Ionization energy Definition and 93 Threads

In physics and chemistry, ionization energy (American English spelling) or ionisation energy (British English spelling) is the minimum amount of energy required to remove the most loosely bound electron of an isolated neutral gaseous atom or molecule. It is quantitatively expressed as

X(g) + energy ⟶ X+(g) + e−where X is any atom or molecule, X+ is the resultant ion when the original atom was stripped of a single electron, and e− is the removed electron. This is generally an endothermic process. As a rule, the closer the outermost electrons are to the nucleus of the atom, the higher the atom's ionization energy.
The sciences of physics and chemistry use different units for ionization energy. In physics, the unit is the amount of energy required to remove a single electron from a single atom or molecule, expressed as electronvolts. In chemistry, the unit is the amount of energy required for all of the atoms in a mole of substance to lose one electron each: molar ionization energy or approximately enthalpy, expressed as kilojoules per mole (kJ/mol) or kilocalories per mole (kcal/mol).Comparison of ionization energies of atoms in the periodic table reveals two periodic trends which follow the rules of Coulombic attraction:
Ionization energy generally increases from left to right within a given period (that is, row).
Ionization energy generally decreases from top to bottom in a given group (that is, column).The latter trend results from the outer electron shell being progressively farther from the nucleus, with the addition of one inner shell per row as one moves down the column.
The nth ionization energy refers to the amount of energy required to remove an electron from the species having a charge of (n-1). For example, the first three ionization energies are defined as follows:

1st ionization energy is the energy that enables the reaction X ⟶ X+ + e−2nd ionization energy is the energy that enables the reaction X+ ⟶ X2+ + e−3rd ionization energy is the energy that enables the reaction X2+ ⟶ X3+ + e−The term ionization potential is an older and obsolete term for ionization energy, because the oldest method of measuring ionization energy was based on ionizing a sample and accelerating the electron removed using an electrostatic potential.
The most notable factors affecting the ionization energy include:

Electron configuration: this accounts for most element's IE, as all of their chemical and physical characteristics can be ascertained just by determining their respective electron configuration.
Nuclear charge: if the nuclear charge (atomic number) is greater, the electrons are held more tightly by the nucleus and hence the ionization energy will be greater.
Number of electron shells: if the size of the atom is greater due to the presence of more shells, the electrons are held less tightly by the nucleus and the ionization energy will be lesser.
Effective nuclear charge (Zeff): if the magnitude of electron shielding and penetration are greater, the electrons are held less tightly by the nucleus, the Zeff of the electron and the ionization energy is lesser.
Type of orbital ionized: an atom having a more stable electronic configuration has less tendency to lose electrons and consequently has higher ionization energy.
Electron occupancy: if the highest occupied orbital is doubly occupied, then it is easier to remove an electron.Other minor factors include:

Relativistic effects: heavier elements (especially those whose atomic number is greater than 70) are affected by these as their electrons are approaching the speed of light, and hence have a smaller atomic radius/higher IE.
Lanthanide and actinide contraction (and scandide contraction): the unprecedented shrinking of the elements affect the ionization energy, as the net charge of the nucleus is more strongly felt.
Electron pair energies and exchange energy: these would only account for fully filled and half-filled orbitals. A common misconception is that "symmetry" plays a part; albeit, none so far has concluded its evidence.

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  1. patric44

    An experiment for the determination of hydrogen ionization energy

    hi guys i saw this experiment in an old book that uses the gas vacuum tube "thyratron" for determining the hydrogen ionization energy , the idea i guess is straight forward : we set the filament current to a specific value then the electrons starts to emit from the cathode traveling its way to...
  2. I

    Why Does Ionization Energy Increase Differently Between Orbital Types?

