Unit 6: Writing and Naming Chemical Formulas CHEMISTRY I

Ions & The Octet Rule

Vocabulary  Ion – an atom or bonded group of atoms with a positive or negative charge  Anion – a negatively charged ion  Cation – a positively charged ion  Octet Rule – “atoms lose, gain, or share electrons in order to acquire the stable electron configuration of a noble gas”

Ion  An ion is an atom or group of atoms that has either a positive or negative charge

Atoms form ions by gaining or losing electrons  Atoms gain or lose electrons to become stable  An atom is stable when the valence shell is full

Cations – Positive Ions  Sodium loses one electron to become stable  Results in an ion that has a positive charge

Cations  The symbol “+” is written as a superscript to indicate that the sodium has a charge of 1+ Na +

Anions – Negative Ions  Chlorine gains one electron to become stable  Results in an ion with a negative charge

Anion  The symbol “-” is written as a superscript to indicate that the chlorine ion has a charge of 1- Cl -

The Octet Rule  Both ions have a full valence shell containing the maximum number of electrons possible (8)  This new arrangement of valence electrons has less energy than the previous arrangement and is stable Na + Cl -

Noble Gases  A metal atom that has lost electrons (cation) and a nonmetal atom that has gained electrons (anion) will have the same number of electrons as its nearest noble gas.

Common Charges

Naming Ions  Cations: A metal that has lost electrons to become an ion has the same name as the element  Ca 2+ = calcium ion  Anions: A nonmetal that has gained electrons to become an ion has the same name as the element but with the ending changed to –ide  S 2- = sulfide ion  Nitrogen  NitridePhosphorous  Phosphide  Oxygen  OxideFlourine  Flouride

Roman Numerals for Multivents  Multivents – an element that can form an ion in more than one way  Naming: Always include the ion charge as Roman numerals in brackets  Cu + copper (I)“copper one”  Cu 2+ copper (II)“copper two”

Transition Metals to Know  Scandium column: always +3, no Roman numeral needed  F-block: always +3, no Roman numeral needed  Ag: always +1, no Roman numeral needed  Cd & Zn: always +2, no Roman numeral needed  Sn & Pb: either +2 or +4

Charges  Oxidation Number  An oxidation number is the positive or negative charge of an ion ElementOxidation #  Li+1  Be+2  O-2  F-1

Polyatomic Ions

Writing and Naming Ionic Compounds

Ionic Compounds  Cation + anion  Name the cation first (typically a metal) just as it appears on the periodic table  Na + = Sodium  Ca +2 = Calcium

Ionic Compounds  Write the anion next (typically a nonmetal)  Change the ending to –ide  **If the anion is a polyatomic ion, the name stays the same**

Practice  NaClSodium Chloride  AlCl 3 Aluminum Chloride  Na 2 OSodium Oxide  Al 2 O 3 Aluminum Oxide

How to determine the Oxidation Number of Transition Metals  Identify the metal as a Transition with multiple oxidation numbers (ex. Fe)  Uncross the “criss-cross”  If nothing to uncross, identify the charge of the anion. The charges have been simplified  Transition metals will be the same just + Fe 2 O FeS Iron (III) Oxide Iron (II) Sulfide

Practice  CuO  Name: Copper (II) Oxide

Writing Ionic Formula  Identify the ions and their charges  Criss-Cross the charges  The sum of the oxidation numbers must equal zero, so by writing the subscripts we are able to balance the charge  Example: Calcium Chloride  Ions: Ca +2 and Cl CaCl  Formula = CaCl 2  (Don’t write 1’s)

Practice  Magnesium Oxide  Copper (I) Phosphide  Mg 2 O 2 **Simplify to MgO  Cu 3 P

Polyatomic Ions  You can’t change the subscripts in Polyatomic Ions  Put the Polyatomic Ion in brackets and place the subscripts outside those Calcium Phosphate Ca +2 PO 4 3- Ca 3 (PO 4 ) 2

Naming Covalent Compounds

What’s the difference between covalent and ionic?  Ionic compounds have a metal and a nonmetal, a cation and an anion  Covalent compounds are called molecules  They are made from elements that are similar in electronegativity

Covalent Naming uses Prefixes 1. Mono 2. Di 3. Tri 4. Tetra 5. Penta 6. Hexa 7. Hepta 8. Octa 9. Nona 10. deca

Rules  If you have more than one atom of that element in the compound, you will need a prefix before it’s name.  Always put a prefix before the name of the second element  Change the ending of the second element to -ide  P 2 O 5  Diphosphorous pentoxide  CO  Carbon monoxide

Practice  OF 2  SO 2  SO 3  N 2 O 5  N 2 O 4  H 2 O  Oxygen diflouride  Sulfur dioxide  Sulfur trioxide  Dinitrogen pentoxide  Dinitrogen tetroxide  Dihydrogen monoxide

Names and Formulas of Common Acids and Bases

Naming Acids  Acids are almost always compounds made from hydrogen and an anion  Hydrogen + Halogen = hydro________ic acid  HCl = hydrochloric acid  Hydrogen + Polyatomic ion –ate = _______ic acid  HNO 3 = nitric acid  Hydrogen + Polyatomic ion –ite = _______ous acid  H 2 SO 3 = sulfurous acid

Naming Bases  Bases are almost always compounds made from hydroxide (HO - ) and a cation  Cation + Hydroxide  Mg(OH) 2 = Magnesium Hydroxide  LiOH= Lithium Hydroxide

Practice  Hydroiodic acid  HBr  H 2 CO 3  Lead (II) Hydroxide  Sn(OH) 4  Zn(OH) 2  HI  Hydrobromic Acid  Carbonic Acid  Pb(OH) 2  Stannic Hydroxide  Zinc Hydroxide

Empirical and Molecular Formulas

Empirical Formula  The formula that gives the simplest whole number ration of atoms in a compound  Molecular Formula:C 6 H 12 O 6  Empirical Formula:CH 2 O

What is the empirical formula of…?  C 6 H 12 O 6  Fe 3 O 2  C 6 H 10 O 4  CH 2 O  Fe 3 O 2  C 3 H 5 O 2