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Unformatted text preview: rackets around all atoms and the charge in upper right corner. CHEM121 Exam 2 Study Guide Lewis structures for ternary oxyacids – A ternary oxyacid is a molecule that consists of H, O, and one other element. (Know that the formula for a ternary oxyacids starts with H.) – To draw the skeleton structure, write down the central atom, put the oxygens around it, then attach each hydrogen to a different oxygen. – Distribute valence electrons as usual. Lewis structures for hydrocarbons – hydrocarbon: consists of only C and H atoms – May contain several C atoms bonded to one another and surrounded by H atoms. Molecular Shapes and Polarity • Use the Lewis structure to determine the molecular shape and bond angle. • Use the Lewis structure to determine the general formula (A=central atom, X=# of outer atoms, E=# of lone pairs on central atom) and the steric number (SN=# of outer atoms + # of lone pairs on central atom). Know the following shapes and bond angles: ‐ AX2 and SN=2 → linear → 180° ∠ ‐ AX3 and SN=3→ trigonal planar → 120° ∠ ‐ AX4 and SN=4→ tetrahedral → 109.5° ∠ ‐ AX2E and SN=3→ bent or angular → <120° ∠ ‐ AX3E and SN=4→ trigonal pyramid → <109.5° ∠ ‐ AX2E2 and SN=4→ bent or angular → <109.5° ∠ • Use electronegativity to determine if a bond is polar or nonpolar covalent. • Be able to sketch a molecule after determining its shape and use dipole arrows to indicate the more electronegative atom in a polar covalent bond. • Use the 3D shape to determine if dipoles cancel or if there is an overall dipole to determine if a molecule is polar or nonpolar. page 2 of 4 Chapter 12: Liquids, Solids, and Intermolecular Forces Intermolecular Forces (IMF’s): attraction between 2 different molecules in a liquid or solid • Identify the type(s) of intermolecular force for a molecule as London/dispersion forces, dipole‐
dipole forces, hydrogen bonding, or ion‐diple forces. – Recognize that polar molecules experience London/dispersion forces a...
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