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Metallic solids

AP.Chem:
SAP‑5 (EU)
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SAP‑5.B (LO)
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SAP‑5.B.1 (EK)
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Metallic solids are composed of metal cations held together by a delocalized "sea" of valence electrons. Because their electrons are mobile, metallic solids are good conductors of heat and electricity. Metallic solids also tend to be malleable and ductile due to the ability of the metal nuclei to move past each other without disrupting the bonding. Created by Sal Khan.

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  • leaf green style avatar for user Eduardo Fasano
    Disclaimer - technical question, which might disorient some students that haven't read or watched the videos on the photoelectric effect (if so don't worry and maybe disregard this question)

    Question (much related to Lisa's) - Is the reason why metals are shiny have to do with the photoelectric effect, and the fact that these freer electrons floating around their metallic "electron seas" have low work functions, meaning that photoelectrons are more easily ejected thus making them shiny (i.e. amplitude of the photoelectrons?)
    (8 votes)
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  • mr pink red style avatar for user infinitely_isomeric
    If it is a sea of electrons in which cations are floating, the cations should repel each other being positively charged.Further, even the electrons should be repelling each other.
    Why does this not happen ?
    (6 votes)
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    • leaf red style avatar for user Richard
      You can think of a metallic solid similarly to an ionic solid where the positively charged particles are sandwiched in between the negatively charged particles. They alternate in a pattern so the positive charges are not in direct contact with each other, but are instead separated by negative charges. Same idea with the electrons, though they do experience repulsions from other electrons, the overall attractions to the metal cations around them are greater which keeps the solid in tact. Basically the overall forces of attraction are greater than the forces of repulsion in a metallic solid.

      Hope this helps.
      (3 votes)
  • mr pink red style avatar for user infinitely_isomeric
    Sal talked about there being a reason for the lustre of metals, but didnt actually explain it.
    Why do metals shine ?
    (4 votes)
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    • leaf red style avatar for user Richard
      The light which strikes the outermost electrons causes these electrons to oscillate since they are loosely held onto by the metal nuclei. This oscillation causes the electrons to produce their own light which is reflected back causing the appearance of what we would called luster. So essentially the luster of metals is due to the reflection of light shinning on them.

      However not all photons are reflected back, some small amount of photons manage to penetrate deeper and are absorbed. Different metallic elements have different ratios of reflection to absorption. Metals which appear more white have higher levels of reflection than metals which are grey and have engage in a bit more absorption.

      Hope that helps.
      (6 votes)
  • female robot ada style avatar for user Angelica Chen
    According to what I have learned, the transition metal palladium has two electrons that miss the proper subshell, and somehow ends up with 16 valence electrons (weird). How does this affect its resulting metallic solid structure, compared to other metals in its vicinity on the Periodic Table?
    (2 votes)
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    • leaf red style avatar for user Richard
      Well palladium's neutral electron configuration is unique in that it has a full 4d subshell leaving its 5s subshell empty. As far as forming a metallic solid this will effect things like its density.

      However for the 16 electron part you're referring to, that concerns coordination complexes. Coordination complex are somewhat like molecules, except the central atom is a transition metal atom. The bonds aren't covalent, rather coordination or dative bonds where the groups attached to the metal (called ligands) donate all the electrons for bonds instead of both atoms contributing electrons.

      For main group elements (groups 1&2, 13-18) they follow the octet rule which predicts how many electrons the atoms need to have to become stable. Transition metals follow a variation on this rule called the 18-electron rule where transition metals try to have 18 valence electrons in coordination complexes. Usually having 16 electrons is a sign of being electron deficient and the complex will be reactive in order to gain 2 more electrons, however metals like palladium and platinum aim to make 16 electron complexes. This causes a lot of these coordination complexes to adopt square planar structures instead of the more common octahedral structure of other coordination complexes.

