The electronegativity and so we take those four electrons, we divide them in half, so we give two electrons to one carbon and two electrons to the other carbon. Those electrons equally, because both of those carbons have the same value for So with four electrons, we're going to divide Have these four electrons, and now we're trying toĬompare the electronegativity of carbon, to carbon, and obviously, that's the same electronegativity. When we get to this double bond here between the two carbons, we Steal those electrons, and same thing over here, carbon's more electronegative, so carbon steals those electrons too. So we think aboutĮlectronegativity differences, and we know carbon is moreĮlectronegative than hydrogen, so carbon's going to So you put in our bonding electrons, and let's just pick one of the carbons to start off with, let's say we're talking about the carbon on the right. And let's verify that, let's put in our bonding electrons, and let's calculate the oxidation state of carbon by using our Should be minus four, because that total has to sum to zero, but this time we have two carbons, so minus four divided by two gives us minus two,Įach carbon should have an oxidation state of minus two. What's the oxidation state of carbon in this molecule? Well hydrogen should be plus one, and we have four of themįor a total of plus four. Let's move on to another molecule here, so C2H4, this is ethene, or ethylene. Let's count them up here, one, two, three, four, five, six, seven, eight, so four minus eight is equal to minus four, so we already knew that minus four was going So we can see thatĬarbon is now surrounded by eight electrons right, Carbon is more electronegative, so it takes those electrons, and all the way around. Carbon's going to hog thoseĮlectrons in this bond. More electronegative than hydrogen, so the two electrons in this bond here, carbon is going to take both of them, so So which is more electronegative? We know that carbon is The more electronegative atom is going to take all of the electrons in the bond, so we need to think about electronegativity differences, and we're comparing carbon to hydrogen. But now we need to thinkĪbout these covalent bonds as being ionic, and so We subtract the number of valence electrons in the bonded atom, or the number of valence electrons carbon has in our drawing. Next, we think about the oxidation state for carbon, and we start with a number of valence electrons in the free atom, or the number of valence electrons that carbon is supposed to have, and we know carbon is supposed to have four valence electrons, so from that number, So remember, when we're calculating the oxidation state using dot structures, we're thinking about bonding electrons, and we know that each bond consists of two electrons, so we need to put in the bonding electrons for all of our bonds. So let's go ahead and verify that with our dot structure. The sum has to be equal to zero, so we know that carbon's oxidation state must be minus four immediately, since we only have one carbon here. General chemistry approach where we know that hydrogen usually has an oxidation state of plus one, and we have four hydrogensįor a total of plus four. So let's start with methane, and let's find the oxidation state of carbon and methane. In earlier video, we've already seen the definition for oxidation state, and also how to calculate it. In this video, we're going to find the oxidation state of carbon in several different molecules. but if what you want is the most probable answer for most cases (say in school), you could rely on the factors i mentioned above (columns in periodic table, electronegativity, and octat rule) because the definition of "usual" itself is somehow arbitrary, and the situations one atom could be in a molecue varies so much (this video shows the examples for carbons clearly, and which is the most "usual" one? i'm not sure)ģ. actually there's no way to figure out "usual" oxidation state of an atom including that of oxygen as far as i knowĢ. thus by the formula, the oxidation state of oxygen in many cases = expected # of electrons - actual # of electrons = 6 - 8 = -2ġ. and it actually loves and steals them from whomever as much as possible (up to 8 in sum by octat rule)ģ. but in many cases, oxygen has stronger electronegativity (you can see this as a kind of the extend of loving and stealing electrons from others) than others bonded to it. oxygen has usually (or expectedly) 6 electrons around it by its place on the periodic table columns (say group-6)Ģ.
0 Comments
Leave a Reply. |