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KotzVSEPROutline - Covalent Bonding Outline...

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Covalent Bonding Outline KotzVSEPRoutline.doc Covalent bonding is the sharing of two or more electrons between atoms of similar electron attraction. Covalent bonding occurs primarily between nonmetals Covalent Bonding -Generally between nonmetals -Electrons are shared to achieve a stable octet. -Usually takes place between valence electrons (outermost s and p sublevel electrons) -Lewis Dot Structures - Provide a method of visualizing the valence electrons for an atom. Writing Lewis Dot Structures for isolated atoms Electron Placement Order Writing Lewis Structures for Molecules 1. Determine the most likely arrangement of atoms. a. Least EN atom is usually in the center. b. Molecules are often symmetrical. c. Hydrogen is never a central atom and can only have a “duet”. 2. Determine the total number of valence electrons the molecule possesses. 3. Fill in the "octets" of the outer atoms (Place electrons in pairs around the outer atoms) 4. Check for an octet on the central atom. a. If the central atom has an octet and there are no leftover electrons, then you are done. b. If the central atom doesn't contain an octet, consider a double or triple bond (two or three pairs of electrons shared between atoms) c. If there are electrons left over, place them as lone pairs on the central atom. Notes: -Sometimes a line is used between atoms to represent a pair of electrons. -The Lewis Dot Structure doesn't tell you anything about the geometry of the molecule. Electronegativity is a value assigned to atoms that gives a sense of the relative tendency for an atom to draw electrons towards it. These values were developed by Linus Pauling. The most electronegative elements are the nonmetals in the upper-right corner of the periodic table (F, O, N, Cl) and the least electronegative are the metals in the lower-left corner (Cs, Fr, etc.). A high positive value indicates a high attraction for electrons in a bond and a low (or fractional) number indicates a relatively low attraction. X 1 2 4 3 7 5 6 8 Imaginary box Element Symbol Electron dot arrangement
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Fluorine at 4.0 has the highest electronegativity and cesium/francium at 0.7 have the lowest. The noble gases are not assigned electronegativity values for reasons which will become apparent. The question arises, what would make an atom attracted to an electron and why does it primarily happen to nonmetals ? The answer lies in the configuration of the electrons around the atom and the energy associated with that arrangement. Recall that the quantum model of the atom has electrons filling energy levels (the n number) and sublevels (the l number). The valence electrons are the s and p electrons in the outermost energy level of that atom. These are the ones that primarily take part in the bonding process. If you notice, all noble gases have filled s and p sublevels (except He which only has an s sublevel). With 2 electrons in the s sublevel and 6 electrons in the p orbitals, there are a total of 8 electrons which chemists refer to as an octet .
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KotzVSEPROutline - Covalent Bonding Outline...

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