Define ionization enthalpy. Discuss the factors affecting ionisation enthalpy of the elements and its trends in the periodic table.
Ionisation enthalpy: It is defined as the minimum amount of energy required to remove the most loosely bound electron from an isolated gaseous atom.
M(g) →M+(g) + e–I1 = First ionisation enthalpy
Similarly, second and third electrons are also removed by providing successive ionisation enthalpies.
Factors on which Ionisation Enthalpy Depends:
(i) Size of the atom: The larger the atomic size, smaller is the value of ionisation enthalpy. In a larger atom, the outer electrons are far away from the nucleus and thus force of attraction with which they are attracted by the nucleus is less and hence can be easily removed.
Ionisation enthalpy ∠1/ Atomic size
(ii) Screening effect: Higher the screening effect, the lesser is the value of ionisation enthalpy as the screening effect reduces the force of attraction towards nucleus and hence the outer electrons can be easily removed.
Ionisation enthalpy ∠1/ Screening effect
(iii) Nuclear charge: As the nuclear charge increases among atoms having same number of energy shells, the ionisation enthalpy increases because the force of attraction towards nucleus increases.
Ionisation enthalpy ∠Nuclear charge
(iv) Half filled and fully filled orbitals: The atoms having half filled and fully filled orbitals are comparatively more stable, hence more energy is required to remove the electron from such atoms. The ionization enthalpy is rather higher than the expected value in case of such an atom.
Ionisation enthalpy ∠Stable electronic configuration
(v) Shape of orbital: The s-orbital is more close to nucleus than the p-orbital of the same orbit. Thus, it is easier to remove electron from a p-orbital in comparison to s-orbital. In general, the ionisation enthalpy follows the following order
(s>p> d>f) orbitals of the same orbit.
Variation of ionisation enthalpy in the periodic table
ln general, the ionisation energy decreases down the group due to increase in atomic size. On the other hand, the ionisation energy increases across the period from left to right, again due to decrease in atomic size from left to right.
Give reasons:
(i) IE1 of sodium is lower than that of magnesium whereas IE2 of sodium is higher than that of magnesium.
(ii) Noble gases have positive value of electron gain enthalpy.
All transition elements are d-block elements, but all d-block elements are not transition elements. Explain.
Discuss and compare the trend in ionization enthalpy of the elements of group 1 with those of group 17 elements.
p-Block elements form acidic, basic and amphoteric oxides. Explain each property by giving two examples and also write the reactions of these oxides with water.
On the basis of quantum numbers, justify that the sixth period of the periodic table should have 32 elements.
How would you react to the statement that the electronegativity ofN on Pauling scale is 3.0 in all the nitrogen compounds?
Use periodic table to answer the following questions:
(a) Identify the element with five electrons in the outer subshell.
(b) Identify the element that would tend to lose two electrons.
(c) Identify the element that would tend to gain two electrons.
Which of the following have no unit?
(a) Electronegativity (b) Electron gain enthalpy
(c) Ionisation enthalpy (d) Metallic character
The first ionization enthalpies of Na, Mg, A1 and Si are in the order
(a) Na < Mg > A1 < Si
(b) Na>Mg>Al>Si
(c) Na < Mg < A1 < Si
(d) Na > Mg > A1 < Si
Which of the above elements is likely to be:
(a) the least reactive element (b) the most reactive metal
(c) the most reactive non-metal (d) the least reactive non-metal
(e) the metal which can form a stable binary halide of the formula MX2(X = halogen)
(f) the metal which can form a predominantly stable covalent halide of the formula MX (X = halogen)?
Ionisation enthalpies of elements of second period are given below:
Ionisation enthalpy/kJ mol-1: 520, 899, 801, 1086, 1402, 1314, 1681, 2080. Match the correct enthalpy with the elements and complete the graph given in figure. Also write symbols of elements with their atomic number.
Would you expect the first ionization enthalpies of two isotopes of the same element to be the same or different? Justify your answer.
