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This page explains what the first ionization energy is and then looks at how it varies across the periodic table - across different periods and subgroups. It assumes you know simple atomic orbitals and can write electronic structures for simple atoms.
Definition: First ionization energy
The first ionization energy is the energy needed to remove the most loosely bound electron from the moleneutralgaseous atoms to produce1 molgaseous ions, each of which has a charge1+.
This is easiest to see in terms of symbols.
\[ X(g) \right arrow X^+(g) + e^-\]
This is the energy needed to cause this change per mole \(X\). State symbols - (g) - are required. When you talk about ionization energies, everything must exist in a gaseous state. Ionization energies are measured in kJ mol-1(kilojoules per mole). Their sizes range from 381 (which you consider too low) to 2370 (which is too high).
All elements have a first ionization energy - even atoms that do not form positive ions in test tubes. The reason why helium (1 I.E. = 2370 kJ mol-1) does not normally form a positive ion due to the enormous amount of energy that would be required to remove one of its electrons.
First trends of ionization energy
The first ionization energy shows periodicity.This means that it changes in a repetitive way as you move around the periodic table. For example, look at the pattern from Li to Ne, then compare it to the same pattern from Na to Ar. All these changes in the first ionization energy can be explained in terms of the structures of the atoms involved.
Factors affecting the amount of ionization energy
Ionization energy is a measure of the energy required to pull a particular electron away from the attraction of the nucleus. A high value of ionization energy indicates a strong attraction between the electron and the nucleus. The size of this attraction will be determined by:
- Core charge:The more protons there are in the nucleus, the more positively charged the nucleus is and the stronger the electrons are attracted to it.
- The distance of the electron from the nucleus:Traction decreases very quickly with distance. An electron closer to the nucleus will be attracted much more strongly than an electron farther away.
- The number of electrons between the outer electrons and the nucleus:Consider a sodium atom with an electronic structure of 2,8,1. (There's no reason why you can't use this note if it's useful!)
If the outer electron is pointed towards the nucleus, it cannot see the nucleus sharply. Between it and the nucleus are two layers of electrons in the first and second levels. The 11 protons in the sodium nucleus are bounded by 10 inner electrons. Therefore, the outer electron only feels a net attraction of about 1+ from the center. This reduction in the attraction of the nucleus to the inner electrons is known as shielding or shielding.
- Whether an electron is alone in an orbital or paired with another electron:Two electrons in the same orbital experience some repulsion from each other. This compensates for the attraction of the nucleus, so that the paired electrons are removed much more easily than one might expect.
Example 1: Sun vs. Lit
Hydrogen has a 1s electronic structure1. It is a very small atom and a single electron is close to the nucleus and therefore strongly attracted. There are no electrons to separate it from the nucleus, so the ionization energy is high (1310 kJ mol-1).
- Helium has a structure of 1s2. The electron is removed from the same orbital as in the case of hydrogen. It is close to the core and is not controlled. The value of the ionization energy (2370 kJ mol-1) is much higher than hydrogen because the nucleus now has 2 electron-attracting protons instead of 1.
- Lit to 1s22s1. Its outer electron is in the second energy level, much further from the nucleus. One could argue that this would be offset by the extra proton in the nucleus, but the electron doesn't feel the full pull of the nucleus - it's controlled for 1s2electrons.
You can think of the electron as a net 1+ attraction from the center (3 protons are displaced by two 1's).2electrons). If you compare lithium with hydrogen (instead of helium), the hydrogen electron also feels a 1+ pull from the nucleus, but the distance is much greater with lithium. The first ionization energy of lithium drops to 519 kJ mol-1while hydrogen has 1310 kJ mol-1.
Patterns in periods 2 and 3
Discussing the next 17 people individually would take years. We can do this much more thoroughly by explaining the major trends during these periods and then considering the exceptions to those trends. The first thing to realize is that the patterns in both periods are identical - the difference is that the ionization energies in period 3 are lower than in period 2.
Explanation of the general trend in periods 2 and 3
The general trend is that ionization energies increase over a period of time. Throughout the period, the 2 outer electrons are in 2-level orbitals - 2s or 2p. They are all the same distances from the core and controlled by the same ones2electrons.
The main difference is the increasing number of protons in the core as you go from lithium to neo. This causes more attraction between the nucleus and the electrons and thus increases the ionization energy. In fact, the increasing nuclear charge also attracts the outer electrons closer to the nucleus. This increases the ionization energy even more during your period.
