthalpy decreases across a period.
Reason R : The increasing nuclear charge outweighs the shielding across the period.
In the light of the above statements, choose the most appropriate from the options given below :
| A. |
|
| B. |
|
| C. |
|
| D. |
|
The element having the highest first ionization enthalpy is
| A. |
|
| B. |
|
| C. |
|
| D. |
|
The transition metal having highest 3rd ionization enthalpy is :
| A. |
|
| B. |
|
| C. |
|
| D. |
|
The correct order of the first ionization enthalpy is
| A. |
|
| B. |
|
| C. |
|
| D. |
|
If the penetration effect is high in any element then the ionisation potential
| A. |
|
| B. |
|
| C. |
|
| D. |
|
Which electronic configuration has the lowest ionisation energy?
| A. |
|
| B. |
|
| C. |
|
| D. |
|
First ionization enthalpy of group 13, the order is
| A. |
|
| B. |
|
| C. |
|
| D. |
|
Among $C e\left(4 f^1 5 d^1 6 s^2\right), N d\left(4 f^4 6 s^2\right), E u\left(4 f^7 6 s^2\right)$ and $D y\left(4 f^{10} 6 s^2\right)$, the elements having highest and lowest $3^{\text {rd }}$ ionization energies, respectively, are
| A. |
|
| B. |
|
| C. |
|
| D. |
|
The first ionisation energy of Na, B, N and O atoms follow the order:
| A. |
|
| B. |
|
| C. |
|
| D. |
|
The first ionization enthalpies for three elements are 1314, 1680 and 2080 kJ mol-1, respectively. The correct sequence of the elements is:
| A. |
|
| B. |
|
| C. |
|
| D. |
|
The first ionization potential (IP) of the elements $N a, M g, S i, P, C l$ and $A r$ are $5.14,7.65,8.15,10.49,12.97$ and 15.76 eV , respectively. The IP (in eV ) of K is closest to:
| A. |
|
| B. |
|
| C. |
|
| D. |
|
Match List -I with List-II
| List-I | List-II | ||
| (A) | $\mathrm{Al}^{3+}<\mathrm{Mg}^{2+}<\mathrm{Na}^{+}<\mathrm{F}^{-}$ | (I) | Ionisation Enthalpy |
| (B) | $\mathrm{B}<\mathrm{C}<\mathrm{O}<\mathrm{N}$ | (II) | Metallic character |
| (C) | $\mathrm{B}<\mathrm{Al}<\mathrm{Mg}<\mathrm{K}$ | (III) | Electronegativity |
| (D) | $\mathrm{Si}<\mathrm{P}<\mathrm{S}<\mathrm{Cl}$ | (IV) | Ionic radii |
Choose the correct answer from the options given below :
| A. |
|
| B. |
|
| C. |
|
| D. |
|
Given below are two statements :
Statement (I) : The first ionization energy of Pb is greater than that of Sn
Statement(II) : The first ionization energy of Ge is greater than that of Si .
In the light of the above statements, choose the correct answer from the options given below:
| A. |
|
| B. |
|
| C. |
|
| D. |
|
The successive 5 ionisation energies of an element are $800,2427,3658,25024$ and $32824 \mathrm{~kJ} / \mathrm{mol}$, respectively. By using the above values predict the group in which the above element is present:
| A. |
|
| B. |
|
| C. |
|
| D. |
|
Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R
Assertion (A) : The energy required to form Mg2+ from Mg is much higher than that required to produce Mg+
Reason (R): Mg2+ is small ion and carry more charge than Mg+.
In the light of the above statements, choose the correct answer from the options given below.
| A. |
|
| B. |
|
| C. |
|
| D. |
|
Amongst the following elements whose electronic configurations are given below, the one having the highest ionization enthalpy is
| A. |
|
| B. |
|
| C. |
|
| D. |
|
In which of the following options order of arrangement does not agree with the variation of property indicated against it?
(i) Al3+< Mg2+< Na+ < F– (increasing ionic size)
(ii) B < C < N < O (increasing first ionisation enthalpy)
(iii) I < Br < Cl < F (increasing electron gain enthalpy)
(iv) Li < Na < K < Rb (increasing metallic radius)
| A. |
|
| B. |
|
| C. |
|
| D. |
|
The first ionisation enthalpies of Na, Mg, Al and Si are in the order:
| A. |
|
| B. |
|
| C. |
|
| D. |
|
The order of decreasing ionisation enthalpy in alkali metals is
| A. |
|
| B. |
|
| C. |
|
| D. |
|
For gaseous reaction
$
\mathrm{K}+\mathrm{F} \rightarrow \mathrm{~K}^{+}+\mathrm{F}^{-}, \Delta \mathrm{H}=19 \mathrm{kcal} \mathrm{~mol}^{-1}
$
The $I E_1$ of $K$ is 4.3 eV .
Then calculate $\Delta_{\mathrm{eg}} \mathrm{H}^{-}$of F .
| A. |
|
| B. |
|
| C. |
|
| D. |
|
The ionisation energy of H atom is 13.6 eV. What will be the ionization energy of $\mathrm{He}^{+}$and $\mathrm{Li}^{2+}$ions respectively ____eV, ____eV
| A. |
|
| B. |
|
| C. |
|
| D. |
|
Which of the following statements are correct?
A. The process of the addition an electron to a neutral gaseous atom is always exothermic
B. The process of removing an electron from an isolated gaseous atom is always endothermic
C. The $1^{\text {st }}$ ionization energy of the boron is less than that of the beryllium
D. The electronegativity of C is 2.5 in $\mathrm{CH}_4$ and $\mathrm{CCl}_4$
E. Li is the most electropositive among elements of group I
Choose the correct answer from the options gives below
| A. |
|
| B. |
|
| C. |
|
| D. |
|
Given below are two statements :
Statement (I) : The first ionisation enthalpy of group 14 elements is higher than the corresponding elements of group 13.
Statement (II) : Melting points and boiling points of group 13 elements are in general much higher than those the corresponding elements of group 14.
In the light of the above statements, choose the most appropriate answer from the options given below :
| A. |
|
| B. |
|
| C. |
|
| D. |
|
The atomic number of the element from the following with lowest $1^{\text {st }}$ ionisation enthalpy is :
| A. |
|
| B. |
|
| C. |
|
| D. |
|
A quantitative measure of the tendency of an element to lose electron is given by its Ionization Enthalpy.