      Hope that helps.
      (3 votes)

Video transcript

- [Instructor] Let's talk a little bit about metallic solids. And here is an example of what a metallic solid might look like. They tend to be shiny like this. Some would say lustrous. Some of you might be guessing maybe this is some type of aluminum or silver. It actually turns out that this is sodium. Our same friend sodium that we saw bonding with chlorine to form sodium chloride and form ionic solids, it can actually bond with itself with metallic bonds. This right over here, you might guess is silver or something. It actually turns out this is calcium. And I know what you're thinking. Isn't calcium kind of this chalky white powder? Well no, those are compounds formed with calcium, things like calcium oxide. But this right over here is pure calcium. And the reason why it has to be in this container, it is highly reactive with oxygen. So that's not oxygen that is in this container. It's some form of inert gas. But calcium when it just bonds to itself with metallic bonds, which we'll talk about in a little bit, it also looks kind of similar. It's this shiny, metallic, or lustrous look to it. And what do you think this is? Well this is something we're used to associating with metals, this is gold. But once again, you can see it has this lustrous property. So what is it about metals or metallic solids that allow them to be lustrous in this way and have other properties that we're about to see? And to understand that, we just have to look at the periodic table of elements. And that most of the periodic table of elements is actually some form of metal. You have in red right over here, this group one elements, not including hydrogen. Those are your alkali metals, and you have your alkaline earth metals, your transition metals, your post-transition metals, your metalloids. It's really only what you see in yellow and blue here that are not your metals. So how do metals form solids when you just have a pure sample of them? Well the general idea, you can look at your alkali metals, they all have that one valence electron. And to get to that stable outer shell, it's much easier for them to give away a valence electron. And that's why we often see these folks are dissipating in ionic bonds. They can be ionized quite easily. But if you have a pure sample of them, they can contribute electrons to a sea of electron, one each. These alkaline earth metals, they have two valence electrons. They too can be ionized or if you have a pure sample like in a calcium, they can contribute two valence electrons to a sea of electrons. And the transition metals here have a similar ability to contribute valence electrons. And so in general, we can view metallic solids as having cations, these positively charged cations in a sea of electrons. So you have all these electrons here. I'll just draw all these minus charges that they're in. Where do those electrons come from? Well if you're looking at the alkali metals, each of those atoms could give one electron to that sea because it doesn't really want that valence electron. If you're talking about alkaline earth metals, they could each donate two electrons to that sea. Now given that you have this positive charge in this sea of electrons, what are you think of the properties? How good do you think this will be at conducting electricity or heat? And many of you might guessed, if you looked at a wire, wires are made out of metals, because they are excellent at conducting electricity, or they tend to be excellent at conducting electricity, because you have all of these electrons that can move around. And so if you apply a voltage, they will start moving and conduct electricity. And those electrons can also be good at conducting thermal energy or heat. Now what would be, we already talked about them having the shiny, lustrous property, but how easy would it be to bend them? Ionic solids, we talked about they can be strong but brittle. As soon as you try to shift them around a little bit, they can break. But what do you think is going to happen here? If let's say right over here, I were to push really hard and on the top I would have pushed really hard to the left. Do you think this will be brittle? Or do you think it will be malleable? It's easy to bend. Well if you have a pure metallic solid, it's actually quite malleable. If you just took this top part and pushed it to the left like this, no big deal. You have those cations that are still in those that sea of electrons. And that's generally true of metallic solids. They're very malleable. They are not brittle. In fact, so much so that often times we want them to be a little bit more rigid. We want them to be a little bit harder. And that's why we might do things like add other elements into the metallic solid. For example, pure iron is reasonably malleable. But if you wanna make it stronger, you could stick carbon atoms in between. For example, you could put a carbon atom there, or carbon atom over there. And that way, it kind of disrupts this electron sea a little bit. So it's not quite as malleable. It'll be stronger and more rigid. So I'll leave you here. This is just an extension of what we've already learned about metals and metallic bonds. To just realize why most of the periodic table of elements that we're familiar with has some of these properties when they are, when you have pure solids of them.