AS1205D CHM 361 | CRYSTALLINE SOLID - VIDEO PRESENTATION

[00:00:00]Assalamualaikum and hi everyone. In this video, we will present about crystalline [music] solid.

[00:00:08]Before we begin, let us introduce our team members. The first member is Nur [music] Alisa binti Khairunizam. The second is Nurul Izzati binti Muhammad Arif. The third is [music] Nurul Anis binti Azmi. And lastly, my name is Nur Shahada binti Abu Manap. And together with my [music] team, we prepared this presentation.

[00:00:33]Have you ever wondered why some solids have perfectly ordered structure while others [music] don't? Today, we are going to answer that question. Our presentation [music] has three main objectives. First, we'll compare crystalline and amorphous solid and see [music] what makes them different. Next, we'll explore stoichiometric and non-stoichiometric defects, which are imperfections found [music] in crystal structure.

[00:01:03]Lastly, we learn about the F center in NaCl an interesting defect where [music] a missing chloride ion traps an electron causing the crystal to develop develop colors.

[00:01:17]A crystalline solid [music] is a material in which atoms, ions, or molecules are arranged in a highly ordered and repeating [music] pattern.

[00:01:25]Because of this regular arrangement, crystalline solids have a sharp melting point and [music] a definite heat of fusion. Another important characteristic is that they are anisotropic, meaning their physical properties, such [music] as electrical conductivity or strength, may vary depending on the direction.

[00:01:44]Common [music] examples include diamond, quartz, and sodium chloride. Unlike crystalline [music] solids, amorphous solids do not have a regular arrangement of particles. Their atoms are randomly arranged [music] giving them a disordered structure. As a result, they do not melt at one specific temperature, but instead soften over a range of temperatures.

[00:02:07]They are isotropic, meaning their properties remain the same in all directions.

[00:02:13]Examples include glass, plastic, [music] and gels.

[00:02:16]>> So, have you ever wondered why some metals are easily bent and the others [music] are harder?

[00:02:22]The answer is it depends on their crystal structure.

[00:02:25]Let's understand their crystal structure first. [music] There are three common structures, that is body-centered cubic, which is BCC, >> [music] >> face-centered cubic, FCC, and hexagonal close-packed, HCP. First, BCC have eight corners atom and one atom at the center. This structure make materials [music] strong and hard, but less ductile. For example, iron, chromium, and tungsten. Next, for FCC, atoms located at the corner and the face of each cube. Since the atom packed more closely, FCC material is more ductile and easy to shape. For example, [music] aluminum, gold, and silver. HCP has hexagonal arrangement with close-packed atoms. It provides high [music] strength, but less ductile than FCC. Example is magnesium, titanium, and zinc.

[00:03:20]>> And now, [music] I will explain to you about stoichiometric defects.

[00:03:24]Stoichiometric defects are a specific type of crystal imperfection. [music] The word stoichiometric means that even though there are mistakes in the structure, the balance and ratio between the cations and anions [music] in the atom remain exactly the same.

[00:03:40]Stoichiometric defects [music] generally happen in one of four ways.

[00:03:45]The first one is vacancy defect. [music] It is where an atom is missing completely from its assigned spot. Next, interstitial defect. [music] It happened when an extra atom squeezes into an empty space where it does not belong. The third one is [music] Schottky defect. A matching pair of one positive and one negative ion go missing together at the same [music] time. The last one is Frenkel defect where an ion gets misplaced, leaving its original spot empty and crowding into a nearby [music] gap.

[00:04:21]These defects occur in two different conditions, where vacancy [music] and interstitial occurs in non-ionic crystal, or Frenkel and Schottky happens in an ionic crystal.

[00:04:34]Stoichiometry defects give materials their [music] useful properties.

[00:04:39]In vacancy defect, the density drops.

[00:04:42]This give the remaining atoms room to hop around, >> [music] >> enabling the solid-state diffusion needed to harden metals. In interstitial defect, [music] an atomic traffic jam that occurs block internal movement, becoming the reason why steel [music] is harder than pure iron.

[00:05:01]In Schottky defects, the missing pairs leave [music] behind open pathways that allows ions to migrate.

[00:05:09]>> [music] >> This high ionic conductivity is the exact principle behind a solid-state batteries.

