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Organic ChemistryChapter 11.1LIFE AND THE CHEMISTRY OF CARBON COMPOUNDS—WE ARE STARDUSTOrganic chemistry is the chemistry of compounds that contain the element carbon. Carbon compounds are central to the structure of living organisms and therefore to the existence of life on Earth. We exist because of carbon compounds. 1.1ATOMIC STRUCTUREThe compoundswe encounter in chemistry are made up of elementscombined in different proportions. Elements are made up of atoms. An atom consists of a dense, positively charged nucleus. Nucleus contains protons and neutronsand a surrounding cloud of electrons. Protons have a positive charge (+) Electrons have a negative charge (-) Neutrons are electrically neutralProtons and neutrons contain nearly equal masses. Mass of an atom comes from the nucleus. The volume of the atom comes from the electrons. Elements commonly found in organic molecules are: oCarbon oHydrogen oNitrogen oOxygen oPhosphorus oSulfur oAnd some halogens: fluorine, chlorine, bromine and iodine. Each elementis distinguished by its atomic number (Z), a number equal to the number of protons in its nucleus. The atomic number also equals the number of electrons surrounding the nucleus. 1.2A ISOTOPESThe existence of atoms of the same element that have different masses. Mass= protons + neutron (protons is the atomic number, which is the same as the neutrons) Although all the nuclei of all atoms of the same element will have the same number of protons, some elements may have different masses because of the different number of neutronsIsotopes1.2B VALENCE ELECTRONSElectrons that surround the nucleus exist in shellsEach shell increases in energy and increases the distance from the nucleus Most important shell=valence shell Valence Shell: the outermost shell because electrons of this shell are the ones that an atom uses in making chemical bonds with other atoms to form compounds. The number of electron in the valence shell is equal to the group number of the atom. 1.2CHEMICAL BONDSIonic bonds: are formed by the transfer of one or more electrons from one atom to another to create ions. Covalent bonds:result when atoms share electrons. Octect Rule:tendency for an atom to achieve a configuration where its valence shell contains 8 electrons. 1.3A IONIC BONDSAtoms may gain and lose electrons and form charged particles ions. An ionic bond: attractive force of opposite charged ions. Electronegativity: measure of the ability of an atom to attract electrons. oIncreases as you go across a horizontal row. Saltsonly form when atoms of very different electronegativities transfer electrons to become ions.
1.3B COVALENT BONDS AND LEWIS STRUCTURESCovalent bonds: form by sharing of electrons between atoms of similar electronegativities to achieve the configuration of a noble gas.