THE BEST SCIENTIST IS OPEN TO EXPERIENCE AND BEGINS WITH ROMANCE - THE IDEA THAT ANYTHING IS POSSIBLE. - Ray Bradbury – DON’T SAY YOU DON’T HAVE ENOUGH TIME. YOU HAVE EXACTLY THE SAME NUMBER OF HOURS PER DAY THAT WERE GIVEN TO HELEN KELLER, PASTEUR, MICHAELANGELO, MOTHER TERESEA, LEONARDO DA VINCI, THOMAS JEFFERSON AND ALBERT EINSTEIN. - H. Jackson Brown, Jr.-

VSEPR THEORY ALLOWS US TO PREDICT MOLECULAR GEOMETRIES BASED ON THE NUMBER OF ELECTRON DOMAINS A BONDING ATOM HAS. TO FURTHER EXPLAIN HOW ATOMS BOND TO FORM MOLECULES, CHEMISTS USE THE VALENCE BOND THEORY. THE VALENCE BOND THEORY SAYS THAT ATOMIC ORBITALS FROM ADJOINING ATOMS CAN OVERLAP TO FORM BONDS. TO EXPLAIN ALL OF THE BOND ANGLES AND SHAPES THAT RESULT, THIS THEORY SAYS THAT INDIVIDUAL ATOMIC ORBITALS CAN AVERAGE OUT OR HYBRIDIZE TO GIVE DIFFERENT SHAPES.

mistry/flash/hybrv18.swf

CARBON CHEMISTRY Atomic Number 6 Atomic Mass Average: Melting Point: 3823 K (3550°C or 6422°F) Boiling Point: 4098 K (3825°C or 6917°F) Density: 2.267g/cu.cm. CARBON HAS FIVE KNOWN ALLOTROPES: AMORPHOUS GRAPHITE DIAMOND FULLERENE MAGNETIC CARBON NANOFOAM NOTE: TUNGSTEN HAS THE HIGHEST MELTING POINT OF ANY METAL AT 3422 o C. IRON HAS A MELTING POINT OF 1535 o C.

protonsneutronsmass number carbon carbon carbon ISOTOPES OF CARBON

CARBON DATING THE AMOUNT OF 14 C REMAINS APPROXIMATELY CONSTANT IN THE ATMOSPHERE BECAUSE 14 C IS BEING FORMED IN THE UPPER ATMOSPHERE THROUGH NEUTRON CAPTURE N + 1 n  14 6 C + 1 p CARBON-14 DECAYS WITH A HALF LIFE OF 5715 YEARS C  14 7 N + 0 e WE ASSUME THAT THE RATIO OF CARBON 14 TO CARBON 12 HAS BEEN CONSTANT FOR AT LEAST 50,000 YEARS.

ATOMIC STRUCTURE OF CARBON THIS MEANS THAT CARBON HAS FOUR VALENCE ELECTRONS.

The electronegativity (EN = 2.55) is too small to allow carbon to form C 4- ions and too large to allow carbon to form C 4+ ions. Carbon forms covalent bonds. To reach inert gas configuration, it needs a share in 4 more electrons. It can do this several ways. One 2s electron can shift up to the vacant 2p orbital. These orbitals can hybridise to give 4 sp 3 hybrids. This would allow it to form 4 covalent bonds (sigma bonds) with 4 other elements.

HYBRIDIZATION OF 3 P ORBITALS AND 1 S ORBITAL TO GIVE 4 SP 3 HYBRID ORBITALS.

A SIGMA BOND IS A BOND FORMED WHEN ONE PAIR OF ELECTRONS IS SHARED BETWEEN TWO ATOMS. IN THE CASE OF FOUR SP 3 HYBRID ORBITALS, FOUR SIGMA BONDS COULD BE FORMED WITH FOUR OTHER ATOMS. To be equi-distant from each other, these bonds would be pointing to the corners of a regular tetrahedron, and the bond angles would be o. An example would be methane.

HERE ARE THREE WAYS OF REPRESENTING THE MOLECULE METHANE.

