Unit 4: Chemical Bonding and Molecular Structure Chapter 6 Notes ...

2. can not be broken up by dissolving in water or melting, so never conduct
electricity (exception later in the year)
3. bond length and bond energy vary depending on the types of atoms bonded
D. Intermolecular forces (force of attraction between molecules)
1. much weaker than forces between ionic formula units
2. compared to ionic compounds:
a. lower melting points and boiling points
b. do not conduct electricity
III. The Octet Rule
A. Chemical compounds tend to form so that each atom, by gaining, losing, or sharing
electrons, has an octet of electrons in its highest occupied energy level.
B. Covalent compounds tend to form so that each atom, by sharing electrons,
completes an octet of electrons in its highest occupied energy level.
C. Exceptions to the octet rule:
1. Hydrogen: forms bonds in which it’s surrounded by two electrons
2. Boron: (3 valence electrons) forms bonds in which it’s surrounded by six
electrons
IV. Electron-­‐Dot Notation
A. Definition: an electron-­‐configuration notation in which only the valence electrons
of an atom of a particular element are shown, indicated by dots placed around the
element’s symbol. The inner-­‐shell electrons are not shown.
V. Lewis Structures:
A. Electron dot notation can also be used to represent molecules.
B. Unshared Pairs of electrons (Lone Pairs)
1. A pair of electrons that is not involved in bonding and that belongs
exclusively to one atom
2. represented by two dots
C. Shared pairs of electrons
1. Electrons pairs involved in covalent bonds (shared)
2. represented by dash