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Ionic Compound Properties 21,947 views

Teacher/Instructor Kendal Orenstein
Kendal Orenstein

Rutger's University
M.Ed., Columbia Teachers College

Kendal founded an academic coaching company in Washington D.C. and teaches in local area schools. In her spare time she loves to explore new places.

Ionic compound properties stem from their structure. Ionic compounds are found in lattice structures, making them extremely brittle. Ionic compounds have high melting points and form electrolytic solutions, which conduct electricity. Covalent compounds, on the other hand, are comparatively soft and round, have relatively low melting and boiling points and form non-electrolytic solutions.

We're going to talk about properties of ionic bonds or ionic compounds versus the properties of covalent bonds or covalent compounds. So we know ionic compounds we're going to call them formula units because ionic compounds are actually a ratio of ions. Ions being charged particles, held together in crystal structure. So they're not actually like individual like you can't have, like if you have a salt molecule or salt compound for example, you can't have just have one Na and one Cl there's actually going to be a ratio of Na plus ions and Cl minus ions. We're going to call the structures ionic crystals or lattice crystals and we're going to call one unit, we're going to call that a formula unit. So if you've seen that in class, that's what that means there's just a ratio, the lowest ratio of ions.

Okay so ionic compounds are composed of metals which are cations or positively charged particles and non-metals which are anions and negatively charged particles and that they're held together they actually create what they call salts. So anytime you hear the word salt is not necessarily table salt it could be any type of ionic compound. Alright so ionic compounds when they're held together they actually form something very rigid. This is an example of ionic compound, it is noticed that they are rigid, it's hard, it's very hard and brittle to the touch so and they're very sharp. So ionic compounds can actually like, actually they can hurt you if you like rub around in your hands and actually could have this like hard kind of point feeling to it.

Okay also their boiling points and melting, sorry the melting points and boiling points are really, really high because basically all they are two ions held together. For example table salt has a meting point of 801 degrees Celsius like it's ridiculously high, you've never actually melted salt before there's just too much heat is required, too much energy is required to break apart this ions to make it melt or to make it melt or to make it actually like a gaseous compound. The reason so, the energy that it takes has actually broken down into Coulomb's law. Coulomb's law explains that Mathematically and so the force that's held together that's the f this is our constant which is a Coulomb's constant and then this two represent the charges multiplied together divided by the radius of the two ions squared. So the bigger the compound and the smaller the ratio or the smaller the charges the actual easier it is for it to break apart and melt. So for example if you're comparing cesium bromide versus calcium oxide cesium bromide has let me make this darker plus 1 minus 1 charge. So these guys have very low charges multiplied together and these guys are big ions.

They're pretty big, so that's going to take not much energy for them to break apart, however calcium is a plus 2, oxygen is a minus 2 and they're smaller in comparison so they're actually have a much higher, they're much more. The force that's holding them together is much greater so actually they're not going to, they're actually going to take a lot of energy to melt that one. If we compare it to covalent compounds well we're going to call them molecules they're actually soft and round, so if we were to look at a picture of a covalent compound, this is sugar notice that it is softer edges, it's much more smooth to the touch there's no hard spots or pointy spots that you can actually like hurt, it's very soft, it's very, so yeah, so it's much more smooth comparatively. So when you have, when covalent compounds come together we're going to call those things molecules, they're different because you can actually have one molecule in your hand versus ionic compound you can't. So they are composed of two or more non-metals, so non-metals only they are not ions at all they're actually. The reason they're called covalent because they're sharing their valence electron covalent they're sharing their ions their valence electrons together they're not exchanging them as the ionic compounds.

Their melting points and boiling points are relatively low comparatively also because say for example sugar which we saw is only 186 degrees Celsius to melt. I'm sure you've melted sugar before you've melted it for Caramel and things like that, it's really easy to do inn your kitchen. As compared to salt which is almost, which is literally impossible to do. So the reason their melting point and boiling point is really based on their inner molecular forces. How highly they've actually bound together to each other and this is actually a whole another topic element itself which we can get into. So one last thing, solubility meaning how well they dissolve in water so both ionic compounds and covalent compounds pretty much can dissolve in water depending on what actual compounds they are but when you dissolve salt in water it breaks up into it's ions this is what we call electrolyte, they actually can create electricity.

Sugar molecules or covalent compounds when they're put in water they also dissolve as you probably know when you make tea or whatever they'll dissolve too but they don't break up, they just break up into their molecules they don't actually break up into their individual atoms as ionic compounds do. So this is the main difference really between ionic compounds and covalent compounds.