In period 3, the trend is exactly the same. This time all removed electrons are in the third level and are controlled by 122s22 str6electrons. They all have the same type of environment, but the nuclear charge increases.
Why the decrease between groups 2 and 3 (Be-B and Mg-Al)?
The explanation lies in the boron and aluminum structures. The outer electron is removed from these atoms more easily than the general trend in their period would suggest.
| Is |  | 1s22s2 | | 1. I.E. = 900 kJ mol-1 |
| and |  | 1s22s22 strX1 | | 1. I.E. = 799 kJ mol-1 |
The value of boron can be expected to be higher than that of beryllium due to the extra proton. This is compensated by the fact that boron's outer electron is in a 2p orbital rather than a 2s. The 2p orbitals have slightly higher energy than the 2s orbitals, and the electron is on average farther from the nucleus. This has two implications.
- Increased distance results in reduced attraction and therefore reduced ionization energy.
- The 2p orbital is not only controlled by 1s2electrons, but to some extent in 2s2electrons too. This also reduces the attraction from the nucleus and thus lowers the ionization energy.
The explanation for the drop between magnesium and aluminum is the same, except that everything happens in plane 3, not plane 2.
| Mg | | 1s22s22 str63s2 | | 1. I.E. = 736 kJ mol-1 |
| Lap |  | 1s22s22 str63s23pX1 | | 1. I.E. = 577 kJ mol-1 |
The 3p electron in aluminum is slightly further from the nucleus than the 3s electron and is partly controlled by the 3s2electrons and internal electrons. Both of these factors offset the effect of the extra proton.
Why the decrease between groups 5 and 6 (N-O and P-S)?
Again, one would expect the ionization energy of a group 6 element to be higher than a group 5 element due to the extra proton. What makes up for it this time?
| N | | 1s22s22 strX12 stry12 strz1 | | 1. I.E. = 1400 kJ mol-1 |
| TO | | 1s22s22 strX22 stry12 strz1 | | 1. I.E. = 1310 kJ mol-1 |
The projection is identical (from 12and to some extent from 2s2electrons), and an electron is removed from an identical orbital. The difference is that in the case of oxygen, the electron being removed is one of the 2p electronsX2couple. The repulsion between two electrons in the same orbital means that the electron is removed more easily than otherwise. The decrease in the ionization energy of sulfur is calculated in the same way.
Ionization energy trends down the group
As you move down a group in the periodic table, the ionization energies generally decrease. You have already seen evidence of this in the fact that the ionization energies in period 3 are less than in period 2. Taking group 1 as a typical example:
Why is the price of sodium lower than lithium? There are 11 protons in a sodium atom, but only 3 in a lithium atom, so the nuclear charge is much greater. One would expect a much higher ionization energy for sodium, but the trade-off for nuclear charge is greater distance from the nucleus and greater control.
| Li | | 1s22s1 | | 1. I.E. = 519 kJ mol-1 |
| Already | | 1s22s22 str63s1 | | 1. I.E. = 494 kJ mol-1 |
Lithium's outermost electron is on the second level and is only 1s2electrons to test it. 2 sec1The electron feels the attraction of 3 protons controlled by 2 electrons - net attraction from the 1+ center. Sodium's outer electron is in the third level and is controlled by 11 protons in the nucleus out of a total of 10 inner electrons. 3 sec1The electron also experiences a net 1+ attraction from the center of the atom. In other words, the effect of the extra protons is offset by the effect of the extra shielding electrons. The only remaining factor is the extra distance between the outer electron and the nucleus in the case of sodium. This reduces the ionization energy.
Similar explanations apply when you go below the rest of the team - or indeed any other team.
Ionization energy trends in the transition series
With the exception of zinc at the end, the other ionization energies are about the same. All of these elements have the electronic structure [Ar]3dN4s2(or 4 sec1for chromium and copper). The lost electron always comes from the 4s orbital.
As you go from one atom to another in a series, the number of protons in the nucleus increases, but the number of 3d electrons also increases. The 3d electrons have some shielding effect, and the extra proton and the extra 3d electron almost cancel each other out in terms of attraction from the center of the atom.
The increase in zinc is easy to explain.
| Cu | | [Ar]3d104s1 | | 1. I.E. = 745 kJ mol-1 |
| zn | | [Ar]3d104s2 | | 1. I.E. = 908 kJ mol-1 |
In each case, the electron comes from the same orbital, with identical control, but the zinc has an extra proton in the nucleus, so the attraction is greater. There will be some degree of repulsion between the paired electrons in the 4s orbital, but in this case obviously not enough to offset the effect of the extra proton.
