Chemistry Archives - Page 19 of 22

20Aug 2014 by Vincent Summers 6 Comments

Cesium Auride – Relativistic Electrons?

Chemistry

[caption id="attachment_7305" align="alignright" width="440"] Imagine relativistic electrons.[/caption] Strange isn't the word for cesium auride. Gold in liquid form? Indeed, yes! Discovered more than a half century ago, the properties of this cesium and gold compound are not yet fully understood. There are all sorts of curios in chemistry. Chemists love them dearly. I still remember one particularly strange molecule. It was affectionately named hexamethyl bathroom tile. Free Lectures Recently I listened to some free online chemistry lectures. They were produced by MIT under its OpenCourseWare program. One of those lectures spoke of an alloy of cesium and gold that acts like a salt, cesium auride. Key to its forming is the difference in electronegativity between cesium and gold. It is roughly the same as the difference between sodium and iodine!…

24Jul 2014 by Vincent Summers No Comments

Acetylene and Acetylides

Chemistry

Acetylene and acetylides are easy to make and simple to understand. Acetylene (ethyne) is one of the tiniest organic compounds. Its formula is C₂H₂. The two carbon atoms share a triple bond. Its structure is HC≡CH. Acetylides are produced from acetylene by replacing one hydrogen atom. Acetylene is a useful fuel. Despite this, acetylene can form acetylides that are extremely dangerous, explosive! Making Acetylene Making the gas is simple. Mixing calcium carbide with water makes acetylene. CaC₂ + 2 H₂O → Ca(OH)₂ + C₂H₂↑ Calcium Carbide Where does calcium carbide come from? Lime and coke are combined at temperatures ranging from 2000 to 2100 degrees C in an electric arc furnace. CaO + 3C → CaC₂ + CO↑ [caption id="attachment_16272" align="alignright" width="280"] Calcium carbide[/caption] Triple Bond What is the origin of…

07May 2014 by Vincent Summers No Comments

The Iron Sandwich Compound Ferrocene

Chemistry

[caption id="attachment_6151" align="alignright" width="440"] Ferrocene - an Iron Sandwich Compound[/caption] Who doesn't love a ham and cheese sandwich? Or a peanut butter and jelly sandwich? Well, there are special chemical substances that resemble sandwiches. There is, for example, the sandwich compound ferrocene, (C₅H₅)₂Fe. It consists of an atom of iron "sandwiched" between two cyclopentadiene molecules. Sandwich Compound The classification of such metallic organic compounds is metallocene. D-orbital electrons in the iron atom add to the pi-electrons of two cyclopentadiene molecules. This stabilizes the structure, since the cyclopentadienyl anion (-1 charge) has aromatic properties. The iron atom adopts, in effect, a ferrous (+2) electrical charge. Other Metallocenes In general, metallocenes have mostly been of laboratory interest. Some do exhibit a marked level of importance. One application is in catalysis. Other metallocenes…

23Mar 2014 by Vincent Summers No Comments

The Quintessential Aromatic Hydrocarbon Benzene (Pt.3)

Chemistry

[caption id="attachment_18860" align="alignright" width="440"] Figure 1.[/caption] The aromatic hydrocarbon benzene, chemical formula C6H6, is the single most-often discussed of the aromatic hydrocarbons. It possesses the quintessential aromatic structure. How is that? It possesses the Hückel Rule correct number of 4n + 2 number π-electrons, for n = 1, and is flat. In addition, it meets all the other requirements for aromatic compounds. As an aromatic compound, its chemistry is considerably different than it would be if it existed as a mere cyclohexatriene isomer. We will discuss those differences in this, the third installment of our three-part article. Behavior of Hypothetical Cyclohexatriene Since cyclohexatriene would behave as if it were merely three conjugated1 double bonds, we would expect the compound to behave as any other alkene—rich in available electrons—only more so.…

23Mar 2014 by Vincent Summers No Comments

The Quintessential Aromatic Hydrocarbon Benzene (Pt.2)

Chemistry

[caption id="attachment_6069" align="alignright" width="440"] Benzene De-localized Pi-system - CCA Share Alike 3.0 Unported by Vladsinger[/caption] In Part One of The Quintessential Aromatic Hydrocarbon Benzene, we saw that the so-called 1,3,5-cyclohexatriene was really not completely described by the structure that that name implies. It is equivalent to 2,4,6-cyclohexatriene (if you flip the 1,3,5- structure over, and you get the 2,4,6- structure), and includes a variety of other contributing factors. Although we did not list them, they may include ionic contributors.1 In general, these are discounted. Visualizing Benzene's Structure The conclusion is that the compound actually has six equivalent bonds between adjacent carbon atoms, forming six internal angles angle each equal to 60°. The bonds are each, then, “single-and-one-half” bonds between each carbon pair. The molecule is flat, even as a collection…

