有机化学双语课件Chpt_1

•Wöhler’s Synthesis of Urea:
•Synthesis –Construct complex organic chemicals from simpler, more readily available ones (Chapter 8).
covalent bond is formed.
Ionic Bonds are based on the transfer of one or more
electrons from one atom to another. The resulting cation
and anion are electrostatically attracted to each other.
metal that of the preceding inert gas, the halogen that of
valence electrons:
Hydrogen can either lose an electron to form an H
an electron to form a H-, or hydride, ion:
configuration.
•In certain cases, one atoms supplies both of the electrons
in the bond:
•Often 4 electron (double) and 6 electron (triple) bonds are
formed:
•As a rule of thumb, electronegativity differences less
than 0.3 represent pure covalent bonds, from 0.3 to 2.0
polar covalent bonds, and greater than 2.0 ionic bonds.
•The separation of opposite charges in polar covalent
molecules results in the formation of dipoles:
Correct Lewis Structure Incorrect Lewis Structures
satisfy the octet rule:
½(# bonding electrons surrounding the atom)
In molecules such as nitric acid, charges occur on
individual atoms, even though the molecule itself is
neutral.
The 2 negative charges are delocalized over all three
Structures with a maximum of octets are most
Charges should be preferentially located on atoms with
electronegativity. If this conflicts with rule
1, then rule 1 takes precedence.
more important resonance contributors than those with
1 takes precedence over guideline 2:
If there are two or more charge separated resonance
structures which comply with the octet rule, the most
producing either constructive or destructive interference:
called s orbitals. The lowest energy s orbital is the 1s orbital.contains a spherical nodal surface.
Of slightly higher energy than the 2s orbital are 3 degenerate 2p orbitals. These orbitals are shaped like a figure 8 and point along the 3 Cartesian axes.
Aufbau principle assigns electrons to
Lower energy orbitals are filled before those with higher
No orbital may be occupied by more than two electrons. ( Exclusion Principle). If two electrons occupy a single orbital,
configuration.
The process of filling up the energy level diagram one electron at a time is called the Aufbau process.
The d orbitals on atoms of row 3 and higher are involved in the formation of expanded octets(10 and 12 electrons about
orbital places most of the electron probability to the left and right of
with the observed bond angle in the BeH2molecule.
Hybridization does not change the number of orbitals on
the atom. In this case two atomic orbitals are replaced by
two new hybrid orbitals. The two un-hybridized p orbitals
are still available to hold electrons.
approximately 109.5 approximately 120
The molecule, BH3is isoelectric with the methyl cation, CH3+.
Both involve sp2hybridization about the central atom.
contain lone pairs of electrons.
The bond angles in ammonia are 107.3o and that in water is
104.5o, both close to 109.5o. The slightly smaller bond
angles in ammonia and water are due to the slightly larger
volume requirements for lone pair electrons, which forces the
connectivity of atoms are called constitutional or structural
molecular structures.。