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# First and second ionization energy

An element's second ionization energy is the energy required to remove the outermost, or least bound, electron from a 1+ ion of the element. Because positive charge binds electrons more strongly, the second ionization energy of an element is always higher than the first. Created by Jay.

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• Would there be such a thing as third ionization energy? Also, if the third electron from Lithium would be pulled away would take the same amount of force as the second or would this in turn be even harder to pull away?
• There is most certainly a third ionization energy, and fourth, and fifth....! The 3rd IE corresponds to the energy required to remove an electron from the gaseous M2+ species of any element, i.e. Na2+, Ca2+, or S2+. As you remove more and more electrons, the atom becomes progressively more positively charged, Hence, it becomes harder and harder to remove an electron, which is negatively charged.

Each successive ionization energy would be larger in magnitude than the previous one. The ionization energy that corresponds to removing an electron from the noble gas configuration would be substantially higher than those before. For example, for P, the 5th IE is 6,270, while the 6th IE is 21,200. For Al, the 3rd IE is 2,881, while the 4th IE is 11,600.
• you stated that the first ionization energy for Li is 520 kj/mol and the second ionization energy is 7298kj/mol. how would you calculate those ionization energy values for Li and also take the value of the shielding constant into consideration. thank you.
• What is z in the equation (meaning)
• Does size of the atom have a relation between nuclear charge and ionization energy? Would it correct to conclude that larger the atom, lower the ionization energy (since distance from the nucleus is higher)?
• Great question! The size of an atom does affect both the nuclear charge and the ionization energy. First of all, If an atom has more protons in its nucleus, then the nuclear charge will obviously be greater, so the ionization energy will be higher. But just as Jay said, you also have to take into account the distance between the electrons and the nucleus, as well as electron shielding/screening. A larger atom will have more distance between the nucleus and the farthest electrons, so it will be easier for that atom to lose an electron. Also, a larger atom will have more electrons, which will all repel each other and push the outer electrons away from the nucleus (at least, that's what I would think). Both of these factors will lower the ionization energy. So I believe you are correct in that the larger the atom, the lower the ionization energy will be. (Sorry, I know this answer is late in coming.)
• I'm trying to understand the concept of joules in relation to pulling an electron away. I am used to using watts (and amps and volts) as measurement for energy and watts can be experienced through things like electroshock therapy, but something like 7 joules sounds like lightbulb that would be too bright to make a meaningful difference other than as a heat lamp.
So, can this instead be conceptualized as how many pounds a would be needed to pull an election away if you could clamp an atom down and tie a string to one election? or even better in terms of pulling one magnet from a 1 pound piece of mild steel? I'm a bit of a meathead coming from a blacksmithing background so please bear with me.
(1 vote)
• I think it would be helpful here to go over the fundamental definitions of energy and all the units you’ve listed here to better understand ionization energy.

Energy itself, viewed from a physics perspective, is defined as the capacity to do work. Work, in the physics sense, is the result of a force acting over a distance. And a force is a pushing or pulling motion which causes an object to accelerate.

So if we imagine pushing (applying a force) an object, any object, a certain distance over say a table’s surface, then we would say we have performed work on that object. In essence what we did was transfer some of our own energy into the object to facilitate the object’s motion. So something is said to possess energy if it can do work. There are many different types of energies; electrical, mechanical, thermal, gravitational, chemical, etc., but we can generalize and categorize energies as either potential or kinetic energy. Potential energy is related to an object's position (where it is); or in other words it has the potential to do work but it’s currently not doing so. Kinetic energy is energy related to an object’s motion; if an object is moving in some manner then it has kinetic energy. Most objects do not have either entirely potential or kinetic energy, and instead possess a combination of the two (which combined are that object’s total energy).

Now looking at the units of force, work, and energy. In SI units, the unit of force is the newton (N), and the American customary unit is the pound-force (not to be confused with the pound-mass). Mathematically work is defined as the product of force and distance, F x d = w, where the SI unit of distance is the meter (m) and newton for force (and ‘w’ is the usual variable for work). So the SI unit for energy is the newton-meter (Nm), more commonly referred to as the joule (J). Since energy is related to work, energy’s unit is also the joule. In America the units of energy are foot-pounds or British thermal units (BTU). So this means 1 joule of energy is the amount of energy required to apply a 1 newton force on an object for a distance of 1 meter.

