What Happens when Stuff Dissolves?


What happens when stuff dissolves? I mean
like what happens to the atoms and molecules that make it up? I want to talk about two
things here you dissolve all the time, salt and sugar. These two things look very similar.
They’re both like kind of white powders made up of little grains and you can pour both
of them into water and stir around and you see the grains get smaller and smaller, maybe
break apart until eventually they’ve totally disappeared. They’ve completely dissolved
in the water, that’s what you see with the naked eye. But if you had atomic vision and
you could see the atoms that make up salt and sugar, what would it look like as these
grains broke apart and became invisible? That’s what we’re going to talk about here. So it
actually depends whether something is an ionic or covalent compound, it depends on what it
would look like when it dissolves. So over here we have salt and this is an ionic compound.
This is what a grain of salt would look like and it’s made up of Sodium ions (Na+) which
are metals and chloride ions (Cl) these blue things here which are nonmetals. So salt is
an ionic compound made of metals and nonmetals. Sugar on the other hand is a covalent compound
because it’s made of nonmetals: Carbon, Oxygen and Hydrogen and these nonmetal atoms are
connected together into a molecule. So a grain of sugar would look like this. It would be
a bunch of these sugar molecules all kind of lumped together. Notice that a grain of
sugar is a lot more messy, it’s not nearly as well organized as an ionic compound . . . this
grain of salt over here. Anyway, let’s look at what would happen when we dissolve these.
We’ll take a grain of salt, dip it in water and start stirring it around. With our atomic
vision, we’re going to see that the atoms that make up this salt are going to come apart
from each other. They’re going to break apart and they’re all going to start floating around
in the water individually. This is what it looks like when salt dissolves, okay? Now
let’s take our sugar. Here’s our grain of sugar, it goes in to the water, we stir it
around and the grain of sugar is going to break up like we saw the grain of salt break
up. But it’s going to break up in a different way. It’s going to break up into the individual
molecules that made it up. But these molecules are not going to break up into the individual
atoms, they’re going to stay as molecules and those molecules are going to start floating
around in the water. A big mistake that people make, I don’t want you to make this mistake,
is they think that when sugar or other covalent compounds dissolve, they think that the atoms
that make up the molecules totally break apart and then you end up with a glass of water
that has all these Carbon, Oxygen and Hydrogen just floating around. That does not happen,
big red X. Instead, the molecules stay together . . . the atoms in the molecule stay together.
So this is a big difference between how covalent compounds dissolve, where the molecules stay
molecules, and how ionic compounds dissolve where the grains of these things like salt
actually break apart into the individual atoms. So to answer the question, what does it look
like when something dissolves in water? The short answer is that it actually really depends
whether they’re talking about an ionic compound or a covalent compound. If it’s an ionic compound,
it’s going to break apart into all the individual atoms but if it’s a covalent compound the
clump of the molecules will break apart into individual molecules once it dissolves but
the molecules themselves will not break apart into atoms. They will stay as molecules dissolved
in the water.

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