Ionization energies and chemical reactivity
The lower the ionization energy, the easier this change occurs:
\[ X(g) \right arrow X^+(g) + e^-\]
You can explain the increase in reactivity of the group 1 metals (Li, Na, K, Rb, Cs) as you move down the group in terms of a decrease in ionization energy. Whatever these metals react with, they must form positive ions in the process, so the lower the ionization energy, the easier these ions will form. The danger with this approach is that creating a positive ion is just one step in a multi-step process.
For example, you wouldn't start with gas atoms. you won't end up with gaseous positive ions either - you'll end up with ions in a solid or solution. The energy changes in these processes also vary from element to element. Ideally, you should consider the entire image, not just a small part of it.
However, the ionization energies of the elements will be the major contributors to the activation energies of the reaction. Remember that activation energy is the minimum energy needed for a reaction to occur. The lower the activation energy, the faster the reaction will be - regardless of what the total energy changes in the reaction are.
The decrease in ionization energy as you move down the group will lead to lower activation energies and thus faster reactions.
Contributions and references
Jim Clark (Chemguide.co.uk)
FAQs
What are real life examples of ionization? ›
A familiar example of ionizing radiation is that of x-rays, which can penetrate our body and reveal pictures of our bones. We say that x-rays are “ionizing,” meaning that they have the unique capability to remove electrons from atoms and molecules in the matter through which they pass.
What is ionization in physical science? ›Ionization is the process by which ions are formed by gain or loss of an electron from an atom or molecule. If an atom or molecule gains an electron, it becomes negatively charged (an anion), and if it loses an electron, it becomes positively charged (a cation).
What is teaching about ionization energy? ›Lesson Summary. Overall, ionization energy is the minimum amount of energy required to remove an atom's outermost electron(s). The periodic table of elements is organized so that a trend in ionization energy can be seen across and throughout periods and groups.
What are the 2 types of ionization energy? ›Ionization of molecules often leads to changes in molecular geometry, and two types of (first) ionization energy are defined – adiabatic and vertical.
What are 3 examples of ionization? ›Examples of these processes include the reaction of a sodium atom with a chlorine atom to form a sodium cation and a chloride anion; the addition of a hydrogen cation to an ammonia molecule to form an ammonium cation; and the dissociation of a water molecule to form a hydrogen cation and a hydroxide anion.
What are examples of ionization in water? ›Water becomes ionized when you dissolve something in it. For example, if you dissolve salt into water, the sodium atoms in the salt molecules separate slightly from the chloride atoms.
Does salt ionize in water? ›Water molecules pull the sodium and chloride ions apart, breaking the ionic bond that held them together.
How can a gas be ionized? ›A plasma is an ionized gas that results when a basic gas, such as nitrogen or air is passed through an electrical arc struck between two electrodes.
What is ionization of water in biology? ›Self Ionization of Water
Water will self-ionize to a very small extent under normal conditions. The reaction in which a water molecule donates one of its protons to a neighbouring water molecule, either in pure water or in an aqueous solution, is called the self-ionization of water.
Kids Encyclopedia Facts. Ionization is the physical process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or other ions. This process works slightly differently depending on whether an ion with a positive or a negative electric charge is being produced.
What is first ionization energy for dummies? ›
The first ionization energy is the energy required to remove the most loosely held electron from one mole of neutral gaseous atoms to produce 1 mole of gaseous ions each with a charge of 1+. This is more easily seen in symbol terms. It is the energy needed to carry out this change per mole of X.
What is ionization energy for kids? ›Ionization energy is the energy needed to take an electron from an atom. The atom is not connected to any other atoms. The chemical elements to the left of the periodic table have a much lower ionization energy.
What are the types of ionization techniques? ›- Electron Impact (EI) ...
- Chemical Ionization (CI) ...
- Field Ionization/Desorption. ...
- Electrospray Ionization (ESI) ...
- Matrix Assisted Laser Desorption Ionization (MALDI) ...
- Inductively Coupled Plasma Mass Spectrometry (ICP-MS)
Ionization energy tells us how likely an atom is to form a cation, and if so, what charge. In general, it tells us how tightly the electron is bound, how stable it is. It can tell us the energies of real orbitals, the effects electrons have on each other, and help us predict reactivity and properties of molecules.
