Review Quiz 5
Chapter 8, (8.1-8.12)
Electronegativity (# 13, 15, 21, 23, 25, 29)
-ability of an atom in a molecule to attract electrons to itself.
A covalent bond is the sharing of electron pairs between two atoms.
pure covalent bond= equal sharing of shared electron pairs
polar covalent bond = unequal sharing of electrons
An ionic bond is a transfer of electrons from one atom to another to form
ions.
-Anions are larger than neutral atom.
-Cations are smaller than neutral atom.
Isoelectronic atoms: (# 33, 35, 37)
-same number of electrons
-different number of protons
If # electrons constant, only look at #p to predict trends in size
Ions with most protons has stronger pull on the same # electrons
Lattice energy: (#43)
-change in energy when separated gaseous ions are packed together to form
a solid.
-follows Coulomb’s law E (Q1Q2)/r
-ions with larger charges are favored
Enthalpy for a reaction: (# 53, 57, 61)
∆H = ∆H bonds broken - ∆H bonds formed
- ∆ H = exothermic rxn
+ ∆ H = endothermic rxn
Lewis Structures: (# 67, 69, 71, 73)
Nonmetals form covalent bonds
-room for 8 valence electrons (octet rule)
- Hydrogen (duet rule) 1s orbital
Atom listed first is central atom (if different you should get hints)
Be and B are examples for molecules that have fewer than 8 electrons.
(BeH2 and BH3)
Row 3 and heavier nonmetals can have more than 8 electrons, but only if
they have to.
Satisfy the octet rule first; exceptions occur when there are no other options.
(PF5, SCl6, IF5…)
Generally, molecules do not like unpaired electrons. Odd electron molecules
are very reactive.
Formal Charge: (# 81, 83)
Assigned electrons = lone pair electrons + ½ (bonded electrons)
F. C. = # Valence electrons on free atom - Assigned electrons
Best structure is: F. C. = zero or
F. C. is negative on most electronegative atom
Isomers:
Same formula, different properties
Same type and number of atoms - ARRANGEMENT different.
Can I build the structure differently? Think tinker toys
Resonance:
-occurs when more than one valid Lewis structure can be drawn for a
molecule.
- only differs in positions of electron pairs: atoms remain connected in the
same way
- COMMON characteristics are a multiple bond (double bond, triple bond)
that moves from one position to another.
- The actual structure exists as an average of all the resonance structures.
Molecular Geometry:
Electrons repel each other, so a molecule adopts a geometry to place electron
pairs around a central atom as far apart as possible.
# Bonded atoms plus
Lone pairs @ central atom
Geometry
Bond
Angle
2
linear
180˚
3
trigonal planar
120˚
4
tetrahedral
109.5˚
5
trigonal
bipyramidal
90˚, 120˚
octahedral
90˚
6
Polar molecules:
1. polar bonds
2. a structure that does not allow the bond dipoles to cancel each
other.