Formula Writing Say what??

Formula Writing Ionic Compounds One metal + one non-metal

Let’s Review Fill in the charges

More Review How are ions formed? Positive ions – Aka: Negative ions –

Lets Write Some Formulas… Positive ions are ALWAYS written first. If more than one ion can exist, use parentheses and the charge in roman numeral form Ie: Cu+2 is named copper (II) These are called multivalent ions. Negative ions are ALWAYS written second. So… Can two positive ions ever be put together? Can two negative ions ever be put together?

How do you know what numbers to use? Criss-Cross Method Identify the charge of each ion “criss-cross” the charges  ignore the + and – Numbers become subscripts for other element Let’s do a few examples… pick any cation and anion:

Naming Compounds Cation stays the same Anion ending changes to –ide Often this simply involves changing the –ine ending Chlorine  chloride Fluorine  fluoride Bromine  bromide However, there are some you need to remember: Examples: Phosphorus  phosphide Sulfur  sulfide Oxygen  oxide

Let’s do some more practice… Charges Criss Cross Name Ca and Cl Ba and O Cu and I

Formula Writing Polyatomic Ion Compounds

Polyatomic Ions Remember: New: Cation (positive ion) is written first Anion (negative ion) is written second New:   Put parentheses around the polyatomic ion ALWAYS

Naming the Compounds with Polyatomics You need to recognize the Polyatomic Ions If monoatomic ion: cation and anion is the same If polyatomic ion: use names provided

Some Polyatomic Practice Write the formula the following: Formula Name  Ba +2 C2H3O2 -1 ________________ _____________________ Al +3 PO4 -3 ________________ _____________________  K +1 SO4 -2 ________________ _____________________ Ca +2 NO3 -1 ________________ _____________________

Formula Writing Covalent Molecules 2 non-metals together

Writing Formulas Remember, bonds require 2 electrons Covalent is the sharing of electrons

Naming Covalent Compounds The less electronegative element is written first. Remember the trend (increasing up and to the right) Use a number indicating prefix only if more than one atom is present Ie N2 is dinitrogen A prefix is always added to the name of the second element Will change ending of name to –ide (just like ionic bonds)

Naming Covalent Compounds - Rules 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. Number Indicating Prefixes: mon(o) -1 hex(a) - 6 di -2 hept(a) - 7 tri -3 oct(a)- 8 tetr(a) - 4 non(a) -9 pent(a) -5 dec(a) -10

Try Some Practice N2S4 NI3 CCl4 P2O5

Try Some Practice ~ ANSWERS NI3 CCl4 P2O5 Dinitrogen tetrasulfide Nitrogen triiodide Carbon tetrachloride Diphosphorus pentoxide

Common Names H2O - water NH3 - ammonia CH4 - methane C2H6 - ethane C3H8 - propane