    There is a large increase in ionization energy when an electron is removed from a p orbital versus when it is removed from a s orbital (and likewise when it is removed from the valence shell and from the inner shells). Why is there a smaller increase when successive electrons are removed from...
  3. jjson775

    Ionization Energy: Solving for n and Why I Was Wrong

    I got the right answers but have 2 questions. My first attempt was to use Equation 2 and solve for r then use Equation 3 and solve for n. My reasoning was that the photon needed to overcome the potential energy of the atom to release the electron. This gave me n =3.44. Why was I wrong? Then...
  4. S

    I Breaking an atom down in it's components.

    Good day, I have a question about breaking an atom down in it's components. For an example we have a neutral 4-helium atom. The helium atom have a nucleus which contains 2 protons and 2 neutrons. Around the nucleus of the helium atom 2 electron orbits in the k-shell (according to Bohr's...
  5. I

    First ionization energy of group 1 and group 2 elements

    The first ionization energy decreases between group 5 and group 6 due to the repulsion between the electrons in the p orbital. Although I understand that the effective nuclear charge increases between group 1 and group 2 elements, why isn't this the case between group 1 and group 2 elements...
  6. ilovepudding

    B Ionization energy and energy levels

    Hi, The ionization energy is defined as the minimum amount of energy required to remove the most loosely bound electron, the valence electron, of an isolated neutral gaseous atom. Our physics teacher also told us while explaining this concept in the context of energy levels, that it is equal...
  7. S

    X-ray production and ionization energy

    I am confused with the Kvp and Kep. I know that In the x-ray tube, after heating the filament and the electron cloud if formed, then the step-up transformer is going to increase the voltage and reduce the current to produce a high potential difference to that electrons will accelerate from the...
  8. patric44

    Chemistry Why does this equation not give me the ionization energy of lithium?

    i am trying to calculate the first ionization energy for lithium with this equation but it seems to work only with hydrogen ? i put nf = infinity and ni =2 ,and z = 3 for lithium and it gives about 30 ev not 5.39172 ev which is the value for lithium : i will appreciate any help in this
  9. C

    I Confusion on binding energy and ionization energy.

    1) I know that the binding energy is the energy that holds a nucleus together ( which equals to the mass defect E = mc2 ). But what does it mean when we are talking about binding energy of an electron ( eg. binding energy = -Z2R/n2 ? ). Some website saying that " binding energy = - ionization...
  10. John Greger

    What Is the Correct Method to Estimate Ionization Energy in He-like Carbon?

    Homework Statement In He-like Carbon, C V, the excitation energy of 1s3s ##^1S## is 2851180 ##cm^-1## and for 1s4s ##^1S## it is 2988246 ##cm^-1##. Estimate the ionization energy. Compare with the value in the NIST database! Homework Equations ##E_{io}= T + E_{excitation}, ## ##T =...
  11. Andrew Church

    I Composition of the Sun: How We Know via Spectral Absorption Lines

    The question “how do we know the composition of the sun” falls shorts everywhere I look. 1. There is the spectral absorption lines. Explanations given how that works, indicate how we know the elements, but fails to tell us how we know about the preponderance of Hydrogen and Helium...
  12. neilparker62

    Measure ionization energy (Hydrogen/Deuterium)

    Just wondering if there's any accurate method for direct measurement of the ionization energy of atomic Hydrogen and/or Deuterium ? There's lots of measurements on transitions between various hydrogen/deuterium energy levels but not (it seems) to the limit where n = infinity. Alternatively...
  13. Pushoam

    Energy needed to remove both electrons from a He atom

    Homework Statement Homework EquationsThe Attempt at a Solution [/B] Both electrons are in 1s orbit. For taking out the second electron, I will have to put slightly more energy than 24.6eV. So, the energy required to remove both electrons should be slightly more than 49.2 eV. So, I...
  14. B

    Determining ionization energy of Lithium.

