A.5 Chemical Bonding: Introduction Organic chemistry is study of hydrocarbons and their derivatives Up until 150 years ago scientists thought only life could create hydrocarbons Carbon atoms are joined into carbon chains Hydrogen atoms are attached to the chain Carbon is very versatile at bonding

A.5 Chemical Bonding: Electron Shells Electrons are key to bonding atoms Electrons occupy energy levels around the nucleus. Energy levels are grouped into shells Each shell holds up to a certain # electrons (2n 2 : first shell 2, second 8, third 18,…) Atoms with full shells are chemically unreactive or stable (2 [He], 10 [Ne] electrons, etc) (Noble Gases)

A.5 Chemical Bonding: Covalent Bonds In molecular (non-ionic) substances electron gains are achieved by sharing Two hydrogen atoms make a great example: H. +.H  H:H (notation is electron-dot or Lewis structure) This chemical bond is called a single covalent bond – two atoms share a pair of electrons. Only outer shell electrons participate in chemical reactions

A.5 Chemical Bonding: Covalent Bonds (continued) H... | 4 H. +.C.  H:C:H  H-C-H... | H H (structural formula) AKA: CH 4

A.5 Chemical Bonding: Boiling Points The greater the number of carbons the stronger the intermolecular/attractive forces and the higher the boiling point Adding one CH 2 increases BP by 30 C Methane: , Ethane

A.6 Modeling Alkanes Methane, CH 4 is the simplest hydrocarbon 1 st in the series of hydrocarbons called alkanes Each carbon atom in an alkane forms single covalent bonds with 4 other atoms

A.5,6 Chemical Bonding: Alkane Series and Boiling Points Boiling ShortLong Name Point (C)#Carbon formula Methane-1621 CH 4 Ethane C2H6C2H6 CH 3 Propane C3H8C3H8 CH 3 CH 2 CH 3 Butane-0.54 C 4 H 10 CH 3 CH 2 CH 2 CH 3 Pentane36.15 C 5 H 12 CH 3 CH 2 CH 2 CH 2 CH 3 Hexane68.76 C 6 H 14 CH 3 CH 2 CH 2 CH 2 CH 2 CH 3 Heptane98.47 C 7 H 16 CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 Octane C 8 H 18 CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 Nonane C 9 H 20 CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 Decane17410 C 10 H 22 CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 Etc…

A.7 Alkanes Revisted: Branched-chain alkanes have 1 or more carbon atoms liked to 3 to 4 others Isomers are molecules with identical formulas, but different arrangement of atoms Each Isomer is a different structure so it has different properties – the more spherical (caused by branches) the lower the boiling point due to the molecules having a lower intermolecular attraction. (Less contact with other molecules)