Molecules

A molecule is an electrically neutral combination of two or more atoms of the same or different elements joined by covalent bonds.

I’m going to go ahead and break down this definition a little bit to make sure we really understand it. Notice up here it says that the molecule is electrically neutral.

Mini-test: MOLECULES 

Question 1: How are molecules charged?
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Question 2: Which of the following is a molecule?
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Next Lesson: Basic Properties of Gas

The transcript is provided for your convenience
That means it has no net charge, so any positive or negative charges in that molecule will cancel each other out so there’s no net charge, in other words, it’s neutral.

Now it’s a combination of two or more atoms. Now so this could look like this, two hydrogen atoms or one oxygen atom and one hydrogen atom together would work as well, because they have to be of the same, or different, elements, so either one of these works as a molecule. These are some simple examples of molecules and so molecules can be simple, like those right here or they can be as complex and large by a chemical macromolecule, such as proteins, starches, and cellulose.

Now proteins can range in size from 50 to more than 2000 amino acids linked by peptide bonds while starches and cellulose molecules can consist of more than 10,000 smaller glucose molecules covalently linked together. Now there are some substances out there, three in particular that I want to highlight that you may think are molecules, which actually are not classified as molecules, so I want to go over those.

One is aggregation of polar molecules, joined temporarily by hydrogen bonds. Another example is electrically charged ions joined by ionic bonds and then finally metals consisting of positively charged ions in a sea of delocalized electrons. These three substances that I just listed you may be inclined to classify it as molecules, but they actually are not, so I actually want to warn you about those.

Let’s just review the definition for molecules again as something that’s electrically neutral of two or more atoms of the same or different elements and they’re joined together by covalent bonds.  Remember all these things, they’re neutral, there has to be two, but there can also be more. Same elements or different elements and they have to be joined by covalent bonds.

Generally when you have a definition of something, usually a two-fold here, there are lots of different criteria, something has to be in order to be a molecule. You want to remember all these, see a substance, learn a little bit about it and be able to identify if it is indeed a molecule.

Next Lesson: Basic Properties of Gas