Organic chemistry 101/11/16 期中考試 102/01/11 期末考試 講義位址
-
date post
21-Dec-2015 -
Category
Documents
-
view
246 -
download
6
Transcript of Organic chemistry 101/11/16 期中考試 102/01/11 期末考試 講義位址
Organic chemistry
• 101/11/16 期中考試• 102/01/11 期末考試
講義位址 http://www.aqua.ntou.edu.tw/chlin/ http://moodle.ntou.edu.tw/
Fundamentals of Organic Chemistry7th Edition McMurryThomson Brooks/Cole
Organic chemistry
Organic chemistry: The study of the compounds of carbon (C)
Over 30 million organic compounds have been identified─about 1000 new ones are discovered or
synthesized and identified each day!
C is a small atom
─ It can share 4 valence electrons and form 4 covalent bonds
─ it can bond to one another and form long chains and rings
─ it is able to form an immense diversity of compounds, from methane to DNA
Atomic structure
• Small dense nucleus, diameter 10-14 - 10-15 m, which made of neutrons and positively-charged protons.
• Most of the mass of the atom is contained in its nucleus.• Extranuclear space, diameter 2 x 10-10 m (0.2 nm, 200 pm, 2Å),
which contains negatively-charged electrons
Electrons do not freely move in the space around a nucleus and are confined to regions of space called principle energy levels
Orbitals• A region of space around a nucleus where electrons are found
• A region of space where an electron or pair of electrons spends 90-95% of its time
• 4 different kinds of orbitals, denoted s, p, d, f........
• All s orbitals have the shape of a sphere
• A p orbital consists of two lobes separated by a node
• Different layers, or electron shells, contain different numbers and kinds of orbitals
• Each orbital can be occupied by 2 electrons • Electrons in lower numbered shells are nearest to the positively
charged nucleus and are held most strongly by it; these electrons are said to be lowest in energy
Electron Configuration of Atoms
The lowest-energy arrangement, or ground-state electron configuration, of an atom is a description of the orbitals that the atom’s electrons occupy• Rule 1: The orbitals of lowest energy are filled first,
according to the order 1s2s2p3s 3p 4s 3d 4p 5s 4d 5p
• Rule 2: Only two electrons can occupy an orbital, and they must be of opposite spin
• Rule 3: If two or more empty orbitals of equal energy are available, one electron occupies each with the spins parallel until all orbitals are half-full
• Gilbert N. Lewis• Valence shellValence shell: the outermost electron shell of an
atom• Valence electronsValence electrons: electrons in the valence shell of
an atom; these electrons are used in forming chemical bonds
• Lewis structure of an atomLewis structure of an atom– the symbol of an element surrounded by a
number of bots equal to the number of electrons in the valence shell of the atom
Lewis structures
Lewis Structure: The symbol of an element surrounded by a number of dots equal to the number of electrons in the valence (outmost) shell of the atom
The Nature of Chemical Bonds
• Atoms bond together so that each atom in the bond acquires the electron configuration of the noble-gas closest it in atomic number
– Octet rule: The tendency to react in ways that achieve an outer shell of eight valence electrons
• Ionic bondIonic bond: a chemical bond resulting from the electrostatic
attraction of an anion and a cation (Na+ Cl-)
– an atom that gains electrons becomes an anion
– an atom that loses electrons becomes a cation
• Covalent bondCovalent bond: a chemical bond resulting from two atoms sharing one or more pairs of electrons
Forming Covalent Bonds:Valence Bond Theory
A covalent bond forms when two atoms approach each other closely and a singly occupied orbital on one atom overlaps a singly occupied orbital on the other
The electrons are now paired in the overlapping orbitals and are attracted to the nuclei of both atoms, thereby bonding the atoms together
Hybridization:sp3 Orbitals and the Structure of Methane Carbon has four electrons in its valence shell (2s2
2p2) An s orbital and three p orbitals can combine, or
hybridize, to form four equivalent atomic orbitals (sp3 hybrids) with tetrahedral orientation
Hybridization:sp3 Orbitals and the Structure of Ethane
Bond strength of C-H: 421 kJ/mol
Bond strength of C-C: 377 kJ/mol
Hybridization:sp2 Orbitals and the Structure of Ethylene
An s orbital combines with only two of three p orbitals to form three equivalent atomic orbitals (sp2 hybrids)
One unhybridized 2p orbital remains unchanged
Hybridization:sp Orbitals and the Structure of Acetylene
An s orbital combines with only one of three p orbitals to form three equivalent atomic orbitals (sp hybrids)
Two unhybridized 2p orbital remains unchanged
Polar Covalent Bonds:Electronegativity
• A molecule is polar if 1. It has polar bonds and
2. The center of partial positive charge lies at a different place within the molecule than the center of partial negative charge
ElectronegativityElectronegativity: a measure of the force of an atom’s attraction for the electrons it shares in a chemical bond with another atom
Acids and Bases:The Bronsted-Lowry Definition
HA + H2O A- + H3O+
Ka = [A-] + [H3O+]
[HA] pKa = -logKa
Acids and Bases:The Lewis Definition
• A Lewis acid is a substance that has a vacant valence orbital and can thus accept an electron pair
• A Lewis base is a substance that donates an electron pair
• The donated pair of electrons is shared between Lewis acid and base in a newly formed covalent bond