Ionization energy, 9(3)
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It is a measures the energy change that occurs when an electron is accepted by atom in the gaseous state.
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Ionization energy, 9(3)
- 1. Ionization Energy and Electron Affinity Dr. K. Shahzad Baig Memorial University of Newfoundland (MUN) Canada Petrucci, et al. 2011. General Chemistry: Principles and Modern Applications. Pearson Canada Inc., Toronto, Ontario. Tro, N.J. 2010. Principles of Chemistry. : a molecular approach. Pearson Education, Inc.
- 2. Ionization Energy Mg(g) → Mg+(g) + e- I1 = 738 kJ Mg+(g) → Mg2+(g) + e- I2 = 1451 kJ I1 = RH n2 Zeff1 2 I2 = RH n2 Zeff2 2 It is the quantity of energy a gaseous atom must absorb to be able to expel an electron. Ioniziation energy is the minimum energy required to remove an electron from the ground state of the isolated gaseous atom.
- 3. First Ionization Energy Ionization energies decrease as atomic radii increase. Coulomb s law the force of attraction between oppositely charged particles is directly proportional to the magnitudes of the charges
- 4. First Ionization Energy, I1 Increase Increase ionization energies decrease as atomic radii increase reflects the effect of n and on the ionization energy 𝐼 = 𝑅 𝐻 𝑥 𝑍 𝑒𝑓𝑓 2 𝑛2
- 5. I1 (P) vs. I1 (S)I1 (Mg) vs. I1 (Al)I2 (Mg) vs. I3 (Mg)
- 6. The more energy is required to strip an electron from the lower energy 3s orbital in Mg ([Ne] 3S2) than from a half-filled 3p orbital in Al([Ne] 3s2 3p1). I2 for S is slightly lower than for P for a different reason. Although the orbitals in the subshell ‘3p’ are degenerate, we can think of repulsion between electrons in the filled ‘3p’ orbital of a S atom ([Ne] 3s2 3p4) as making it easier to remove one of those electrons than an electron from the half-filled ‘3p’ subshell of a P atom ([Ne] 3s2 3p3) Consider the orbital diagrams for Mg, Al, P, and S shown in the margin. It is expected ‘l1’ of Al to be larger than for Mg. The reversal occurs because of the particular electrons lost. Mg loses a 3s electron, while Al loses a 3p electron.
- 7. Electron Affinity F(1s22s22p5) + e- → F- (1s22s22p6) Li(g) + e- → Li- (g) EA = -59.6 kJ Measures the energy change (attraction or affinity) that occurs when an electron is accepted by atom in the gaseous state. We assign a (-) value to the electron affinity when energy is released. The more (-) the EA, the greater the tendency the atom can accept an e- F(g) + e- → F-(g) EA = -328 kJ energy is given off
- 8. First Electron Affinities The smaller atoms to the right of the periodic table (for example, group 17) tend to have large, negative electron affinities. Electron affinities tend to become less negative in progressing toward the bottom of a group, with the notable exception of the second-period of groups 15, 16, and 17 (namely, N, O, and F). It is likely that for these small atoms, an incoming electron encounters strong repulsive forces from other electrons in the atom and is thereby not as tightly bound as we might otherwise expect .
- 9. Second Electron Affinities O(g) + e- → O-(g) EA = -141 kJ O-(g) + e- → O2-(g) EA = +744 kJ In considering the gain of a second electron by a nonmetal atom, we encounter positive electron affinities For an element like oxygen, the first electron affinity is negative and the second is positive. The high positive value of EA2 makes the formation of gaseous O2- seem very unlikely. The ion O2- can exist, however, in ionic compounds, such as MgO(s),
Editor's Notes
- Ionization energy is the quantity of energy a gaseous atom must absorb so that an electron is removed from it. The electron lost is the one most loosely held.
- Noble gases are the most difficult to ionize. Alkali metals are the easiest to ionize. Other trends are apparent and can be discussed better using specific examples (next slide) Coulomb's law states that: The magnitude of the electrostatic force of attraction or repulsion between two point charges is directly proportional to the product of the magnitudes of charges and inversely proportional to the square of the distance between them.
- Radii increase down a group. Radii decrease across a period in the main group (Zeff increases across main group elements). Radii in Transition metals remain fairly constant except for a few spikes. Electrons go into an inner shell, thus participate in shielding the outer shell electrons from the increasing Zeff. Equation …..As Zeff increases and the valence-shell principal quantum number n remains constant, the ionization energy should increase. And down a group, as n increases and increases only slightly, the ionization energy should decrease
- The trend in moving across a period (follow the colored stripe) is that atomic radii decrease, ionization energies increase, and the elements become less metallic, The zigzag diagonal line, Consider magnesium as an example. To remove a third electron, as measured by requires breaking into the especially stable noble-gas inner-shell electron configuration I3---is much larger than I2 so much larger that Mg3+ cannot be produced in ordinary chemical processes. Similarly, we do not encounter the ions Na2+ or Al4+ in chemical processes Removing the third electron from Mg causes a large jump in I.
- I2 of Al less than Mg because s- electron is removed from Mg and p-electron is removed from Al. I1 of S is less than that of P. This is due to e--e- repulsion of the fourth electron.
- Electron affinity, EA, can be defined as the enthalpy change, ∆H ea/ ,that occurs when an atom in the gas phase gains an electron.
- Gaseous O2- is not likely. It is OK in Na2O because of the energetically favorable electrostatic interactions. Here the electron to be added is approaching not a neutral atom, but a negative ion. There is a strong repulsive force between the electron and the ion, and the energy of the system increases