When it comes to chemistry, we may all be cerebral hemophiliacs. It sounds like you are a person that wants to know why rather than how. I have an Uncle with an 8th grade education that “doesn’t think book lernin has any use in the real world. He crawls over old cave ins in our family gold mine with his fanny scraping the ceiling. He knows dozens of assay proceedures step by step without a clue as to why.
I was going to recommend a copy of the possession I have owed longer than anything else I have: The Golden Book of Chemistry Experiments. However, it has been out of print for over 40 years and sells at Amazon.com for $187.50 It still wouldn’t give you everything you want to know. Instead, I will make a few recommendations in order of what I think is important then give you some basic chemistry facts.
Cheap and easy: Barcharts.com look under periodic chart and chemistry. The periodic chart is inexpensive and essential no matter what level of chemistry in which your are intrested. When I purchased mine, they were only 3 or 4 dollars apiece.
Basic nomenclature and practical Get a college general chemistry lab book (not text)…it lists various ions and naming conventions like the difference between sulfide, sulfite, and sulfate. Solubility of ions is important and should be included too. The chemsitry text books are not nearly as specific about properties as the lab book. Good lab books are by no means just comprised of experimental proceedures. They don’t have much about theory but are full of the kind of stuff that you encounter when reading about chemistry as it applies to jewelry making. They are usually quite a bit less expensive than text books.
Good reference: McGraw-Hill Dictionary of Chemical Terms available thru Amazon.com starting used at about $12.00
Try a high school chemistry book.
To get more specific (but more expensive) about chemistry as it applies to jewelry get The Theory & Practice of Goldsmithing by Professor Doctor Erhard Brepohl translated by Charles Lewton-Brain. It includes chemistry, physics, engineering and far more. It is more technically comprehensive about our field that any I have found so far. Available thru Rio Grande.
Finally, if the purchase of gold, gemstones and exotic tools has not emptied your savings account, you can purchase the Merck Index. It is an essential reference for chemists, giving physical properties such as density, melting point, solubilities, etc for over 4,000 chemicals.
Now for a couple of essentials about theory; remember, our brains are not really capable of directly knowing what really happens on the electronic or atomic level. The best we can do is build models that explain things well enough that we begin to be able to predict what will happen. As we learn more, our models change. Usually just a little but sometimes dramatically. The model I am presenting here is simplified:
First chemistry is about the interaction of electrons. Attraction between electrons is what holds atoms together. Attraction between negative charges you say? I thought negative charges repel one another. Yes, they do. But electrons spin giving them a magnetic field with north and south pole at the axis of spin. Electrons merely need to align with one another such that north pole is close to south pole to achieve a magnetic attraction for one another. You can think of an electronic bond like the ping-pong ball balanced in the air stream of a vacuum cleaner exhaust hose. Lifted up by the air but pulled down by gravity. The ball remains balanced between the two forces. This magnetic attraction is so powerful that in our everyday environment, electrons are unable to remain unpaired for more than a fraction of a second. (we will skip plasmas)
Now that we know that electrons are attracted into pairs, we need to discuss how they are arranged around the positive nucleus of the atom. Electron pairs have no attraction to one another. The strong negative charge of the pair repels other pairs while being attracted to the positive nucleus. Think of the nucleus as the baggage claim area at the airport. Everybody (electron pairs) wants to get up close until there is no more room at the conveyor (nucleus). Then a second tier of passengers begins to form behind the first tier. Think of these tiers as electron orbitals. When there are only a few waiting passengers, they have a lot of room so don’t really need to compete to stand so close. When the tier is nearly full, they all need to stand close to keep their spot. The competition of electron pairs for the positive nucleus draws them in very close as the orbital fills with electrons.
Now that we know about the forces that cause electron pairs and the forces that draw electrons to the nucleus, can talk about how they pair into two types of chemical bonds: Ionic and Covalent. Ionic bonds form when an element at the far left with only one or two electrons drifting in large orbits around a nucleus find that they can get much closer to a nucleus by attending to one of the compact crowded atoms with just a little space remaining in the orbital (far right of the periodic chart).
