Ch. 3: Bonding and Chemical Interactions Flashcards
Chemical bonds can be…
Ionic or covalent
Elements form bonds to…
Attain a noble gas like electron configuration
Octet Rule
States that elements will be most stable with 8 valence electrons. However, there are many exceptions to this rule:
- Elements w an incomplete octet are stable with fewer than 8 electrons and include H, He, Li, Be, and B
- Elements with an expanded octet are stable w more than 8 electrons and include all elements in period 3 or greater
- Compounds with an odd number of electrons cannot have 8 electrons on each element
Ionic Bonds
Formed via the transfer of one or more electrons from an element with a relatively low ionization energy to an element w a relatively high electron affinity (🔺EN > 1.7). Usually between metals and nonmetals. Form Crystalline lattices– large, organized arrays of ions
Ionic Compounds
Unique physical and chemical properties
- Tend to dissociate in water and other polar solvents
- Tend to have high melting points
Covalent Bond
Formed via the sharing of electrons between 2 elements of similar electronegativities
Bond Order
Refers to whether a covalent bond is a single bond, double bond, or triple bond. As bond order increases, bond strength increases, bond energy increases and bond length decreases
Covalent Bond Characterization by Polarity
Nonpolar bonds: result in molecules in which both atoms have exactly the same electronegativity; some bonds are considered nonpolar when there is a very samll diff in electronegativity between the atoms (🔺EN < 0.5), even though they are technically slightly polar
Polar Bonds: Form when there is a significant diff in electronegativities (EN = 0.5 to 1.7), but not enough to transfer electrons and form an ionic bond. In a polar bond, the more electronegative element takes on a partial negative charge, and the less electronegative element takes on a partial positive charge
Coordinate Covalent Bonds
Result when a single atom provides both bonding electrons while the other atom does not contribute any; coordinate covalent bonds are most often found in Lewis acid-base chemistry
Lewis Dot Symbols
Chemical representation of an atom’s valence electrons
Formal charges
Exist when an atom is surrounded by more or fewer valence electrons than it has in its neutral state (assuming equal sharing of electrons in a bond)
Resonance Structures
For any molecule with a pi system of electrons, resonance structures exist; these represent all of the possible configurations of electrons- stable and unstable- that contribute to the overall structure
Valence Shell Electron Pair Repulsion (VSEPR) theory
Predicts the 3D molecular geometry of covalently bonded molecules. In this theory, electrons-whether bonding or nonbonding-arrange themselves to be as far apart as possible from each other in 3D space, leading to characteristic geometries
Nonbonding electrons…
Exert more repulsion than bonding electrons bc they reside closer to the nucleus
Electronic Geometry
Refers to the position of all electrons in a molecule whether bonding or nonbonding
Molecular Geometry
Refers to the position of only the bonding pairs of electrons in a molecule
Polarity of Molecules
Dependent on the dipole moment of each bond and the sum of the dipole moment of each bond and the sume of the dipole moments in a molecular structure
- All polar molecules contain polar bonds
- Nonpolar molecules may contain nonpolar bonds, or polar bonds w dipole moments that cancel each other
Sigma Bonds
Result of head to head overlap
Pi Bonds
Result of the overlap of 2 parallel electron cloud densities
Intermolecular Forces
Electrostatic attractions between molecules. They are significantly weaker than covalent bonds (which are weaker than ionic bonds)
London Dispersion Forces
Weakest interactions, but are present in all atoms and molecules. As the size of the atom or structure increases, so does the corresponding London dispersion force
Dipole-Dipole Interactions
Occur between the oppositely charged ends of polar molecules, are stronger than London forces; these interactions are evident in the solid and liquid phases, but negligible in the gas phase due to the distance between particles
Hydrogen Bonds
Are a specialized subset of dipole-dipole interactions involved in intra- and intermlecular attraction; hydrogen bonding occcurs when hydrogen is bonded to one of 3 very electronegative- atoms (flourine, oxygen, or nitrogen)
