CHEM 154 UNITS 2- 11 EXAM QUESTIONS WITH CORRECT ANSWERS WITH A 100 % GUARANTEED PASS
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Course
CHEM 154
Institution
CHEM 154
QUANTUM MECHANICS - The theory explaining why energies and angular momenta of atoms and molecules are quantized
VALENCE ELECTRON (SPECIAL FACT) - Valence electrons are involved in the formation of bonds and core electrons are not involved in chemical bonding.
ATOMIC RADIUS - - Calculated by m...
COULOMBS LAW - ✔✔- Core electrons are close to the nucleus and effectively screen some of its
positive charge from valence electrons further away.
,- Valence electron "feels" an effective nuclear charge (ZEFF) that is less than the actual nuclear charge Z.
IONIZATION ENERGY (IE) - ✔✔FOR ATOMS/MOLECULES/IONS:
- Minimum energy required to remove a single electron from an atom/molecule/ion in its gaseous state.
FOR SOLIDS:
-Minimum energy required to remove an electron from the valence band of the solid.
ELECTRON AFFINITY (EA) - ✔✔FOR MOLECULES/ATOMS:
- Energy change resulting from the addition of an electron to an atom/molecule in the gaseous state.
FOR SOLIDS:
- Minimum energy change resulting from adding an electron to the lowest lying electronic states (of the
conduction band) of the solid.
ELECTRONEGATIVITY (EN/X) - ✔✔- Ability of an atom to attract shared electrons to itself in the form of a
chemical bond
- Greater EN = greatter affinity for electrons.
- Refers to atoms in a bond, therefore NOT an atomic property.
- Calculated NOT measured value.
- the GREATER the EN, the MORE polarized a chemical bond.
WHY DO BONDS FORM - ✔✔- Bond length is the distance at which the atoms have the lowest PE.
- At low distances, electrostatic repulsions cause PE to increase rapidly.
- As distance decreases, attractive interactions decrease PE.
BOND ENERGIES/BOND ORDER - ✔✔- Exothermic process when bonds are formed.
- Bond energy required to break a covalent bond, bond order is number of electron pairs shared by two
atoms in a covalent bond.
, LATTICE ENERGY - ✔✔Energy required to disassociate an ionic solid into its separate ions, increases with
charges on the ions or as the distance between charges decreases.
POLAR COVALENT BONDS - ✔✔In covalent bonds electrons are not shared equally (electron density) due
to the differences in electronegativity.
INCOMPLETE/EXCEPTIONS OCTET - ✔✔- Elements in group 13 follow a "sextet" rule (three electron
groups surrounding them)
- Ex. Boron
-Molecules with odd number of electrons have unpaired electrons, this is called radicals.
-Ex. NO
- Elements on Period 3 can expand their octets.
- Ex. PCl3 expands to PCl5
RESONANCE STRUCTURES - ✔✔- Same arrangement of atoms produce more than one lewis structure.
- Indicates delocalized bond is present.
- Contributes to the actual molecular structure (Resonance Hybrid, NOT A LEWIS STRUCTURE).
- If there are multiple hypervalent resonance structures, ONLY positive/zero formal charges on the
central atom are VALID
VALENCE SHELL ELECTRON PAIR REPULSION (VSEPR) - ✔✔- Theory that predicts molecular shape by
treating atoms in a molecule as point charges that are favoured to be as far away from each other as
possible.
- Reason why atoms want to stay away from each other is covalent bonds and lone pairs have repulsions
-Therefore NUMBER OF LONE PAIRS AND NUMBER OF TERMINAL ATOMS/BOND PAIRS CONNECTED TO
THE CENTRAL ATOM DETERMINE THE MOLECULAR SHAPE
PARENT SHAPES - ✔✔Total number of lone pairs and terminal atoms/bond pairs are the same for
different molecules
TRIGONAL PLANAR PARENT SHAPE - ✔✔TRIGONAL PLANAR
LP: 0 BP: 3 ANGLE: 120
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