Cheatography
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Grade 12 chemistry course overview
This is a draft cheat sheet. It is a work in progress and is not finished yet.
Lewis Dot Diagrams: NASL Method
N - calculate needed as the sum of electrons needed for all atoms by the octet rule Exceptions (H=2, Be=4, B=6) |
A - calculate available as the sum of all valence electrons |
S - calculate shared as the difference between N and A. Divide S by 2 to obtain the number of bonds to be extended from the central atom |
L - calculate lone pair of electrons (dots) as the difference between A and S. |
Formal charge - Count the number of valence electrons the atom has in the molecule (both electrons in any un-bonded pairs and one electron for each bond). Subtract this number from the number of valence electrons from the periodic table |
Neutralize charges on neighboring atoms by moving unbonded electrons into bonds. Only if the (-) atom has an unbonded pair of electrons and the (+) atom is not completely filled. The exception is that if the (+) atom lies in a row further down on the periodic table than the (-) atom. In that case the charges can be transferred even if it means “overfilling” the atom. |
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Resonance, Bond Order, Bond Length, Bond Energy
Resonance |
Bond Order |
Bond Energy |
Bond Length |
Resonance structures have the same relative placement of atoms, but different locations of multiple bonds and lone electron pairs. |
The number of electron pairs being shared by any pair of bonded atoms |
The energy required to overcome this attraction |
Distance between two nuclei of two bonded atoms A higher bond order for a given pair of atoms will result in a shorter bond length, and higher bond energy |
Smaller formal charges (+ or -) are preferred over larger ones Like formal charges on adjacent atoms are not desirable. A more (-) formal charge should reside on a more electronegative atom in a molecule |
Single bond - bond order of 1 Double bond- bond order of 2 Triple bond - bond order of 3 |
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