23Mar 2014 by Vincent Summers No Comments

The Quintessential Aromatic Hydrocarbon Benzene (Pt.1)

Chemistry

[caption id="attachment_14959" align="alignright" width="440"] Cyclohexane - Chair Form[/caption] Benzene? What's that? Living creatures universally share an important characteristic: they all are constructed of carbon-containing compounds. For that reason, chemists call such compounds organic. Now the term organic has taken on additional meaning. Compounds that are similar, but not found in nature, are also called organic compounds. One group of organic compounds, whether found in nature or not, possess special properties—chemical and physical—that put them into a category apart. Once it was thought such compounds were distinguishable by smell or aroma. Each was labeled an aromatic, and—the property itself—aromaticity. Simple Hydrocarbons The simplest hydrocarbon1 is methane (CH4)—a gas. It possesses a tetrahedral structure, with a carbon atom at its center and four hydrogen atoms at the corners (See Figure 1). Since…

22Mar 2014 by Vincent Summers 14 Comments

Why Sulfuric Acid Turns Sugar Black

Chemistry

Sugar is white. Sulfuric acid is colorless. So how is it sulfuric acid turns sugar black? Table sugar is actually two sugars in one—a disaccharide. It is commonly known as sucrose. Sucrose is a combination of fructose, a sugar found in fruits, and glucose, known also as blood-sugar, grape-sugar, and corn-sugar. Its chemical formula is C₁₂H₂₂O₁₁. The way these atoms are attached to each other by chemical bonds determines its structural formula. In the Left Corner… Most sugar from a grocery store is granular and pure white. If the grains are large enough—existing as large crystals—it is immediately apparent that sugar isn't even white; it is totally colorless and transparent. Sold at candy stores, we call it rock candy. [sc name="MidArticleAdsense"] In the Right Corner… Concentrated sulfuric acid is thick…

22Mar 2014 by Vincent Summers 1 Comment

Chopping Onions Makes You Cry

Chemistry, Food

[caption id="attachment_17235" align="alignright" width="480"] Purple onion.[/caption] You are about to prepare a delicious meal—a meal that requires you to slice or chop onions. Do you dread the task? The act of chopping onions is simple enough, but you know already chopping onions makes you cry. Why? What can you do to avoid it? Let's find out. Chopping Onions Makes You Cry The chemical that comes from preparing onions is called a lachrymator. That word lachrymator is simply defined as a chemical that irritates the eyes, causing tears to flow. In fact, a purely gaseous lachrymator may be called "tear-gas." Yes, onions produce tear-gas: specifically, (Z)-propanethial-S-oxide (PTSO). Onions of themselves don’t cause a problem. It is the slicing and chopping of them, the damage inflicted to the cell walls, that causes…

22Mar 2014 by Vincent Summers No Comments

What are Allotropes?

Chemistry

[caption id="attachment_6012" align="alignright" width="440"] Cyclooctasulfur (S8)[/caption] What are allotropes? An allotrope is one of a variety of forms in which an element can exist. This does not refer to the state of an element, whether solid, liquid, gas, or plasma. It refers to the tendency of an element to exist in different structural forms. Allotropes of Carbon Thus carbon can be found in a variety of forms, including graphite, charcoal, diamond, fullerenes, and nanotubes. Of Sulfur Sulfur allotropes take an assortment of forms. These include rings that range from six to twenty atoms. Especially well known are the monoclinic and rhombic crystalline forms. Of Phosphorous Phosphorus allotropes exist in a variety of colors. Ordinary phosphorous is called white phosphorous (P₄). It is unstable and dangerous. But there are also red,…

21Mar 2014 by Vincent Summers 2 Comments

The Aromatic Cyclopentadienyl Anion

Chemistry, Education

[caption id="attachment_16480" align="alignright" width="440"] Cyclopentadienyl Anion[/caption] Is it possible that for an ion to be aromatic? Yes. Consider the aromatic cyclopentadienyl anion. Hückel’s Rule dictates a flat ring with 4n + 2 π (pi) conjugated electrons. The smallest neutral ring with these qualifications has n = 1. It is benzene (C₆H₆). But Hückel’s law does not require an electronically neutral structure. The smallest aromatic ion is the cyclopropenyl cation¹ (C₃H₃⁺). Is there a negative ion that has 6 π electrons and is aromatic? The answer is yes. The aromatic cyclopentadienyl anion (C₅H₅⁻). Neutral Cyclopentadiene Neutral cyclopentadiene is flat. It is pentagon shaped. Three of the carbon-carbon bonds are single bonds. The other two are double bonds. At each of the four ends of the two double bonds there is one…