MCAT Chemistry Ch. 3 Bonding & Chemical Interactions

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Octet Rule Exceptions
Incomplete Octet: elements that are stable with <8 electrons in valence shell. Hydrogen (stable w/ 2), helium (2), lithium (2), beryllium (4), & boron (6)
Octet Rule Exceptions
Expanded Octet: elements in period 3 or greater that can hold more than 8 valence electrons by placing them in the d orbitalPhosphorous (10), sulfur (12), chlorine (14), etc.
Octet Rule Exceptions
Odd Number of Electrons: molecules w/ odd # of valence electrons cannot distribute electrons so that each atom will have 8.Ex: nitric oxide has 11 valence electrons, uneven distribution
Ionic Bond
Electrons are not actually shared, but an electron is transferred from atom w/ low ionization energy to element w/ high electron affinity. This makes one of them a cation & the other an anion, & causes them to be electrostatically attracted to each other. Form into a crystal lattice shape, where opposing forces are minimized.Difference in electronegativity (ΔEN) >1.7
Ionic Compound Properties
Dissociate in water & polar solvents, have high melting points due to the great attraction between the cation & anion.
Covalent Bond
When two atoms share electrons to form a double, single, or triple bond. Can be polar or nonpolar
Bond Order
Refers to whether a bond is single, double, or triple. As bond order increases, bond strength increases, & bond length decreases.
Nonpolar bond
Both atoms have exact same electronegativity. Bonds are nonpolar if their ΔEN (difference in electronegativity) is < 0.5
Polar Bonds
Atoms have significant difference in electronegativity, ΔEN of 0.5 - 1.7, but not enough to transfer electrons & form an ionic bond.
Coordinate Covalent Bonds
Formed when single atom provides both bonding electrons & other atom doesn't give any. Most often found in Lewis acid-base chemistryFormed when single atom provides both bonding electrons & other atom doesn't give any. Most often found in Lewis acid-base chemistry
Formal Charge Formula
Formal Charge = V - Nnonbonding - 1/2(Nbonding) V = # of valence electrons the atom normally hasNnonbonding= # of valence electrons atom isn't using in bonds (lone pair electrons)Nbonding = # of valence electrons atom is using in bonds
Resonance Structure
Found in any molecule that has pi bonds, most stable are those w/ least amount of formal charges. Actual structure of molecule is a combination of all resonance structures.
Electronic Geometry (VSEPR Theory)
The position of all electrons in a molecule, whether bonding or nonbonding
Molecular Geometry (VSEPR Theory)
The position of only the bonding pairs of electrons in a molecule
Polarity of nonpolar molecules
Nonpolar molecules may contain nonpolar bonds, or polar bonds whose dipole moments cancel each other out (must look at molecular geometry of a molecule to check)