Unit 8: Bonding and Molecular Geometry

Bonding - a chemical bond forms when the potential energy of the bonded atoms is less than the potential energy of the separate atoms

Lewis structures - that allow us to predict many properties of molecules (Electron Dot Structure)

Isoelectronic group of ions - ions that have the same number and configuration of electrons

Ionic Bonds - bond formed by electrostatic attraction between (+) and (-) ion

Covalent Bonds - Bond that share valence electrons, share sufficient number of electrons in order to achieve a noble gas electron configuration

Octet rule - tendency to have 8ei in outer shells (It’s 2e- for H2)

Coordinate Covalent bond - bonds between atoms where both electrons are donated by one of the atoms

Double bond - two pairs of electrons are shared between atoms

Triple Bonds - three pairs of electrons are shared between atoms

Polar covalent bond - the bonding electrons spend more time near one of the two atoms

Nonpolar covalent bond - for alike atoms (as in H2) the bonding electrons are shared equally

Polar bond - shared not equally (HCl)

Electronegativity - ability of an atom to draw bonding electrons to itself, increases from lower-left to upper-right corner

Polarity of Bond - the absolute difference in electronegativity of two bonded atoms

Nonpolar Bond - when the difference in electronegativity is small <0.5

Polar Bond - when the difference in electronegativity is larger >0.5

Ionic Bond - when the difference in electronegativity exceeds about 1.8

Steps to drawing Lewis Structures - 1. find total of all valence e- 2. arrange atoms radially with the least electronegative in the center placing one pair of e- per bond 3. distribute remaining electrons to electronegative atoms to satisfy octet rule 4. distribute any remaining electrons to center atom

Delocalized Bonding: Resonance - can represented by two different Lewis e-dot formulas or pair is shared (O3)

Expanded Octet Exception - the central atom has more tha n8 electrons (3rd period or greater)

Fewer then 8 Electrons Exception - the central atom does not need a full octet (very small atoms smaller than C)

Formal Charge - used to determine which structure is the most likely

Bond Theory VSEPR Model - Predicts shapes of molecules by assuming that the valence e pairs are arranged as far from one another as possible (to minimize repulsion)

electron pair arrangement steps - 1. Draw Lewis structure 2. Determine how many electron pairs are around the central atom 3. Arrange electron pairs according to VSEPR 4. Obtain geometry from directions of bonding pairs

Arrangement of 2 electron pairs - linear (180 degrees)

Arrangement of 3 electron pairs - trigonal planar (120 degrees)

Arrangement of 4 electron pairs - tetrahedral (109.5 degrees)

Arrangement of 5 electron pairs - trigonal bipyramidal (90, 120 degrees)

Arrangement of 6 electron pairs - octahedral (90 degrees)

Molecular Geometry of an atom with 2 bonding pairs and 0 lone pairs - linear

Molecular Geometry of an atom with 3 bonding pairs and 0 lone pairs - trigonal planar

Molecular Geometry of an atom with 2 bonding pairs and 1 lone pair - bent or angular

Molecular Geometry of an atom with 4 bonding pairs and 0 lone pairs - tetrahedral

Molecular Geometry of an atom with 3 bonding pairs and 1 lone pair - trigonal pyramidal

Molecular Geometry of an atom with 2 bonding pairs and 2 lone pairs - bent or angular

Molecular Geometry of an atom with 5 bonding pairs and 0 lone pairs -Trigonal bipyramindal

Molecular Geometry of an atom with 4 bonding pairs and 1 lone pairs - Seesaw

Molecular Geometry of an atom with 3 bonding pairs and 2 lone pairs - T-Shaped

Molecular Geometry of an atom with 2 bonding pairs and 3 lone pairs - linear

Molecular Geometry of an atom with 6 bonding pairs and 0 lone pairs - Octahedral

Molecular Geometry of an atom with 5 bonding pairs and 1 lone pairs - Square Pyramidal

Molecular Geometry of an atom with 4 bonding pairs and 2 lone pairs - Square Planar

Dipole Moment - a measure of the degree of charge separation in a molecule

Nonpolar Molecule (Dipole) - perfectly symmetric, having a 0 dipole moment

Polar Molecule (Dipole) - exhibiting any asymmetry, having a nonzero dipole moment