SPACE FILLING MODEL

ONE ALLOTROPE OF CARBON THAT USES SP 3 HYBRID BONDING IS DIAMOND. ONE CARBON ATOM IS BONDED TO FOUR OTHER CARBON ATOMS. THIS PROVIDES A VERY STRONG STRUCTURE, MAKING DIAMOND THE HARDEST MATERIAL KNOWN.

Another way carbon can form bonds is for one 2s electron can shift up to the vacant 2p orbital. One electron in the 2s orbital and 2 electrons in two of the 2p orbitals can hybridise to form three sp 2 hybrid orbitals. For these three orbitals to be equidistant, they would be trigonal planar. All would be in the same plane, and the bond angles would be 120 o. The remaining electron would be in a 2p orbital at right angles to the plane that the hybrid orbitals occupied.

THIS IS THE TYPE OF BONDING THAT WOULD BE USED IN GRAPHITE.

THE SAME KIND OF BONDING WOULD BE USED IN FULLERENES. A C60 FULLERENE

Creative Chemistry Interactive Molecular Models - Carbon Allotropes

THE FINAL WAY CARBON CAN BOND WOULD BE FOR ONE 2S ELECTRON TO SHIFT UP TO THE VACANT 2P ORBITAL. THEN, 1 ELECTRON IN ONE OF THE 2P ORBITALS COULD HYBRIDISE WITH 1 ELECTRON IN THE 2S ORBITAL TO FORM TWO SP HYBRID ORBITALS. FOR THESE ORBITALS TO BE EQUIDISTANT, THEY WOULD BE PLANAR AND 180 O APART. THE TWO REMAINING 2P ELECTRONS WOULD BE IN 2P ORBITALS AT RIGHT ANGLES TO THE SP HYBRID OBRITALS.

TWO SP HYBRID ORBITALS WITH TWO 2P ORBITALS.

SP BONDING IS NOT USED IN THE FORMATION OF ANY CARBON ALLOTROPES. IT IS USED IN FORMATION OF SOME COMPOUNDS CONTAINING CARBON. THE TABLE BELOW COMPARES THE PROPERTIES OF GRAPHITE AND CARBON - TWO ALLOTROPES OF CARBON THAT USE DIFFERENT HYBRIDIZATION.

Indeed, diamonds do burn. However, since they're pure carbon, and in the burning process are converted to carbon dioxide (only), there is no ash residue whatever. Had an interesting thing occur once when a home burned down and a rather "costly" jewelry piece was lost. It turned out that what was thought to be a diamond was found amid the melted gold remains of the setting. The stone was completely intact and undamaged. It was later discovered to be a cubic zirconia (fake diamond) that would not burn. The fellow's wife was not impressed that her husband would have fooled her into thinking he had spent big money on a diamond when he had actually bought her a vastly less expensive cubic zirconia. Regards, ProfHoff

GRAPHITE IS THE STABLE ALLOTROPE AT ROOM TEMPERATURE. In 1955 GE developed a process to make industrial diamonds. Graphite is heated in the presence of a metal catalyst at temperatures of from 2000 to 3000 K and pressures of 125,000 atm.

BONDING POSSIBILTIES FOR CARBON THESE BONDING POSSIBILITIES ALLOW CARBON TO FORM SEVERAL TYPES OF BONDS WITH OTHER CARBON ATOMS AND WITH OTHER ELEMENTS.

THERE IS AN ENTIRE BRANCH OF CHEMISTRY DEVOTED TO THE CHEMISTRY OF CARBON COMPOUNDS - ORGANIC CHEMISTRY. THERE ARE SEVERAL BRANCHES OF ORGANIC CHEMISTRY: 1)BIOCHEMISTRY - THE CHEMISTRY OF LIVING ORGANISMS 2)POLYMER CHEMISTRY - THE CHEMISTRY OF VERY LARGE MOLECULES OF REPEATING STRUCTURE 3)ORGANIC SYNTHESIS - THE SCIENCE OF BUILDING MOLECULES OF GIVEN STRUCTURES 4)ORGANIC ANALYSIS - COMPOSITION AND STRUCTURE DETERMINATION

hang_7e_esp/bom5s2_6.swf THIS LINK DISCUSSES SIGMA AND PI BONDS.