Ch 3 - Bonding Flashcards
Which (6) elements almost always follow the octet rule?
C carbon N nitrogen O oxygen F fluorine S sulfur M magnesium
What is ionic bonding?
Atom w low electron affinity and atom with high affinity bond.
Electrostatic attraction is what forms the bond and keeps the atoms close to each other
Crystalline Lattice structures: rows of cations and anions, not individual molecular bonds
Usually want a difference in electronegativity above 1.7
What is a covalent bond?
A bond where a pair of electrons is shared, usually between non-metals that have similar ELECTRONEGATIVITY values
Polar or nonpolar bond?
Nonpolar - when the electrons are shared equally (small or no diff in electronegativity between atoms)
Polar - shared unequally (about 0.5 to 1.7 diff in electronegativity, significant but not enough to transfer electrons to form an ionic bond)
What is a coordinate covalent bond?
When BOTH the shared electrons come from one element/atom
Most often found in Lewis acid-base chemistry
What are the exceptions to the octet rule?
Hydrogen (can only have 2 valence electrons)
Lithium and beryllium (2 and 4 valence electrons respectively)
Boron (six valence electrons)
Elements in period 2 and greater (can expand the valence shell to include more than 8 electrons by incorporating d-orbitals)
Characteristics of ionic compounds:
How do they behave?
- Tend to dissociate in water and other polar solvents
2. Ionic solids tend to have HIGH melting points
What is Bond order?
Refers to whether the covalent bond is single, double, or triple
As BOND ORDER increase, bond strength and energy increase, and bond length decreases
When is there is formal charge to an atom in a covalent bond?
When the atom has more or less electrons than it normally would in the valence shell, in neutral state (assuming equal sharing of electrons)
What is the formulae for FORMAL CHARGE?
V - N.nonbond - 1/2 N.bond
V= normal # of valence electrons N.nonbond = number of unbounded electrons N.bond= number of bonding electrons
** calculated for each atom seperately
What are resonance structures?
When do they exist?
Represent all the possible configurations of electrons (stable and unstable) that contribute to the overall structure
Delocalizes electrons and charges over a ‘pi’ system.
They exist for any molecule with a ip system of electrons
Why is resonance important in chemistry (ie organic chemistry)?
Allows greater stability
What is the VSEPR theory?
Valence shell electron pair repulsion
Predicts the 3-D molecular geometry of molecules with covalent bonds
Nonbond electrons exert more repulsion than bonded e’s
MOLECULAR GEOMETRY versus ELECTRONIC GEOMETRY
Molecular: refers only to bonded electrons in a molecule
Electronic: refers to the position of all electrons in a molecule, both bonded and nonbonded
Molecular geometries as per VSEPR theory:
6
2 - linear 3- regional planar (also linear) 4- trrahedral 5- regional bipiramidal 6- octahedral