    Homework Statement What is the third ionization energy of Li in its ground state? A. 4.91 E-18 J B. 6.54 E-18 J C. 7.79 E-18 J D. 9.20 E-18 J E. 1.96 E-17 J Homework Equations Maybe: EN=-(2.18E-18)(Z2/N2) The Attempt at a Solution Plugging in values doesn't give me any of the answers. At...
  15. L

    [College Chemistry] Electron Affinity and Ionization Energy

    Homework Statement Here's the pic of the problem and my work The Attempt at a Solution I'm not sure how I'm suppose to calculate the energy change? Did i do it correctly in the picture? For number 9, I just added IE1 and IE2 and subtracted EA1 to get a total of 3200.3. This means that the...
  16. A

    I Difference between binding energy and ionization energy

    Hi! I wonder since some time why ionization energies are not equal to binding energies. For instance, take the case of aluminum in the following configuration [Ne]3s²3p Ionization energy ~ 6 eV Binding energy ~ 5 eV Where does this difference come from ? Thanks in advance
  17. G

    B Could Copper's 29th Ionization Energy Be Used to Create Uranium-235?

    So I was playing with periodic table and discovered Cu's 29th ionization energy(cu with no electron) is 1116105 KJ/mole . Then i searched on google to convert to MeV which is 6.9661798e+21 , then I thought that one uranium 235 produce 200mev so to make that you would need around 3.5e+19...
  18. T

    Standard electrode potential vs ionization energy

    Here is the Wikipedia page on electrode potentials. Here's how I'm reading it, which makes no sense: If a singly ionized atom of strontium donates an electron to the hydrogen in the standard hydrogen electrode, this will emit 4.101 eV of heat (395.68 kJ/mol). If cesium is used, there will be...
  19. Turbotanten

    Find the ionization energy of a simple model atom

    1. Homework Statement A simple model atom is composed of a point-like nucleus with charge ##+Q## and an electron charge distribution $$ \rho(\vec{r})=-\dfrac{\left|Q\right|}{\pi a^2 r}exp(-2r/a) $$ where ##a## is a constant. Show that the ionization energy (the energy to remove the electron to...
  20. T

    Deriving the ionization energy of a hydrogen atom

    Hi, I've just gotten started with basic quantum physics in physics class and we've just talked about ionization energy. It is stated that the energy of a hydrogen atom is -13.60eV (or -2.179aJ). I assume this is the potential energy (and that this is the reason the atom has a lower mass than the...
  21. B

    Ionization energy of an electric field

    Hi, If I had a charged parallel plate capacitor which was not connected to a circuit (so the charges stay on the plates) creating an electric field strong enough to cause ionization, and I then fired a neutral atom between the charged plates (the charge starts outside of the electric field)...
  22. Magnetic Boy

    Ionization Energy: Homework Problem Solving

    Homework Statement .[/B] Suppose the energy difference between the states n=2 and n=3 is E(eV), in an hydrogen atom. then the ionization potential in volts is: A) 13.2E B) 7.2E C) 3.2 E D) 0.56E Homework Equations En = -13.7 × Z^2÷n^2 The Attempt at a Solution I just know the ionization energy...
  23. P

    Ionization Energy of Helium Atom | 24.6 eV

    Homework Statement The energy required to ionize a helium atom is 24.6 eV. The energy required to remove both the electrons from He atom would be?The Attempt at a Solution My textbook says- IP1= 24.6 eV IP 2= IP1*Z2 How can they relate the first ionization energy to the second one? The Bohr's...
  24. H

    Atomic radius and Ionization Energy Trends?

    My teacher was not too clear about this and from what I've gathered is if you're given two elements this is how you would figure out which one has a larger atomic radius or ionization energy, but I'm not sure if it's accurate Radius: Whichever one is in a lower period (more energy levels) has a...
  25. C

    Electric Potential and Ionization Energy of Bohr Hydrogen

    I was studying for (first year) physics class and was playing around with the Bohr Model of Hydrogen. I tried calculating the electric potential at the Bohr radius r =5.29e-11 m, where V = \frac{e}{4 \pi \epsilon_0 r} (from the point-charge formula for electric potential) and I got 27.19 J/C...
  26. S

    Understanding First Ionization Energy for Diatomic Gases

    When looking at ionization energy charts; specifically for diatomic gasses, are we looking at the energy to take 1 electron from atomic or diatomic gasses?
  27. V

    Ionization Energy: Who Has the Highest?

