Wednesday, Sept. 4, 2013
Chemistry of Water and Carbon
BIO13L - JF, MM, KM
Overview of today’s topics:
(Chapter 2: sections 2.2, 2.3, 2.5)
Bioskills 6&8 in Appendix
1. Atomic Structure:
2. Electron Orbitals, Chemical Reactivity, and
3. Covalent and Ionic Bonds
4. Polarity of Water, Acids and Bases
Atomic number (number of electrons)
Electrons occupy orbitals (2 e in every orbital), and orbitals are grouped into electron shells:
Shell 1: 1 s orbital (2 e
Shell 2: 1 s orbital and 3 p orbitals (8 e
Shell 3: 1 s orbital, 3 p orbitals and 5 d orbitals (18 e
The lower the shell number, the closer to the nucleus and the lower the energy.
1 Chemical reactivity is largely driven by the fact that atoms are most stable when
they have a filled outer shell of electrons (the noble gas configuration).
The number of unpaired electrons in the outer shell is the valence.
shells through electron sharing.
– Nonpolar covalent bonds have equal sharing
– Polar covalent bonds have unequal sharing
COVALENT BONDS (sharing of electrons)
The electrons spend some of their time around each
atom giving each H atom the stable 2e filled orbital.
2 Each single line represents two shared electrons
Carbon with 4 single bonds is tetrahedral because the s and 3p orbitals hybridize to
create 4 hybrid orbitals of equal energy for the second shell.
Five e- in outer shell.
Six e- in outer shell
Will form three
covalent bonds and Will form two
has a lone pair of covalent bonds and
has two filled
that can pick up a free orbitals that can
proton (H ) from work as H-bond
solution or act as an H- acceptors
The geometry of bonds is dictated by the configuration of orbitals, including
those that do not participate in the bonds.
3 Polar bonds occur because the two atoms in
the bond have different electronegativity.
H –2.2 C –2.5 N –3.0 O –3.5 F –4.0
P –2.2 S –2.5 Cl –3.0
Electronegativity is a function of valence and
shielding of the valence electrons by shells of
Electronegativity of O = 3.5; electronegativity of H = 2.2
4 Practice question
Which molecule has the bonds which are most polar ?
1. H 2O
2. H 2
3. CH 4
4. NH 3
Properties of Water