Assign the position of the element having outer electronic configuration,
(i) ns2 np4 for n = 3 (ii) (n – 1) d2 ns2 for n = 4 and (iii) (n – 2) f7 (n – 1) d1 ns2 for n = 6 in the periodic table?
Explain why chlorine can be converted into chloride ion more easily as compared to fluoride ion from fluorine ?
Electronic configurations of four elements A, B, C and D are given below:
(A) 1s2 2s12p6
(B) 1 s2 2s2 2p4
(C) 1s2 2s2 2p6 3s1
(D) Is2 2s2 2p5
Which of the following is the correct order of increasing tendency to gain electron?
(a) A < C < B < D
(b) A < B < C < D
(c) D < B < C < A
(d) D < A< B < C
Which of the following elements can show covalency greater than 4?
(a) Be (b) P (c) S (d) B
Which of the following sets contain only isoelectronic ions?
(a) Zn2+, Ca2+, Ga3+, Al3+
(b) K+, Ca2+, Sc3+, Cl–
(c) P3-, S2- Cl–,K+
(d) Ti4+, Ar, Cl3+, V5+
In what manner is the long form of periodic table better than Mendeleev's
periodic table? Explain with examples.
Which important property did Mendeleev use to classify the elements in this periodic table and did he stick to that?
Which element do you think would have been named by
(i)Lawrence Berkeley Laboratory
(ii)Seaborg’s group?
The first ionisation enthalpy of magnesium is higher than that of sodium. On the other hand, the second ionisation enthalpy of sodium is very much higher than that of magnesium. Explain.
Those elements impart colour to the flame on heating in it, the atoms of which require low energy for the ionization (i.e., absorb energy in the visible region of spectrum). The elements of which of the following groups will impart colour to the flame?
(a) 2 (b) 13 (c) 1 (d) 17
In which of the following options order of arrangement does not agree with the variation of property indicated against it?
(a) Al3+ < Mg2+ < Na+ < F– (increasing ionic size)
(b) B < C < N < O (increasing first ionization enthalpy)
(c) I < Br < Cl < F (increasing electron gain enthalpy)
(d) Li < Na < K < Rb (increasing metallic radius)
Nitrogen has positive electron gain enthalpy whereas oxygen has negative. However, oxygen has lower ionization enthalpy than nitrogen explain.
Write down the outermost electronic configuration of alkali metals. How will you justify their placement in group 1 of the periodic table?
Consider the following species:
N3-, O2-, F–, Na+, Mg2+, Al3+
(a) What is common in them?
(b) Arrange them in order of increasing ionic radii?
Would you expect the second electron gain enthalpy of O as positive, more negative or less negative than the first? Justify your answer.
What is basic difference between the terms electron gain enthalpy and electro negativity?
Show by a chemical reaction with water that Na20 is a basic oxide and Cl207 is an acidic oxide.
What do you understand by ‘Representative elements’? Name the groups whose elements are called representative elements.
Elements A, B, C and D Iwoe atomic numbers 12,19, 29, and 36 respectively. On the basis of electronic configuration, write to which group of the periodic table each element belongs.
Which of the following sequences contain atomic numbers of only representative elements?
(a) 3, 33, 53, 87
(b) 2, 10, 22, 36
(c) 7, 17,25,37,48
(d) 9,35,51,88
Among the elements B, Al, C and Si,
(a) which element has the highest first ionization enthalpy
(b) which element has the most metallic character?
Justify your answer in each case.
Match the correct atomic radius with the element.
| Column I (Element) | Column II (Atomic radius (pm) |
| Be | 74 |
| C | 88 |
| 0 | 111 |
| B | 77 |
| N | 66 |
How would you explain the fact that the first ionization enthalpy of sodium is lower than that of magnesium but its second ionization enthalpy is higher than that of magnesium?
In the modem periodic table, the period indicates the value of
(a)atomic number (b) mass number (c) principal quantum number (d) azimuthal quantum number?
