Unit 1 – Day 8

1. Unit 1 – Day 8 Naming Covalent Compounds

2. Covalent Compounds • Covalent bonds form when two non-metals share electrons. • When electrons are shared, there is no charge on elements. • Because of this we can NOT use the criss cross method, or roman numerals. • Instead, we use prefixes.

3. To name molecular compounds: A prefix is used to indicate the number of each atom present. Prefix Atoms Example mono 1 carbon monoxide di2 carbon dioxide tri 3 sulfur trioxide tetra 4 carbon tetrafluoride penta5 phosphorus pentabromide hexa6 sulfur hexafluoride

4. Writing Formulas Step 1: Write the symbols of the elements. Step 2: Write the subscript for the number of atoms represented by the prefix. E.g. sulfur trioxide E.g. diphosphorus pentasulfide

5. Which goes first? • With two non-metals, how do you decide which one goes first? • We need to look at a value called “electronegativity” on the periodic table. • Whichever element has the lowest electronegativity will go first. • Example: Circle the correct formula. • Cl2S or SCl2 - NH3 or H3N

6. Practice… Carbon dioxide Phosphorus trichloride Sulfur hexaiodide Nitrogen monoxide

7. Writing Names Step 1: Determine the appropriate prefix for each element. Step 2: Write the prefix and the name of the elements. Change the ending of the second one to –ide. E.g. N2O E.g. BrI

8. Practice… N2O4 CF4 SO2 P2O5

9. Diatomic Elements Some elements are diatomic – they exist naturally as two atomsof the same element bonded together. Hydrogen gas H2 Bromine Br2 Oxygen gas O2 Iodine I2 Nitrogen gas N2 Chlorine gas Cl2 Fluorine gas F2