[00:05:16]In Frenkel [music] defects, there is no mass loss and density stays the same, but that displaced ion is [music] now highly mobile. This ion mobility is the exact mechanism that drive drives traditional film photography. While none of these defects alter a material's chemical formula, [music] they completely change how it behaves.

[00:05:40]And density changes tell us exactly [music] why it's happening in the atomic level.

[00:05:49]Now, >> [music] >> let's move on to the non-stoichiometric defect. Unlike stoichiometric [music] defect where the ratio of cation and anion remains balanced, [music] non-stoichiometric defect happen when this ratio is no longer equal. In other word, [music] the number of positive and negative ions is different. There are two main type of [music] non-stoichiometric defect. First is metal excess.

[00:06:15]As the name suggests, the crystal [music] contains more metal ions than expected. This usually happen because the defect >> [music] >> such as missing anions or extra metal ions in the crystal. The second type [music] is metal deficiency where it's opposite situation, some positive metal ion are missing [music] from the crystal lattice. Even though ions are missing, the crystal [music] still maintains electrical neutrality by changing the oxidation state of some of the remaining metal ions. So, a simple way to remember it by [music] metal excess equal to too many metal ion and metal deficiency equal to not enough metal [music] ions. Let's look at those two in detail.

[00:07:02]Starting [music] with metal excess defect, as mentioned earlier, there are more [music] metal ions than normal. One common cause is when an anion is missing from the lattice.

[00:07:16]The empty [music] space doesn't stay empty. It trap the electron forming what we call F S F center.

[00:07:23]>> [music] >> The letter F come from German word Farbe meaning color.

[00:07:29]This trapped electron [music] absorbs a co- certain wavelength of light giving the crystal its characteristic color.

[00:07:35][music] For example, NaCl, KCl, LiCl can develop color when they contain F centers. [music] Normally, pure sodium chloride is colorless, but with this defect, it may appear [music] yellow.

[00:07:49]Now, let's move to metal deficiency [music] defect. Here, some positive metal ion are missing from the crystal lattice. To keep the overall charge balance, some metal ions [music] change to a higher oxidation state, which is why this compound often show [music] variable valency. For example, NiO, FeO, [music] and FeS.

[00:08:14]If you look at this diagram, you can see a missing [music] metal ion called vacancy. Around that vacancy, some ion change their charge [music] to compensate for the missing positive ion.

[00:08:27]So, the key difference is [music] metal excess have extra metal ion or trapped electron, produce F-center and color.

[00:08:35]>> [music] >> Metal deficiency uh have missing metal ion compensate by variable oxidation [music] state.

[00:08:42]>> This is a comparison between stoichiometric and non-stoichiometric defects. Stoichiometric defect does not affect the chemical [music] formula.

[00:08:51]Non-stoichiometric defect change the compositions. Stoichiometric defect include vacancy, interstitial, Schottky, and Frenkel defect.

[00:09:04]Meanwhile, non-stoichiometric [music] defects include metal excess and metal deficiency. This comparison have us classify this defect easily.

[00:09:14]>> This slide explains [music] why pure sodium chloride is white, but defective sodium chloride becomes yellow. [music] In pure sodium chloride, all sodium and chloride ions occupy [music] their correct lattice positions, so visible light is not absorbed. However, when sodium chloride is heated in sodium vapor or exposed [music] to radiation, some chloride ions leave their lattice positions. The empty sites trap electrons and forming the F centers.

[00:09:42]>> [music] >> The trapped electrons absorb certain wavelengths of visible light. As a result, [music] the remaining reflected light gives the crystal a yellow color.

[00:09:52]>> For the conclusion, crystalline solids are important to inorganic chemistry because of their ordered [music] atomic structures, which give them predictable and unique properties. Their study effectively bridges the gap between microscopic atomic [music] arrangement and real-world material behavior. While perfect crystals exist only in theory, the real value of crystalline materials lies in our ability to understand, control, and apply both their structures [music] and their inherent imperfections.

[00:10:27]Crystalline solids are everywhere, making them truly indispensable to both science and our everyday life.

[00:10:36]>> These are the references [music] we used to prepare this presentation. We referred to reliable journal articles and academic resource to ensure [music] the information is accurate and up-to-date.

[00:10:49]>> That is all for our presentation, crystalline [music] solid. Thank you and assalamualaikum.