# Use a line to represent the bond remember that the

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Use a line ( - ) to represent the bond. Remember that the line is actually two dots. Again using water as an example: H- O - H. The line between the H and O counts as two electrons for the H and two electrons for the O. Usually the central atom will be the single atom. Using H 2 O as the example, there is one O and two H's, so O is the central atom. Alert: If there are more than four atoms attached to the central atom, such as SF 6 , attach all six F atoms to the S. Notice there will be 12 electrons around S and it will violate the octet rule. This happens from occasionally.

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Step 3 Put 8 dots around the outer atoms ( all atoms except the central atom ) and remember that hydrogen can only have two dots. Again using water as an example: H- O - H. ( There are not 8 dots around the H because it only needs two, and the line represents 2 electrons. ) At this point, use one of the choices below. Step 4 Count the number of electrons used in the drawing: (A) Did not use enough electrons in the drawing: If not enough electrons were used, add the extra electrons to the central atom until the number of dots used in the drawing equals the number of valence electrons. To add dots to the central atom, you may attach them directly onto the central atom if there if room, or you may draw a dotted line extending from the central atom and put the two dots at the end of the dotted line. (B) Used too many dots in the drawing. If the correct number of valence electrons were used but the central atom does not have 8 electrons, use a lone pair on one of the outer atoms to form a double bond between that outer atom and the central atom. In other words, erase two dots off of one of the outer atoms and place a second line between the central atom and the outer atom with the erased electrons. Continue this process until the central atom has 8 electrons. This could result in several double bonds or a triple bond.
For a Molecule to be Polar: 1. Must contain at least two different elements. 2. The center of positive and negative must not coincide. ( If the Lewis Dot diagram has one lone pair or if it contains three different element, the molecule will be polar. It the Lewis Dot drawing contains no lone pairs and the same element at each position, it will be nonpolar.) Hybridization: Count the things around the central atom. ( Everything counts as one: single bond, double bond, triple bond, atoms, or loan pairs.) You must use one atomic orbital for each thing around the central atom. Your choice of atomic orbitals will always be one s orbital first, three p orbitals secondly, and five d orbitals last. Example: 4 things would need one s and three p= sp 3 . Five things would need one s, three p, and one d = sp 3 d.

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Answer Key Test 3 Chapters 6 and 7 (McMurry/Fay) 1. B 2. C ( HCN and CO 2 ) 3. D 4. C 5. Polar Covalent HCl ( two nonmetals, different electronegativity) 100% Covalent Cl 2 , H 2 (diatomic molecules) Ionic Compounds NaCl ( usually metal and nonmetal- electronegativity difference greater than 1.7) The difference in electronegativity determines the bond type.

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• Fall '08
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