Periodic table base definition chemistry4/14/2024 ![]() Finally, many organic reactions are catalyzed by acids and/or bases, and although such transformations may seem complex, our understanding of how they occur often begins with the functioning of the catalyst. Second, some classes of organic compounds have distinctly acidic properties, and some other classes behave as bases, so we need to identify these aspects of their chemistry. First, acid-base reactions are among the simplest to recognize and understand. It is useful to begin a discussion of organic chemical reactions with a review of acid-base chemistry and terminology for several reasons. If there are a lot of OH - ions compared to the number of H + ions, the pH is high.Acids & Bases Acidity and Basicity Brønsted If there are a lot of H + ions, the pH is very low. That pH scale we talked about is actually a measure of the number of H + ions in a solution. There are other ions that make acidic and basic solutions, but we won't be talking about them here. ![]() An example of a strong base is sodium hydroxide (NaOH). If one of the ions is OH -, the solution is basic. The strong acid hydrogen chloride (HCl) is one example. If one of those ions is H +, the solution is acidic. If you have an ionic/electrovalent compound and you put it in water, it will break apart into two ions. We'll talk about baking soda in a few paragraphs. Remember that acetic acid example? Bases are compounds that break up into hydroxide (OH -) ions and another compound when placed in an aqueous solution. Acids are compounds that dissociate (break) into hydrogen (H+) ions and another compound when placed in an aqueous solution. Let's look at the breakup of molecules in aqueous (water-based) solutions one more time for good measure. What really happens in those solutions? It gets a little tricky here. Overall, Lewis' definition was able to classify even more compounds as acids or bases. ![]() Hydrogen ions still want to accept two electrons to form a bond. We know that both of these descriptions of acids and bases use completely opposite terms, but the idea is the same. In Lewis' view, acids accept pairs of electrons and bases donate pairs of electrons. Instead of looking at hydrogen ions, he looked at pairs of electrons (remember our pictures with dot structures in Atoms and Elements?). Does that mean the water was the acid in this situation? Yes.Ī chemist named Lewis offered a third way to look at acids and bases. If it got the H+ from a water molecule, then the water (H 2O) was the proton donor. You didn't have to worry about hydroxide ions anymore. Since bases are proton acceptors, when ammonia was seen accepting an H+ and creating an ammonium ion (NH 4 +), it could be labeled as a base. Scientists used the new definition to describe more bases, such as ammonia (NH 3). This newer definition is a little bit more detailed. It's a lot like the first definition we gave, where an acid breaks up and releases/donates a hydrogen ion. What were they donating and accepting? Hydrogen ions. These two chemists from Denmark and England looked at acids as donors and bases as acceptors. You're also going to learn about Brønsted-Lowry ideas. We told you about that guy Arrhenius and his ideas about concentrations of hydrogen and hydroxide ions. Weak bases usually have a pH close to 7 (8-10). This means that not every molecule breaks apart. Weak Base: A base that only partially ionizes in an aqueous solution. Weak acids usually have a pH close to 7 (3-6). Weak Acid: An acid that only partially ionizes in an aqueous solution. Strong Base: A base that has a very high pH (10-14). Strong Acid: An acid that has a very low pH (0-4). Another word for base is alkali.Īqueous: A solution that is mainly water. It comes from the Latin word acidus, which means "sharp" or "sour".īase: A solution that has an excess of OH - ions. Here are a couple of definitions you should know:Īcid: A solution that has an excess of H + ions. There is a scale for acids and bases just like everything else.
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