    Homework Statement Which of the following atoms has the largest first ionization energy? Potassium, Zinc, Gallium, or Krypton? Homework Equations No equation The Attempt at a Solution Krypton has the largest first ionization energy, but I was wondering how this question would be...
  28. gracy

    Ionization ENERGY -Why removal of electron from gaseous atom

    Why ionization energy is defined as the energy required to remove the outermost, or highest energy, electron from a neutral atom in the gas phase. Why can't we remove electrons from a solid,can we? If not ,what's the reason?I think we can not remove electrons from a solid because in gas phase...
  29. H

    First Ionization energy exceptions

    I'm having a hard time understanding the first ionization energy exception between the s and p block. My book tries to explain it but I feel like it is a poor explanation. It states that the ionization energy for Boron is actually lower than Beryllium because of the fact that the p block is...
  30. F

    Ionization energy calculations

    Why isn't the ionization energy of an electron equal to it's energy level such that: E(electron)= -13.6(Z^2/n^2) = IP for that electron But instead it is equal to the energy difference in energy between the atom and its ionized cation: IP = E(A)-E(A+)
  31. N

    How ionization energy can be lower than band gap?

    I am reading about the ionization energy in semiconductors and came across this thing that for Silicon, the ionization energy is lower than its band gap energy. I don't understand how can this be?
  32. N

    How Do You Calculate Ionization Energies for Different Shells in X-ray Spectra?

    Homework Statement The K series of the discrete x-ray spectrum of tungsten contains wavelengths of 0.018 5 nm, 0.020 9 nm, and 0.021 5 nm. The K-shell ionization energy is 69.5 keV. (a) Determine the ionization energies of the L, M, and N shells. Homework Equations E=\frac{hc}{\lambda}...
  33. O

    Ionization Energy QNS - Get Help Now!

    Hi, I am slightly confused with the term, ionization energy (IE). I am stuck between two definitions, one is the minimum energy to remove an outermost electron from an atom while the other is the energy to completely remove an electron from ground state. If its the former, wouldn't it have a...
  34. G

    Energies higher than ionization energy

    Homework Statement During a discussion, we tried to figure out, according to the Bohr model of the atom, what happens when radiation with a higher energy level than that which can ionize hydrogen. Homework Equations Absorption spectrum of hydrogen. Ionization energy of hydrogen - 13.6...
  35. P

    Calculate the Second Ionization Energy of Lithium

    Homework Statement Given -Total Energy for Li \rightarrow Li ^{3+} = 1.960 * 10^{4} kJ/mol -First Ionization Energy of Li = 5.20 * 10^{2} kJ/mol Homework Equations Other than the equation in the image, I used the equation: Etotal = E1 + E2 + E3 The Attempt at a Solution Since Etotal and...
  36. V

    Ionization Energy (Quantum Mechanics)

    Homework Statement When ultraviolet radiation of wavelength 58.4 nm from a helium lamp is directed on to a sample of krypton, electrons are ejected with a speed of 1.59 Mm/s. Calculate the ionization energy of Krypton.Homework Equations E=hv, \frac{1}{λ}=R(1- \frac{1}{n2} ) <- Lyman series...
  37. W

    Ionization Energy of Lithium problem

    The energy needed to strip all three electrons from a Li(g) atom was found to be 1.96*10^4 kJ/mol. The first ionization energy of Li is 520 kJ/mol. Calculate the second ionization energy of Lithium atoms (the energy required for the process) Li+(g) ---> Li+2 + e- Equation: frequency =...
  38. B

    Calculating second ionization energy of He

    Homework Statement The equation En=-Z2RH/n2 gives the energy (according to the Bohr model) of the energy levels available to an electron in any hydrogen-like atom. Calculate the second ionization energy of He(in J). The second ionization energy of He is the ionization energy of He+. Homework...
  39. C