What are the four factors affecting ionization energy? ›- the size of the atom.
- the charge on the nucleus.
- how effectively the inner electron shell screen the nuclear charge.
Ionization Methods With Selected Ion Monitoring
Electron ionization (EI) is the most commonly used ionization technique and it employs energetic electrons that generally induce a high degree of fragmentation of the analyte. EI fragmentation typically generates a range of ions that may be monitored in SIM.
The ionization energy decreases from top to bottom in groups, and increases from left to right across a period. Thus, helium has the largest first ionization energy, while francium has one of the lowest.
What kind of energy is ionization? ›The ionization energy is the quantity of energy that an isolated, gaseous atom in the ground electronic state must absorb to discharge an electron, resulting in a cation. This energy is usually expressed in kJ/mol, or the amount of energy it takes for all the atoms in a mole to lose one electron each.
What are 3 substances that ionize in water? ›Arrhenius acids include compounds such as HCl, HCN, and H2SO4 that ionize in water to give the H+ ion. Arrhenius bases include ionic compounds that contain the OH- ion, such as NaOH, KOH, and Ca(OH)2.
Does sugar ionize in water? ›Even after dissolving in water, sugar molecules retain their form and do not turn into ions.
Does sugar break into ions? ›
Answer and Explanation: The sugar molecule is considered a nonelectrolyte and it does not dissociate into ions when dissolved in water.
Is tap water ionic? ›Tap water contains ions and salts while distilled water is a pure form of water used in chemical reactions.
Can electricity be ionized? ›Ionization by Electric Fields
If there is a sufficient path length, the electrons may gain enough kinetic energy to produce secondary electrons by impact ionization, leading to an avalanche type breakdown. A very similar process may occur in solids, particularly semiconductor devices.
Air is a mixture of gases including nitrogen, oxygen, carbon dioxide, water vapor, and other trace gases, any one or more of which can be ionized. When any one or more of these gas molecules gains or loses an electron, it becomes charged and thus called air ions.
Is fire ionized gas? ›Those atoms, which are left with an excess positive charge, are called "ions," and those particles as well as the gas are said to be "ionized." All regions of a flame will contain at least some charged particles and, therefore, will be ionized.
How does water self ionize? ›The self-ionization of water (also autoionization of water, and autodissociation of water) is an ionization reaction in pure water or in an aqueous solution, in which a water molecule, H2O, deprotonates (loses the nucleus of one of its hydrogen atoms) to become a hydroxide ion, OH−.
What increases ionization of water? ›The value increases as the temperature rises, indicating that the concentration of H+ and OH- ions increases as the temperature rises.
What happens if water is ionized? ›When water in a water ionizer is ionized, it is split into two separate streams of water. One of those streams is alkaline, the other one is acidic.
What is the difference between ionized and ionization? ›Ionization and ionisation are both English terms. Ionization is predominantly used in 🇺🇸 American (US) English ( en-US ) while ionisation is predominantly used in 🇬🇧 British English (used in UK/AU/NZ) ( en-GB ). In the United States, there is a preference for "ionization" over "ionisation" (99 to 1).
Is ionization good or bad? ›Ionizers are highly effective at removing particulate matter (PM) from the air and some surface particulates. On their own, ionizers produce too much ozone and can be harmful to people's health.
What are the first five ionization energies? ›
The first five ionization energies of an element are 9.1, 16.2, 24.5, 35 and 205.7 eV respectively. The number of valence electrons in the atom is. No worries! We've got your back.
What is ions in simple words? ›ion, any atom or group of atoms that bears one or more positive or negative electrical charges. Positively charged ions are called cations; negatively charged ions, anions.
What is ionization energy in easy words? ›The ionization energy is a measure of the capability of an element to enter into chemical reactions requiring ion formation or donation of electrons. It is also generally related to the nature of the chemical bonding in the compounds formed by the elements.
What are three ionization energy? ›The third ionization energy is the energy it takes to remove an electron from a 2+ ion. (That means that the atom has already lost two electrons, you are now removing the third.) And 2nd ionization energy is higher than 1st ionization energy, 3rd is higher than 2nd, and so forth.
Which is the softest ionization technique? ›We found that Cold PI is as soft as and possibly softer than field ionization; thus, it could be the softest known ionization method.
