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Organic chem chemical bonding and molecular geometry mindmap/study notes
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- University Of South Africa (Unisa)
Chemical bonding and molecular geometry for organic chem. In detail, colour coded and summarized
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The hypothetical charge the atom would have if we could redistribute theelectrons in the bonds evenly between the atoms
Equal to the number of valence electrons (Nve), minus the number of lone pair Lewis dot notation: a way of describing the outer shell
electrons (Nlp) and minus half the number of the bonding electrons (Nbe). (valence shell) of an atom’s electrons.
Formal charge = Nve – (Nlp + ½ Nbe) Dots are drawn around the symbol of the element to
Tells us the accuracy and stability of the Lewis structure represent the electrons in the valence shell of the atom
Lewis structures with the lowest magnitude of formal charges are more stable. Lewis structures: molecular representations that show the
The more electronegative atoms should have negative formal charges. connectivity/bonding of the atoms and any formal charge
Adjacent atoms should have opposite formal charges. Indicate bond polarity with partial negative (δ-) and partia
Molecular structure: The arrangement of atoms in a molecule or ion positive (δ+) charges.
A molecular structure in which all formal charges are zero is preferable to one Attach a positive charge to the respective atoms in a catio
in which some formal charges are not zero. Attach a negative charge to the respective atoms in an an
If the Lewis structure must have nonzero formal charges, the arrangement with Formal charges are indicated on the respective atoms in a
the smallest nonzero formal charges is preferable. molecule or compound
The octet rule: The tendency of main group atoms to form
enough bonds to obtain eight valence electrons
Formal charges - Exceptions:
1. Odd-electron molecules have an odd number of valence
Refers to a way of describing the structure of a molecule that electrons, therefore have an unpaired electron.
can't be represented by just one simple diagram. 2. Electron-deficient molecules have a central atom that ha
The molecule has several possible structures (resonance fewer electrons than needed for a noble gas configuration
structures) that differ only in the arrangement of electrons, 3. Hypervalent molecules have a central atom that has more
particularly in double bonds or lone pairs. electrons than needed for a noble gas configuration.
The real structure of the molecule is a hybrid of all these
resonance structures (resonance hybrid), meaning the electrons
Resonance Lewis symbols and structures
are spread out/delocalized over several atoms.This helps
stabilize the molecule
Resonance structures are enclosed in square brackets
A double-headed arrow between Lewis structures indicates that CHEMICAL BONDING AND MOLECULAR
they are resonance forms. GEOMETRY
Negative charges prefer to be on the more electronegative atom
Positive charges on the more electropositive atoms
Bond energy and length
Bond energy: the amount of energy required to break a bond in kj.mol Molecular polarity
Bond strength: how strongly each atom is joined to another atom,
Bond length: the distance between the nuclei of two bonded atoms. Dipole Moments: The measureme
Triple bonds are the shortest and strongest, while single bonds are the polarity of a molecule, depend
the longest and weakest. the magnitude of the charge sepa
Enthalpy change: ΔH=ƩD bonds broken - ƩD bonds formed and distance between charges.
Lattice energy: the energy required to separate 1 mole of the solid The magnitude of a bond dipole m
into its component gaseous ions is mu (µ)
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