Molecular Compounds

Molecular Compounds Composed of all nonmetals Single unit = Molecule Held together by covalent bonds Atoms share pairs of electrons They can share 1, 2, or 3 pairs of electrons to form single, double or triple covalent bonds.

Molecular Compounds Two of the same elements can combine in different ratios to form different molecular compounds. Ex. Carbon dioxide = CO2 Carbon monoxide = CO

Examples of Molecular Compounds Common Names H2O, water NH3, ammonia CH4, methane C2H6, ethane C3H8, propane C6H12O6, glucose C8H10N4O2, caffeine C6H8O6, ascorbic acid (vitamin C)

Organic Compounds and Hydrocarbons A molecule primarily made from carbon and hydrogen, but often with some oxygen, nitrogen, or some other nonmetal element. Ex. Ethanol = C2H5OH Hydrocarbon: An organic compound that contains only hydrogen and carbon atoms. Ex. Paraffin Wax = C20H42

Prefixes 1 = 2 = 3 = 4 = 5 = 6 = 7 = 8 = 9 = 10 =

Naming & Writing Formulas for Binary Molecular Compounds Prefixes = Subscripts Add prefixes to beginning of element’s name to indicate # of atoms in a molecule Use –ide ending on second element

Naming & Writing Formulas for Binary Molecular Compounds If the subscript for the first element is greater than one, indicate the subscript with a prefix. We do not write mono- on the first name. Leave the "a" off the end of the prefixes that end in "a" and the “o” off of mono- if they are placed in front of an element that begins with a vowel (oxygen or iodine).

Examples: Name the following: NO2 N2O P2Cl3 SF6 Answers: Nitrogen dioxide Dinitrogen monoxide Diphosphorus trichloride Sulfur hexafluoride

Learning Check: Write the formulas: CO2 S2F4 C6H8 P2O8 SO3 Carbon dioxide Disulfur tetrafluoride Hexacarbon octahydride Name the following compounds: P2O8 SO3 C4H7 CO2 S2F4 C6H8 Diphosphorus octoxide Sulfur trioxide Tetracarbon heptahydride

Covalent Bonds A link between atoms due to the sharing of two electrons. This bond forms between atoms of two nonmetals. There are two types of covalent bonds: Polar Covalent Bonds Nonpolar Covalent Bonds The type of bond formed is dependent on the difference between the electronegativities of the elements forming the compounds.

Differences in Electronegativity Bond Type Electronegativity Difference Ionic Bond > 1.67 Polar Covalent Bond 0.3 – 1.67 Non-polar Covalent bond 0.0 – 0.3

Ionic, Polar or Nonpolar? HF H2O NH3 Cl2 CO2

Non-polar Covalent Bonds The electrons are shared equally, there is a even distribution of the negative charge for the electrons in the bond, so there is no partial charges on the atoms.

Polar Covalent Bonds One atom in the bond attracts electrons more than the other atom, the electron negative charge shifts to that atom giving it a partial negative charge. The other atom loses negative charge giving it a partial positive charge.

Polar Covalent Bonding d+ means a partially positive d- means a partially negative d+ d- H Cl The Cl pulls harder on the electrons The electrons spend more time near the Cl

Hydrogen Bonding in Water The slightly negative regions of one molecule are attracted to the slightly positive regions of nearby molecules, forming a hydrogen bond. Each water molecule can form hydrogen bonds with up to four neighbors.