Today’s goals Learn the naming system for molecules—covalently bonded substances. Memorize the prefixes necessary to describe the number of atoms in each molecule. Apply to naming of formulas.

Homework Review

Ionic or molecular? KCl NO3 KClO3

Naming Molecular Compounds Before we do this there is a small matter of exceptions to the rules in ionic naming. Mercury—always appears as two. Peroxide—always two. H2O2 H in front is a + so is an acid—we will name those later. H on the right is a negative ion, so is a “hydride”. So H can be both.

Naming Molecular Compounds This system is a little bit different. It is used when non metals combine. Since there is no way to tell how many atoms combine we simply tell you in the name. However, to let you know it is molecular, we use a different system for one, two three etc.

The numbering system No Roman Numerals are used. We have abbreviations for 1-10, called prefixes that are used in front of the name. 1. mono 6. hexa 2. di 7. hepta 3. tri 8. octa 4. tetra 9. nona 5. penta 10. deca Binary compounds still end in “ide”. There are some exceptions: mono is not used in front of compounds. No names start with “mono”.

To Name: 1. Use the name of the first element. Put a prefix in front unless there is only one atom. Change the second name to end in “ide” Use a prefix!! Examples: N2O dinitrogen monoxide PCl3 phosphorus trichloride SF6 sulfur hexaflouride

There’s no plus or minus….so who goes first? The element with the lower group goes first. Example: Nitrogen and oxygen combine. Put nitrogen first---NO2 Exception!!! With oxygen and a halogen, the halogen goes first. Ex chlorine dioxide. ClO2 If you are in the same group, the element with the higher period goes first.

Name it!! CO2 N2O5 SF6 SO3 S2Cl2 Si3N4 carbon dioxide dinitrogen pentoxide sulfur hexaflouride sulfur trioxide disulfur dichloride trisilicon tetranitride

Exceptions to the “rules” Some compounds have common names we use instead of their chemical names. Water---H2O (dihydrogen monoxide) Ammonia—NH3 (nitrogen trihydride) Methane—CH4 (carbon tetrahydride) Sugar—C6H12O6 (hexacarbon ??? Now you see)

Let’s practice!!