Naming Molecular Compounds CH 4 methane BCl 3 boron trichloride CO 2 Carbon dioxide All are formed from two or more nonmetals. Ionic compounds generally involve a metal and nonmetal (NaCl)

1. What are the structural differences between ionic and molecular compounds? 2. How do those differences affect their chemical formulas?

The chemical formula for a covalent compound is called a molecular formula; The chemical formula for an ionic compound is called a formula unit. Example: H 2 O is the molecular formula of water Example: NaCl is the formula unit of common table salt

What’s the dif?

A VISUAL look at the difference will help out:

Like any ionic compound, sodium chloride exists as a crystal:

Let’s shrink the ions so we can take a peek inside

The formula unit for sodium chloride is NaCl. However, if we look inside the crystal, the Na + and Cl - ions are each bonded to six oppositely charged neighbors:

Because each Na + is bonded to more than one Cl - ion, and each Cl - is bonded to more than one Na + ion, then

all the ions in the whole crystal are part of one single bonded unit, and the crystal below would be Na 32 Cl 32.

This is impractical, given the enormous numbers of ions in a crystal large enough to see with our eyes. So, only the ratio of ions is given (its empirical formula), which is called a formula unit. NaCl is the formula unit for the sodium chloride crystal. NaCl is the smallest whole number ratio of sodium and chloride ions in the crystal.

What about molecules?

water is covalently bonded hydrogen and oxygen. ‘space filling’ model ‘ball and stick’ model A single water molecule

The H 2 O molecule remains as a single unit of three covalently bonded atoms. The H2O molecule remains as a single unit of covalently bonded molecules

NaCl This difference in structure between molecules and ionic compounds is reflected in their symbols: versus H2OH2O The molecule is represented by a molecular formula, showing all the atoms present in the unit. The ionic compound is represented by the ratio of its ions, which is called a formula unit.

Molecular (Covalent) Nomenclature for two nonmetals  Prefix System (binary compounds) 1.Less electronegative atom comes first. 2.Add prefixes to indicate # of atoms. Omit mono- prefix on the FIRST element. Mono- is OPTIONAL on the SECOND element. 3.Change the ending of the second element to -ide.

PREFIXmono-di-tri-tetra-penta-hexa-hepta-octa-nona-deca-NUMBER Molecular Nomenclature Prefixes

 CCl 4  N 2 O  SF 6 carbon tetrachloride carbon tetrachloride dinitrogen monoxide dinitrogen monoxide sulfur hexafluoride sulfur hexafluoride Molecular Nomenclature: Examples

 arsenic trichloride  dinitrogen pentoxide  tetraphosphorus decoxide AsCl 3 AsCl 3 N 2 O 5 N 2 O 5 P 4 O 10 P 4 O 10 More Molecular Examples

Learning Check 1.P 2 O 5 a) phosphorus oxide b) phosphorus pentoxide c) diphosphorus pentoxide 2.Cl 2 O 7 a) dichlorine heptoxide b) dichlorine oxide c) chlorine heptoxide 3. Cl 2 a) chlorine b) dichlorine c) dichloride

Mixed Practice 1. Dinitrogen monoxide 2. Potassium sulfide 3. Copper (II) nitrate 4. Dichlorine heptoxide 5. Chromium (III) sulfate 6. Iron (III) sulfite 7. Calcium oxide 8. Barium carbonate 9. Iodine monochloride