Periodic Trend: Electron Affinity - Online Tutor, Practice Problems & Exam Prep

Electron affinity (EA) is the energy released, typically measured in kilojoules, during the exothermic process of adding an electron to a gaseous atom or ion, resulting in a more negative species. A higher negative value of electron affinity indicates a stronger tendency to gain an electron. As we move across the periodic table towards the top right corner, electron affinity generally becomes more negative, signifying an increase in exothermicity. However, there are exceptions where elements have electron affinities that are zero or positive, indicating a reluctance to accept electrons. This reluctance is due to the stability provided by completely filled or half-filled orbitals, as seen in elements like beryllium, nitrogen, and noble gases. Elements like zinc, which have a completely filled d subshell, also exhibit this behavior. Understanding electron affinity is crucial as it influences how elements form chemical bonds and react with one another.

Periodic Trend: Electron Affinity

Here we're saying that electron affinity, abbreviated as EA, is the energy released, making it exothermic from the addition of an electron to a gaseous atom, or ion in kilojoules. Now you may also get it in kilojoules per mole, but for the most part we're going to say it's in just in kilojoules. Now we're going to say here we're talking about adding an electron to an atom or an ion.

So here we have neutral carbon, we're going to add an electron to it. So here is the electron we're adding. When it gains that electron, it becomes more negative. So now it's going to be C^- as a gas. Now here this is an exothermic reaction. So in an exothermic reaction, we release energy in order to create a bond. Releasing energy means that we're going to have a negative sign for electron affinity.

Now we're going to say here that the more negative the electron affinity value is, then the more exothermic the reaction becomes. And we're going to say here that there are exceptions. When we look at the periodic table in the next video, there are exceptions to electron affinity. For the exceptions, we're going to say that they are equal to or greater than 0, and that means the element will not readily accept an electron.

So if your electron affinity is 0 or higher, that means that element does not want to accept or it cannot accommodate an electron because it interrupts their stability. So now that we've talked about electron affinity, click on to the next video and let's take a look at the periodic table.

Periodic Trend: Electron Affinity

So if we look at the periodic table, we see that for electron affinity, we're going to say that it becomes more exothermic. So we can say that it increases as we move to the top right corner of the periodic table. So notice here we have -72.8 for hydrogen and we have -328 for fluorine. Remember, the more negative your electron affinity, the more exothermic the reaction. That means it wants the electron even more. So we can see that fluorine wants an electron even more than hydrogen.

If we go down, we can see here that cesium is -45.5, so it doesn't as readily want an electron. Also notice here that the bottom row does not have any values. Those elements are so large, so unstable, that we tend not to talk about their electron affinity. You'll also notice that certain elements are have electronic affinities that are equal to or greater than 0. So we have beryllium here, we have nitrogen. We have the noble gas, which makes sense because they're perfect. So they don't require accepting an electron, they don't need it.

Some others are not, as commonly seen. Here we have manganese, we have zinc, cadmium, and mercury, and we'll see why those are less than 0 or not less than 0, equal to or greater than 0. Then we have HF over here in yellow. That's because it's a weird element. There's no real solid like justification for why it's greater than or equal to 0 is just one of those auto elements out there. But for all the ones that are in Aqua, we'll see the justification of why they have electron affinities that are greater than or equal to 0.

Periodic Trend: Electron Affinity Example 1

Here are the example question says which of the following halogens will have the most exothermic electron affinity. So remember your halogens are the elements in Group 7A of the periodic table. So if we look at the choices sulfur, neon, nitrogen, acetene and bromine, only two of them exist as halogens and those would be options D&E.

So now we have to think about who has the more exothermic electron affinity which means it's more negative. Remember as we head to the top right corner, our electron affinity increases, meaning it becomes more exothermic. So here bromine is higher up in Group 7A, so bromine would have the more exothermic electron affinity.

Now know it's a little weird. More exothermic really means it's a more negative value. But just remember, when we're talking about greatest electron affinity, we're talking about most exothermic.