The ionic bond results in some atoms with more electrons than protons and some with less. These ions have a positive or negative charge. Since positives and negatives attract, positive atoms are attracted to whatever around them has a negative charge.
Closer the the center of the chart electrons with unfilled orbitals don’t have such a strong preference as to which atom go with. You might say they switch back and forth in complicated molecular orbitals. All this switching keeps the parent atoms involved with one another rather than interested in whatever opposite charge that comes along. These are called covalent bonds.
Borderline cases are called polar covalent bonds; the atoms stay together but one or more pair of electrons stay closer to one atom than the other. The most important polar bonded substance is water. The negative oxygen can attract positive ions while the more positive hydrogen can attract negative ions. This is what allows ionic substances to dissolve in water. Examples: Sodium chloride, calcium chloride, potassium hydroxide etc. (your lab book will list important ions.) Metals typically form positive ions if they can find some source to impart a positive charge such as the positive hydrogen in acids. Some metals form positive ions easier than others. (we won’t get into the electromotive chart except to say that it can give you a clue as to how easy and what it takes to give a metal a positive charge so it will dissolve in water.)
Think of an ionic solution as a soup of all the different ions that are dissolved in it. The ions drift around not caring which opposite charge they are affiliated with at the moment. As you evaporate the water out, the atoms will pick an opposite to settle down with but are not too picky as to which. If you dissolved some sodium chloride in water along with some potassium iodide, then evaporated the water, you would get some sodium chloride, some potassium chloride, some sodium iodide, and some potassium iodide.
So how do we sort thing out in an ionic solution? There is a thing called a double replacement reaction that can get various ions together. There are three things that can get one ion to form a lasting relationship with another ion. (I feel like I am beginning to sound like a marriage counseler)
First is formation of a gas that passes out of the liquid. Hydrogen chloride is a gas that when dissolved in water forms hydrochloric acid. H+ and Cl- wandering around in the water. Now if you were to put some Sparex in the water with some table salt, you would have a soup that contained some H+, some Cl-, some Na+ and some SO4- plus perhaps a little HSO4-. (The signs on the end indicate charge) I would expect you to get a little of the pungent smell of hydrogen chloride evaporating out of the solution. Given a perfect ratio of ingredients, you would eventually be left with a solution containing only sodium sulfate.
The second thing that drives a double replacement reaction is formation of a precipatate. Here is where the solubility rules from a college lab book are important. For instance, there are three chlorides that are insoluble in water. Lead chloride, mercury chloride, and silver chloride. Say you had a solution of silver nitrate and added some table salt (sodium chloride) Silver chloride would precipatate out leaving you with sodium nitrate in solution.
The third thing is formation of a covalent bond. The classic example is the reaction of an acid with a base to form water plus a salt. HCl plus NaOH (hydrochloric acid plus sodium hydroxide also known as lye) form H20 (water) plus NaCl, table salt.
The final thing I have time left to write about this morning is more about polar bonds as related to weak acids and bases. Strong acids and bases are ionic substances that undergo nearly complete dissociation in water. That is they dissolve completely into constituent ions. Weak acids and bases are polar covalent substances that will dissociate into ions if the attraction is strong enough. Vinegar is an example. As it dissolves in water, there is more and more competition for the polar sites on the water molecule. As the competition increases, the incentive to dissociate decreases. It ends up partially in the covalent state and partially in the ionic state. Various weak acids have various ability to dissociate in water. I expect that Sparex would be stronger that vinegar because it is fairly easy to tempt the hydrogen from the sulfate.
The chemistry of solutions is probably the most important thing for you to learn as far as applying chemistry to our craft. Hopefully this helps. If you have additional questions in your readings, contact me off of Orchid. While I am not a professional chemist, I do remember a little from my college days.
Howard Woods In the beautiful foothills near Eagle Idaho
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