    Ionization energy - compare 2 unknown elements and decide their group

    Hello. I have a question about ionization energy: Two hypothetical elements in the 2nd or 3rd period have the following ionization energies: Element X First: 800 kJ/mol Second: 2500 kJ/mol Third: 3900 kJ/mol Fourth: 23000 kJ/mol Element Y First: 700 kJ/mol Second: 2200 kJ/mol...
  40. fluidistic

    Ionization energy of the dihydrogen

    Homework Statement Calculate the energy of ionization of the dihydrogen H_2, knowing that the binding energy of H_2 and H_2^+ are worth -4.48 eV and -2.65 eV respectively and that the ionization energy of the hydrogen atom is 13.6 eV.2. Relevant thoughts Energy of ionization of H_2 is the...
  41. C

    Calculating volume of plasma per watt, based on ionization energy

    This is not homework, but I'm developing a new machine and doing my own research as a mechatronical engineer. I'm trying to calculate the maximum volume of Helium gas that can be ionized into plasma if I apply a power of 1 watt, where the voltage is 1000 volt and the current is 0,1mA. DATA...
  42. C

    Plasma volume & Ionization Energy relationship

    I'm trying to calculate the maximum volume of Helium gas that can be ionized into plasma if I apply a power of 1 watt, where the voltage is 1000 volt and the current is 0,1mA. The ionization energy for Helium is 2372,3KJ/mol (1/2372,3*10^3)mole * 2372,3*10^3 J/mole = 1 Joule 1 Watt = 1...
  43. K

    Calculating Ionization Energy of Elements Beyond H

    Can anyone tell me which formula is used to calculate the ionization energy of elements different then H. E= Z^2 13,6eV/ n^2 where n- number of the shell, and Z- number of protons only gives the ionization energy in case of one electron around the nucleus. Thank you in advance.
  44. T

    Electronic Band Structure, Ionization Energy

    Hi, thanks for reading my questions. I've been reading and reading and reading and reading and I'm trying to understand the difference between conductors, semiconductors, and insulators at an atomic level. When reading about electricity I often find that metals have a "sea" of "free"...
  45. H

    What is the Ionization Energy of Lithium?

    Homework Statement Estimate the ionization energy of Lithium. Neglect the repulsion between the electrons. Homework Equations what is the equation that can be used here? There are thousands of tables in the web having tabulated the values of various ionaziation energies. But one can hardly...
  46. fluidistic

    How to Estimate Z Effective for Alkali Atoms Using Ionization Energy?

    Homework Statement Consider an alkali atom in its fundamental state and assume that its valence electron experiment a constant shielding with Z_{eff}>1. Use the tabulated values of the ionization energy to estimate Z_{eff} for the Li, Na and K atoms. Homework Equations I do not know...
  47. fluidistic

    Difference between ionization energy and work function

    I'm looking at the ionization energy of some elements and their work function. To my astonishment these energies are quite different (factor close to 2). How is that possible that if say a piece of copper has almost all its atoms in the fundamental state (room temperature ensures this I...
  48. G

    Why Should n Be 1 When Calculating I3 for Lithium Using the Rydberg Formula?

    Hello all- I am working to calculate the value of I3 for Li. I am working through the formula: Z2hR/n2 Can anyone tell me what n is equal to? I had originally set n=3 since I am looking for I3, but it was marked incorrect as n should have been set at 1. I'm not sure why in this case...
  49. M

    Ionization Energy in Electron Volts

    Homework Statement (10.) It requires roughly 10 eV to ionize one hydrogen atom. How much energy (in joules) are needed to ionize all the hydrogen atoms in one mole of molecular hydrogen (H2)? [Recall: 1 eV = 1.6 × 10−19 J and Avogadro’s constant is about 6 × 1023.] Homework Equations...
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