Learn about Advanced Placement Chemistry, Chemical bond 1, in this comprehensive video by bannanaiscool.
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We made ionic bonding sound kind of simple when we just say a cation loses electron to the anion and then the electrostatic force keeps them together to form a compound. Well actually there’s a series of steps and there’s always a series of steps that reactions go through to be able to get a net equation. None of the equation ever written really actually happen as that equation at any one time, it’s usually a series of equations that have to be added together to give a net equation. If we wanted to make lithium and fluorine come together as elements to form lithium fluoride, well that’s an easy equation to write and to balance. But here’s the thing, you’ve got to be able to understand that there’s a series of steps to go through like the lithium has to go from solid to gas first. So what do we call that? You need certain amount of energy to do that and that’s called the energy of sublimation because it’s going from solid to gas. What if lithium is in a gaseous state? We can now rip away its electron. That first ionization energy definition I gave you. And so, that equation is called the energy of ionization, ionization energy. Well alright, now we’ve got the electron removed from lithium. You see a series of steps, and the fluorine has to actually break a part of this F2. So that’s energy of dissociation that’s required there. And so we only need one so we divide one of those and we divide the equation by two. Then we give the electrons to that F gas to make F negative, and that’s electron affinity because the F has to bring it in. That’s going to release energy, so it’s going to have a negative delta H value. And then the lithium ion can combine with the fluoride ions to make lithium fluoride, but that is the largest releasing of energy. The positive coming together with the negative, but lots of positives and negatives coming together to form this big lattice network of Li’s and F’s together. So the lattice energy has the greatest delta H of all of these and it’s so exothermic, so negative that it makes this whole equation even though there were a lot of positive delta H’s here to begin with, very negative. And so, the lattice energy really shows that the reaction is going to favor releasing energy when bonds form. By the way, the lattice energy for a compound like MgO forming is actually four times as much as LiF because Li positive F negative, one and one—one times one for their charges equals one. But MgO, two positive two negative—two times two is four. You can just multiply the charges together to compare lattice energies. Delta H is from that equation, but the lattice energy here. That’s coulombs law by the way. Isn’t it fascinating that you can just look at the charges and compare energies? Very cool, but that’s chemistry.