Watts (W) aren’t actually a unit of energy, rather a unit of power. Power is the amount of energy expended per unit of time, Power = energy/time. So 1 watt would be if we applied 1 joule of energy per 1 second to something. Using that power equation, we can get another commonly used energy unit called the kilowatt-hour (kWh), which is defined as the amount of energy needed to provided 1000 watts of power for 1 hour.

Amperes (A), or amps for short, aren’t a unit of energy either, rather a unit of electric current. If we imagine electrons moving in a wire (essentially what electricity is) like water in a stream, then we have a current in that wire. Current is defined as the amount of electrical charge (usually electrons) flowing per unit of time, current = charge/time. So 1 amp of current is defined as the flow of 1 coulomb (the unit for electrical charge) of charge per 1 second.

Volts (V) too aren’t a unit of energy, but they are closely related. Voltage can be thought of as the driving force which propels electrons and creates a current in a wire. Since electrons are negatively charged they are naturally attracted to positively charged objects (and repelled from negatively charged objects). So any kind of electrical device has a positively charged component which electrons travel towards, and a negatively charged component which they travel away from (collectively called electrodes). Electrical current is driven by a difference in potential energy caused by an electric field resulting from the charge difference on the two electrodes. This is why voltage is also referred to as potential difference or electrical potential. As an equation we can think of voltage as the amount of energy possessed by charge carriers (again almost always being electrons), Voltage = energy/charge. So using SI units, 1 volt is a difference of 1 joule of potential energy (J) per 1 unit of charge (C). So while voltage isn’t energy, it is closely related to energy and like watts we can create yet another common unit of energy called the electron-volt (eV). 1 electron-volt is the amount of kinetic energy gained by an electron as it passes through a voltage of 1 volt.

Now looking at ionization energy. Ionization energy is the amount of energy we need to input into an atom to remove an electron from that atom. If we think of it as work, it’s the amount of force we need to apply to the electron to move it a certain distance from the nucleus of the atom so that they no longer feel a force of attraction (because they have opposite charges). This means we could think of it as us pulling on the electron with a certain amount of pounds (force-pounds) so that it is sufficiently far from the nucleus the overcome the electrical attraction the two feel. The magnet analogy would also work (Ha) because we would be exerting a force on the steel in order to move it a certain distance so that it no longer felt a force of attraction. The work being done is attempting to overcome the magnetic force in the same way that ionization energy is work done to overcome the electric force.

When ionization energies are calculated experimentally we usually expose them to light of sufficient energy. The light transfers energy to the electron and grants it enough kinetic energy to escape from the pull of the protons on the nucleus. We measure the ionization energy based on the energy of the light required to ionize the atom.

Hope that helps.
• So can we also remove the last electron of Lithium ?
• To remove the last electron, people say it would take a lot to do it, but more specifically it takes 11,815 KJ/mol.
• is it possible that lithium can lose its 1s1 electron as well and turn into Li3+?
• It is possible but that would require a really high amount of energy to be supplied to the Li2+ ion.
• Why is the first ionisation energy of Helium is more than that of Hydrogen ?
Thank you.
• First I.E of He is more than that of H because He has two valence electrons and its charge is also greater than that of H . Also it is a noble gas and very stable , so we have to provide larger energy to remove an electron from its outer most shell.
• How to calculate Ionization energy using Slater's Rules?
• So slater's rules help calculate the effective nuclear charge which quantifies the attraction an electron feels for an atom's nucleus. Ionization energy is the amount of energy needed to remove an electron from a neutral gaseous atom and form an ion. The stronger an electron is bound to an atom the more ionization energy it requires, therefore these two are directly proportional.

As for calculating the actual values we can use a modified form of the Rydberg formula to do so: E = RH (Zeff^(2)/n^(2)), where E is the ionization energy, Zeff is the effective nuclear charge calculated from Slater's rules, n is the energy level of the electron being removed, and RH is the Rydberg constant. Depending on what units you want your ionization energy to be in will determine what value for the Rydberg constant you use. Most commonly electron volts (eV) is the energy unit used in which case the RH to be used is 13.6 eV. Kilojoules is also common in which case RH becomes 2.18 x 10^(-15) kJ.

Hope that helps.
• why is he unit of I.E in kilojoules/mole?
I.E is just a type of energy so shouldn't it be just joules or kilojoules?
why to find it for a mole?