In the last post, we discussed monatomic and polyatomic ions. In this post, we will go over binary molecular compounds, which is a fairly simple topic of study, with a few rules to follow. A binary compound, as the name implies, is a compound that is composed of two elements. Binary compounds can be separated into two groups, according to Ebbing and Gammon in their 2009 textbook.
When writing the formula for a compound, there are also conventions to follow, dictating the order in which the elements are placed. The order that elements in the formula must follow is as given below, by Ebbing and Gammon:
Element: B Si C Sb As P N H Te Se S I Br Cl O F
You might notice, from this, that these elements actually follow somewhat of a pattern of increasing group number, with B from Group IIIA, Si and C from Group IVA, elements Sb to N in Group VA, H not included, elements Te to S in Group VIA, elements I to Cl in Group VIIA, O not included, and F not included (Ebbing and Gammon 2009).
If you noticed this trend, what this tells you is that you can find out the order that elements in a binary compound should be written in, easily, using a periodic table of elements, which you will almost always have available to you when studying chemistry or taking an exam in the course. Specifically, this order goes from decreasing to increasing nonmetallic character. So, the elements in the beginning are more metallic than those further down the line (Ebbing and Gammon 2009).
Now, on to the rules for naming binary molecular compounds. Yes, more rules, also given to us by Ebbing and Gammon:
There are some things to consider, however. There are random oddities of the naming system that you should be well aware of, per Ebbing and Gammon:
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