Energywise one gram of hydrogen 20 tons of coal Chapter 4 Chemical bonds Will

Energywise one gram of hydrogen 20 tons of coal

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“Energywise”: one gram of hydrogen = 20 tons of coal
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Chapter 4: Chemical bonds Will look at: Bonds between atoms of same and different types Bonding patterns can be used to differentiate between three forms of elemental carbon Ionic vs. covalent Polarity of bonds Properties of molecules, including reactivity Shapes of molecules Stable Electron Configurations Fact: Noble gases, are inert (do not react) Theory: each has an octet of electrons in its outermost shell (max. # of electrons) Deduction: other elements that can alter their electron structures to become like those of noble gases would become less reactive by doing so Sodium can lose a valence electron to form an octet structure o Na + (sodium ion) and Ne are isoelectronic (have the same number of electrons) Chlorine can gain an electron, electron structure becomes like argon Lewis (Electron Dot) symbols G.N. Lewis (1875 – 1946) o Developed a method of visually representing the valence electrons as dots around the symbol of an atom Sodium reacts with chlorine (theory) Sodium reacts very well with chlorine Simple electron transfer reaction This is a very important reaction type in biology, e.g. photosynthesis Na + ions and Cl - have opposite charges and attract each other; called an electrostatic attraction The resulting attraction is an ionic bond Ionic compounds are held together by ionic bonds and exist in a crystal o Sodium chloride = “extended solid”
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Rules for Sketching Lewis Structures. E.g. CHOF 1. Count valence electrons C H O F 4 1 6 7 = 18 valence electrons 2. Sketch a skeletal structure *When in doubt, place least electronegative non-hydrogen atom, which is carbon in this example, at the center 2. Place electrons as pairs around outer atoms to fulfill the octet rule 3. Subtract the electrons used so far from the total number of valence electrons. Place any remaining electrons around the central atom 4. If the central atom lacks an octet, move one or more lone pairs from an outer atom to a double or triple bond to complete an octet Odd electron molecules: Free radicals An atom or molecule with an unpaired electron is known as a free radical. These are generally quite reactive Examples include: (note that all are uncharged) o NO, NO 2 , OH, Cl Molecular shapes: The VSEPR Theory o Properties of biomolecules, including DNA, depend on their shapes o Valence Shell Electron Pair Repulsion o Predicts the shape of molecules and polyatomic ions based on repulsion of electron pairs on central atoms Molecular shapes o Linear o Bent o Triangular trigonal planar o Pyramidal trigonal pyramidal o Tetrahedral
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