October 2nd
Detour into discussion of the level of this class: should it be challenging to people who had advanced chemistry in high school, or accessible to folks who have never had a chemistry class before this one?
Reactivity
Excluding the far-right column of the periodic table (the "noble" or "inert" gases), reactivity increases as you head toward the upper-right and lower-left corners.
First, recall the periodic table with the numbers of outer-shell electrons:
Reactivity
Excluding the far-right column of the periodic table (the "noble" or "inert" gases), reactivity increases as you head toward the upper-right and lower-left corners.
First, recall the periodic table with the numbers of outer-shell electrons:
Recall also that atoms are most stable when they have a full outer shell, and that there are two ways to get to full: get enough electrons to fill the current outer shell, or get rid of all the electrons in the current outer shell so the atom ends up at the full shell just inside the current outer shell. So, an atom can gain enough electrons to get up to eight, or get rid of enough to get down to zero.
(continued below next table)
(continued below next table)
As far as whether the atom gains or loses electrons, it will do whichever involves the fewest electrons. Look in the table above for fluorine. (Atomic number 9, symbol "F".) It has seven electrons in its outer shell, so to get to a full shell it can either gain one electron or lose seven. It will go the easy way: gain one electron. To the left of fluorine is oxygen, which has six electrons in its outer shell: it can gain two or lose six, so it gains two. Same row, far left, is lithium. Lithium has one electron in its outer shell, so it can lose that one or gain seven: it loses one because that is the easier way to go.
For reactivity, elements that transfer (lose OR gain) just one electron are more reactive than those that transfer two: it is a whole lot easier to gain or get rid of one electron than it is to do one electron and then have to do another one.
Look at the halogens (F, Cl, Br, I). They all want to gain one electron. The positive charge in the nucleus is what pulls in and hold electrons. Fluorine's shell is closer to the nucleus than is the outer shell for chlorine, and chlorine's is closer than is the outer shell for bromine, etc. The further away from the nucleus you get, the less pull the nucleus exerts, and so the harder it is for the atom to pull an electron in from, say, another atom. Therefore, fluorine is more reactive than is chlorine, and chlorine is more reactive than bromine, etc.
The reason goes the other way in the far left column of the table. There, all the elements - Li, Na, K, Rb, Cs - want to get rid of one electron. As with the halogens, the further down the column you go, the further the outermost shell is from the nucleus. However, since these all want to get rid of the one electron in the outer shell, now the one furthest down the column is the most reactive: it is much easier to get that electron away from cesium than it is from lithium.
For reactivity, elements that transfer (lose OR gain) just one electron are more reactive than those that transfer two: it is a whole lot easier to gain or get rid of one electron than it is to do one electron and then have to do another one.
Look at the halogens (F, Cl, Br, I). They all want to gain one electron. The positive charge in the nucleus is what pulls in and hold electrons. Fluorine's shell is closer to the nucleus than is the outer shell for chlorine, and chlorine's is closer than is the outer shell for bromine, etc. The further away from the nucleus you get, the less pull the nucleus exerts, and so the harder it is for the atom to pull an electron in from, say, another atom. Therefore, fluorine is more reactive than is chlorine, and chlorine is more reactive than bromine, etc.
The reason goes the other way in the far left column of the table. There, all the elements - Li, Na, K, Rb, Cs - want to get rid of one electron. As with the halogens, the further down the column you go, the further the outermost shell is from the nucleus. However, since these all want to get rid of the one electron in the outer shell, now the one furthest down the column is the most reactive: it is much easier to get that electron away from cesium than it is from lithium.
Ionic compounds
The review of ionic compounds in the lecture notes of October 4 covers the major points.
The review of ionic compounds in the lecture notes of October 4 covers the major points.