:) m. --- marc garrett <[EMAIL PROTECTED]> wrote: > A DIALOGUE WITH SARAH, AGED 3: IN WHICH IT IS SHOWN > THAT IF YOUR DAD IS > A CHEMISTRY PROFESSOR, ASKING WHY CAN BE > DANGEROUS. > > http://www.scribd.com/word/html_iframe/1063?guid=27zta2fh7pppm > > By Stephen McNeil > > - FROM THE ARCHIVES - > > SARAH: Daddy, were you in the shower? > > DAD: Yes, I was in the shower. > > SARAH: Why? > > DAD: I was dirty. The shower gets me clean. > > SARAH: Why? > > DAD: Why does the shower get me clean? > > SARAH: Yes. > > DAD: Because the water washes the dirt away when I > use soap. > > SARAH: Why? > > DAD: Why do I use soap? > > SARAH: Yes. > > DAD: Because the soap grabs the dirt and lets the > water wash it off. > > SARAH: Why? > > DAD: Why does the soap grab the dirt? > > SARAH: Yes. > > DAD: Because soap is a surfactant. > > SARAH: Why? > > DAD: Why is soap a surfactant? > > SARAH: Yes. > > DAD: That is an EXCELLENT question. Soap is a > surfactant because it > forms water-soluble micelles that trap the otherwise > insoluble dirt and > oil particles. > > SARAH: Why? > > DAD: Why does soap form micelles? > > SARAH: Yes. > > DAD: Soap molecules are long chains with a polar, > hydrophilic head and a > non-polar, hydrophobic tail. Can you say > hydrophilic? > > SARAH: Aidrofawwic > > DAD: And can you say hydrophobic? > > SARAH: Aidrofawwic > > DAD: Excellent! The word hydrophobic means that it > avoids water. > > SARAH: Why? > > DAD: Why does it mean that? > > SARAH: Yes. > > DAD: Its Greek! Hydro means water and phobic > means fear of. > Phobos is fear. So hydrophobic means afraid of > water. > > SARAH: Like a monster? > > DAD: You mean, like being afraid of a monster? > > SARAH: Yes. > > DAD: A scary monster, sure. If you were afraid of a > monster, a Greek > person would say you were gorgophobic. > > (pause) > > SARAH: (rolls her eyes) I thought we were talking > about soap. > > DAD: We are talking about soap. > > (longish pause) > > SARAH: Why? > > DAD: Why do the molecules have a hydrophilic head > and a hydrophobic tail? > > SARAH: Yes. > > DAD: Because the C-O bonds in the head are highly > polar, and the C-H > bonds in the tail are effectively non-polar. > > SARAH: Why? > > DAD: Because while carbon and hydrogen have almost > the same > electronegativity, oxygen is far more > electronegative, thereby > polarizing the C-O bonds. > > SARAH: Why? > > DAD: Why is oxygen more electronegative than carbon > and hydrogen? > > SARAH: Yes. > > DAD: Thats complicated. There are different answers > to that question, > depending on whether youre talking about the > Pauling or Mulliken > electronegativity scales. The Pauling scale is based > on homo- versus > heteronuclear bond strength differences, while the > Mulliken scale is > based on the atomic properties of electron affinity > and ionization > energy. But it really all comes down to effective > nuclear charge. The > valence electrons in an oxygen atom have a lower > energy than those of a > carbon atom, and electrons shared between them are > held more tightly to > the oxygen, because electrons in an oxygen atom > experience a greater > nuclear charge and therefore a stronger attraction > to the atomic > nucleus! Cool, huh? > > (pause) > > SARAH: I dont get it. > > DAD: Thats OK. Neither do most of my students. > > > > _______________________________________________ > NetBehaviour mailing list > [email protected] > http://www.netbehaviour.org/mailman/listinfo/netbehaviour >
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