Review Info Survey of Organic Chemistry FINAL Study Guide Endothermic A process or reaction that absorbs heat and has a positive DeltaH When the total strength of the bonds formed in the products is greater than the total strength of the bonds broken in the reactants energy is released and a reaction is exothermic Exothermic A process or reaction that releases heat and has a negative DeltaH When the total strength of the bonds formed in the products is greater than the total strength of the bonds broken in the reactants energy is released and a reaction is exothermic Law of Conservation of Energy Energy can neither be created nor destroyed in any physical chem change Enthalpy DeltaH energy of bonds formed in the products minus energy of bonds broken in reactants Spontaneous Process is one that once started proceeds on its own without any external in uence Entropy the amount of disorder in a system DeltaS The greater the disorder randomness of the particles in a substance mixture the larger the value of S DeltaS disorder increases because the process adds disorder to the system Example melting ice into water The group of atoms held together by covalent bonds is called a molecule DeltaS the disorder of a system decreases Example the freezing of water Free energy change determines the spontaneity DeltaG DeltaG free energy is added process is endergonic DeltaG free energy is released process is exergonic Electron sharing typically occurs when a singly occupied valence orbital on one atom overlaps a singly occupied valence orbital on another atom The two electrons occupy both overlapping orbitals and belong to both atoms thereby bonding the atoms together Alternatively electron sharing can occur when a lled orbital containing an unshared lone pair of electrons on one atom overlaps a vacant orbital on another atom to form a coordinate covalent bond A covalent bond is formed by the sharing of electrons between atoms rather than by complete transfer of electrons Ch 5 Summary from one atom to another Atoms that share two electrons are joined by a single bond such as C C atoms that share four electrons are joined by a double bond C C atoms that share six electrons are joined by a triple bond The group of atoms held together by covalent bonds is called a molecule Electron sharing typically occurs when a singly occupied valence orbital on one atom overlaps a singly occupied valence orbital on another atom The two electrons occupy both overlapping orbitals belong to both atoms thereby bonding the atoms together Alternatively electron sharing can occur when a lled orbital containing an unshared lone pair of electrons on one atom overlaps a vacant orbital on another atom to form a coordinate covalent bond Depending on the number of valence electrons different atoms form different numbers of covalent bonds In general an atom shares enough electrons to reach noble gas con guration Hydrogen for instance forms one covalent bond because it needs to share one more electron to achieve helium con guration 1s2 Depending on the number of valence electrons different atoms form different numbers of covalent bonds In general an atom shares enough electrons to reach noble gas con guration Hydrogen for instance forms one covalent bond because it needs to share one more electron to achieve helium con guration 1s2 Carbon and other group 4A elements form four covalent bonds because they need to share four more electrons Carbon and other group 4A elements form four covalent bonds because they need to share four more electrons to reach an octet In the same way nitrogen and other group 5a elements form 3 covalent bonds oxygen and other group 6A elements form two covalent and halogens groups 7a elements form one covalent bond atoms and valence electron lone pairs are shown as dots Lewis structures are drawn by counting the total number of valence electrons in a molecule or polyatomic ion and then placing shared pairs bonding and lone pairs nonbonding so that all electrons are accounted for Formulas such as H2O NH3 and CH4 which show the numbers and kinds of atoms in a molecule are called molecular formulas More useful are lewis structures which show how atoms are connected in molecules Covalent bonds are indicated as lines between atoms and valence electron lone pairs are shown as dots Lewis structures are drawn by counting the total number of valence electrons in a molecule or polyatomic ion and then placing shared pairs bonding and lone pairs nonbonding so that all electrons are accounted for Molecules have speci c shapes that depend on the number of electron charge Molecules have speci c shapes that depend on the number of electron charge clouds bonds and lone pairs surrounding the various atoms These shapes can often be predicted using the VSEPR model Atoms with 2 electron charge clouds adopt linear geometry atoms with 3 charge clouds adopt planar triangular geometry and atoms with 4 charge clouds adopt tetrahedral geometry clouds bonds and lone pairs surrounding the various atoms These shapes can often be predicted using the VSEPR model Atoms with 2 electron charge clouds adopt linear geometry atoms with 3 charge clouds adopt planar triangular geometry and atoms with 4 charge clouds adopt tetrahedral geometry Molecules have speci c shapes that depend on the number of electron charge clouds bonds and lone pairs surrounding the various atoms These shapes can often be predicted using the VSEPR model Atoms with 2 electron charge clouds adopt linear geometry atoms with 3 charge clouds adopt planar triangular geometry and atoms with 4 charge clouds adopt tetrahedral geometry Bonds between atoms are polar covalent if the bonding electrons are not shared equally between the atoms The ability of an atom to attract electrons in a covalent bond is the atoms electronegativity and is the highest for reactive nonmetal elements on the upper right of the periodic table and the lowest for metals on the lower left Bonds between atoms are polar covalent if the bonding electrons are not shared equally between the atoms The ability of an atom to attract electrons in a covalent bond is the atoms electronegativity and is the highest for reactive nonmetal elements on the upper right of the periodic table and the lowest for metals on the lower left Comparing electronegativities allows a prediction of whether a given bond is covalent polar covalent or ionic Just as individual bonds can be polar entire molecules can be polar if