Periodic Trend: Electron Affinity

So let's talk about the exceptions to electron affinity. So the exceptions are elements that possess stable or symmetrical orbitals and they're less likely to accept an electron. Now remember S subshell orbitals are most stable when they are totally filled with electrons. So here if we looked beryllium was one of our exceptions, its S orbital is completely filled in, therefore it doesn't want to accept another electron. So that's why it's electron Infinity is greater than or equal to 0.

Then remember that P&D sub shell orbitals are most stable when they're half filled or totally filled. Looking at nitrogen, its P orbitals are half filled, therefore it doesn't want to disrupt that stability, so it doesn't want to accept an electron. Manganese, it's D orbitals are half filled with electrons, so it two does want to accept an electron, then finally zinc. In those below it, they have a totally filled in D set of D orbitals, so zinc in the ones below it in terms of the periodic table wouldn't want to accept another electron.

All of these are stable the way they are, they all have either half filled or totally filled PDORS orbitals. So just keep that in mind when you see these exceptions to electron affinity in terms of the chart. And remember, for the most part, as we head to the top right corner, electron affinity becomes more exothermic.

Which of the following represents the third electron affinity of Si?

• A.
• B.
• C.
• D.

Determine which atom in the following set has the most exothermic electron affinity:N, O, C, B, Ne

• A. N
• B. O
• C. C
• D. B
• E. Ne

Rank the following elements in order of increasing electron affinity: Cs, Hg, F, S

• A. Hg < S < F < Cs
• B. Hg < F < S < Cs
• C. Cs < S < F < Hg
• D. Hg < Cs < S < F
• E. Cs < Hg < S < F

Here’s what students ask on this topic:

What is electron affinity?

Electron affinity refers to the amount of energy released when an electron is added to a neutral atom in the gaseous state to form a negative ion. It's a measure of the tendency of an atom to accept an electron. This property is important because it gives insight into the reactivity of different elements, particularly nonmetals, which generally have higher electron affinities.

When an electron is added to an atom, energy can either be released or absorbed. If energy is released, the electron affinity is positive, indicating that the atom readily accepts an electron. Conversely, if energy is absorbed, the electron affinity is considered negative, suggesting that the atom is less inclined to gain an electron.

Electron affinity can be influenced by several factors, including the atomic structure of the element and the effective nuclear charge—the net charge an electron experiences from the nucleus, taking into account the shielding effect of electrons in inner shells. Elements with a higher effective nuclear charge typically have greater electron affinities.

Why does electron affinity decrease down a group?

Electron affinity refers to the amount of energy released when an electron is added to a neutral atom in the gaseous state to form a negative ion. As you move down a group in the periodic table, the electron affinity generally decreases due to several factors.

Firstly, as you go down a group, the atomic size increases because additional electron shells are being added. This means that the added electron is further away from the nucleus, which lessens the attractive force exerted by the positively charged nucleus on the negative electron.

Secondly, there is an increase in electron shielding with each added electron shell. The inner shells of electrons act as a shield between the nucleus and the valence shell where the new electron is being added, reducing the effective nuclear charge felt by the added electron.

Because of these factors, the energy released when an electron is added to an atom lower in a group is typically less than that for an atom higher up in the same group, indicating a decrease in electron affinity.

Why does electron affinity increase across a period?

Electron affinity generally increases across a period on the periodic table due to the effective nuclear charge experienced by the electrons. As you move from left to right across a period, the number of protons in the nucleus increases, which in turn increases the nuclear charge. However, the additional electrons are being added to the same energy level and do not significantly increase the shielding effect. This means that the effective nuclear charge felt by the outermost electrons becomes stronger.

As a result, the attraction between the nucleus and the added electron becomes greater, making it more energetically favorable for the atom to gain an electron. This increased attraction leads to a higher electron affinity, meaning that atoms will release more energy when they gain an electron. However, there are exceptions to this trend, particularly when filled or half-filled subshells provide extra stability to the atom, which can affect its willingness to accept additional electrons.