初三英语作文,90秒rules in the chemistry（what we can do,and what we

初三英语作文,90秒
rules in the chemistry（what we can do,and what we can't do）

The Golden Rules of Organic Chemistry
Your goal should be to understand,not memorize organic chemistry.The following 7 Golden Rules should be learned at the beginning of this semester.These simple ideas explain a very large number of things about the way organic molecules interact.Thus,understanding the 7 Golden Rules will allow you to develop an intuitive feel for organic chemistry,and things will make sense!(Warning:this means you will start thinking like a chemist,but,of course,no one needs to know if you don't want them to know.)
1.Atoms prefer filled valence shells.This rule explains why atoms make bonds,and the type of bonds created.A corollary is that centers of electron density (bonds and lone pairs of electrons) repel each other so they stay as far apart as possible.This latter rule,the basis for the so-called VSEPR model,explains 3-dimensional molecular structure.
2.The most important question in chemistry is "Where are the electrons?" The answer is that electrons are generally in higher amounts around the more electronegative atoms (e.g.F,Cl,O,N).The electronegative atoms pull electron density away from the less electronegative atoms (e.g.C,H) to which they are bonded.Thus,understanding electronegativities provides a simple method of deciding which portions of a molecule have a relatively high electron density,and which portions have a relatively low electron density.
3.Nature hates unpaired electrons.If a molecule must have an unpaired electron (a.k.a.radical),it is better to have the unpaired electron distributed over as many atoms as possible through resonance,inductive effects,and hyperconjugation.
4.Nature hates localized charges.If a molecule must have a charge,it is better to have the charge distributed over as many atoms as possible through resonance,inductive effects,and hyperconjugation.In addition,when given the choice,it is better to have more negative charge on a more electronegative atom (e.g.O),and more positive charge on a less electronegative atom (e.g.C).
5.Most reactions involve nucleophiles (molecules with a location of particularly high electron density) attacking electrophiles (molecules with a location of particularly low electron density).When in doubt,transfer a proton!Thus,simply understanding where electrons are provides you with the best way of analyzing new molecules so that you will be able to PREDICT how they will react.
6.Steric interactions (atoms bumping into each other) can prevent reactions by keeping the reactive atoms away from each other.
7.Pi electrons prefer to be delocalized over as many adjacent sp2 hybridized atoms (or sp hybridized atoms in some cases) as possible,and aromaticity is the most stable form of pi electron delocalization.Pi electrons cannot delocalize onto or through sp3 hybridized atoms since an sp3 atom has no 2p orbital available.