How do you choose ionization techniques? ›The most important considerations for selecting an ionization technique are the physical state of the analyte and the ionization energy needed. Electron ionization and chemical ionization are only suitable for gas phase ionization.
What triggers ionization? ›Ionization can result from the loss of an electron after collisions with subatomic particles, collisions with other atoms, molecules and ions, or through the interaction with electromagnetic radiation. Heterolytic bond cleavage and heterolytic substitution reactions can result in the formation of ion pairs.
What determines high ionization energy? ›If you must determine which element from a list has the highest ionization energy, find the elements' placements on the periodic table. Remember that elements near the top of the periodic table and further to the right of the periodic table have higher ionization energies.
What tends to have high ionization energy? ›Therefore, noble gases will have the highest ionisation energy.
What is a real life example of common ion effect? ›An example of the common ion effect can be observed when gaseous hydrogen chloride is passed through a sodium chloride solution, leading to the precipitation of the NaCl due to the excess of chloride ions in the solution (brought on by the dissociation of HCl).
What is an example of an atom that ionizes? ›
Chlorine atoms often become ionized by gaining an electron in order to stabilize their outer orbital configuration. The addition of an electron means that chlorine becomes ionized with a negative charge. The symbol for ionized chlorine is Cl-.
What is a simple example for ionization isomerism? ›In ionization isomerism compounds give different ions in solution to the exchange of ions in the coordination sphere and the counter ion present in the complex. Hydration or Solvate Isomerism is a special type of ionization isomerism. The best example of this occurs for chromium chloride “CrCl3.
What is a real life example of a pure element? ›Examples of Pure Substances
All elements are mostly pure substances. A few of them include gold, copper, oxygen, chlorine, diamond, etc. Compounds such as water, salt or crystals, baking soda amongst others are also grouped as pure substances.
The principle of common-ion effect applies in many chemical processes including those involved in buffering solutions, purification of salts, salting out of soap, precipitation of salts, manufacture of baking soda and water treatment (This study).
How are ions important in everyday life? ›Transmit nerve signals, and contract muscles including the heart, etc. Contract muscles, form bones and teeth, activate enzymes, etc. Regulate osmotic pressure and the body's water content, enable the secretion of stomach acid, etc.
What is common ion effect activity? ›The common ion effect describes the effect on equilibrium that occurs when a common ion (an ion that is already contained in the solution) is added to a solution. The common ion effect generally decreases solubility of a solute.
What element has ionization? ›| Ionization Energy | Name chemical element | Symbol |
|---|---|---|
| 3,8939 | Cesium | Cs |
| 4,0727 | Francium | Fr |
| 4,1771 | Rubidium | Rb |
| 4,3407 | Potassium | K |
Electrolytes are substances which, when dissolved in water, break up into cations (plus-charged ions) and anions (minus-charged ions). We say they ionize. Strong electrolytes ionize completely (100%), while weak electrolytes ionize only partially (usually on the order of 1–10%).
What is an example of ionization of gas? ›Everyday examples of gas ionization are such as within a fluorescent lamp or other electrical discharge lamps. It is also used in radiation detectors such as the Geiger-Müller counter or the ionization chamber.
What is ionization energy formula with examples? ›Ionization Energy Example
The ionization energy = + 2.18 × 10–18 J/atom (or + 1312.3 KJ/mole). So the amount of optimum energy required for the elimination of the second electron away from the unipositive ion is termed as the second ionization energy. The procedure is the same for more outputs.
What are some daily life examples of isomerism? ›
The substituted xanthines are a good example of an isomer found in food and drugs. Theobromine, caffeine, and theophylline are isomers, differing in the placement of methyl groups. Another example of isomerism occurs in phenethylamine drugs.
What is the most commonly used ionic substance in home? ›Table Salt. Perhaps the most common ionic compound people come across every day is table salt. The chemical name of table salt is sodium chloride, NaCl. It has a cubic unit cell.
What are 5 common household items that are pure substances? ›Examples of pure substances include tin, sulfur, diamond, water, pure sugar (sucrose), table salt (sodium chloride) and baking soda (sodium bicarbonate).
What are 3 real world examples of elements? ›- Carbon- Our body is made up of 18% Carbon. ...
- Hydrogen- It is used in the synthesis of water which is essential for life. ...
- Oxygen- It is essential for respiration, circulation, and many more physiological processes. ...
- Chlorine- It is used as a disinfectant for water. ...
- Sulphur-It is used in the synthesis of Sulfuric acid.