Elements and Ionic Compounds Unit II: Intro to Formulas LPChem1415

A. Element OR Compound? Elements:  Formulas only contain ONE symbol  Which means only ONE capital letter.  Names are only ONE word long. Compounds:  Formulas contain two or more symbols.  Which means more than one capital letter.  Names are TWO words long. LPChem1415

Elements: A Review We already learned that:  Most element formulas consist of the element symbol and nothing more.  (Al, Cu, Ne, Au, etc.)  Seven elements are “diatomic” and always pair up in the elemental state:  (H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2 )  Elements go by their own names  But sometimes Carbon is sneaky. LPChem1415

Compounds  There are different types of chemical compound. For this unit, we are only learning IONIC compounds:  Ionic compounds form by transfer of valence electrons. LPChem1415  Valence electrons are the outermost electrons in an atom.  This atom has lots of electrons. But only ONE in its VALENCE.

LPChem1415 The periodic table  The table is organized so similar elements are together.  Similar properties are usually due to similar # of valence electrons.

LPChem1415  Groups of similar elements have special names:

LPChem1415  # valence electrons increases, left to right:

LPChem1415  Sodium has 1 valence electron  Chlorine has 7 valence electrons

Lewis Dot Structures  Show ONLY valence electrons  Each electron is shown as a dot.  Electrons come in pairs– top, bottom, left, & right of symbol. LPChem1415

Valence Electrons & Stability  Eight valence electrons = a “full octet”  Atoms with a full octet are the most stable  This is why the noble gases are “noble”

Valence Electrons & Stability  All other elements work to achieve a “full octet” by gaining, losing, or sharing electrons: LPChem1415 Atoms are like onions– the electrons come in layers. The sodium now has zero electrons in the diagram, but there was already a full octet in the next lower layer, so it is stable now.

Valence Electrons & Stability  Gaining or losing electrons gives the atom a charge.  Charged particles are called IONS.  If one atom loses electrons, another must gain them.  Even tiny electrons are matter, and can’t be created or destroyed! LPChem1415

Valence Electrons & Stability  An atom that loses electrons becomes positively charged.  This is a cation. LPChem1415 (Subtracting a negative makes a positive!)

Cations are Positive LPChem1415

Valence Electrons & Stability  An atom that gains electrons becomes negatively charged.  This is an anion. LPChem1415 Note: the name changes to the “–ide” form when it becomes negative!

LPChem1415  Barium is in column 2 and has 2 valence electrons  Sulfur is in column 16 and has 6 valence electrons

LPChem1415  To get full octets:  Barium must lose TWO electrons  Sulfur must gain TWO electrons  Key Point: Ion charge is based on how many electrons must be gained or lost to get a full octet.

Valence Electrons & Stability Main Group Ion Charges LPChem ±4±

 Form because opposite charged ions attract each other. Ionic Compounds LPChem14  Cations and anions arrange themselves in a “crystal lattice.”

Ionic Crystals  A “crystal lattice”  Is a 3-D grid of ions– the general structure of ionic compounds LPChem1415  Is hard to melt due to attraction between anions and cations

C. Ionic Nomenclature Ionic Names: Cations  Write the name of the cation first.  Stock System: Use Roman numerals to show the cation’s charge if more than one is possible.  D-block (transition metals)  Poor metals LPChem1415

C. Ionic Nomenclature  How do you know the Roman numeral? Math! (The overall charge must equal zero.) o FeCl 2 LPChem1415 Cl gets a charge of: 1- (because it is in column 17) Fe must have a charge of ____ to make the compound = 0 2+ o This is Iron (II) Chloride

C. Ionic Nomenclature  Fe 2 S 3  There are only two capital letters, so no polyatomic ion to worry about.  I look up S on the periodic table o Column 16: o 6 valence electrons, 2- charge LPChem1415 S

C. Ionic Nomenclature  Fe 2 S 3 = iron ( ? ) sulfide LPChem1415 Fe 2 S ( ) 3 = 0 6+ ( ) Iron (III) sulfide

C. Ionic Nomenclature  Fe 2 (CO 3 ) 3 = iron ( ? ) carbonate LPChem1415 Fe 2 (CO 3 ) ( ) 3 = 06+ ( ) Iron (III) carbonate

C. Ionic Nomenclature  Fe CO 3 = iron ( ? ) carbonate LPChem1415 Fe CO 3 2- ( ) 1 = 02+ ( ) Iron (II) carbonate

C. Ionic Nomenclature  Ni 2 CO 3 = nickel ( ? ) carbonate LPChem1415 Ni 2 CO 3 2- ( ) 1 = 02+ ( ) Nickel (I) carbonate

C. Ionic Nomenclature Ionic Names: Cations  Roman numerals are NOT needed for:  Group 1 & 2 o (1+, 2+)  Ag, Zn, Al LPChem1415

C. Ionic Nomenclature  Monatomic anion names are the first syllable of the element name, then -ide.  (Chloride, oxide, phosphide, nitride, etc)  Polyatomic ions have special names. (Chart on the back of your periodic table.)  Do NOT change the ending of polyatomic ions. LPChem1415 Ionic Names: Anions

C. Ionic Nomenclature  Consider the following:  Does it contain a polyatomic ion? o 2 elements  no; ending is “-ide” o 3+ elements  yes; ending is -ate -ite  Does it contain a Roman numeral? o Check the table: is the metal NOT in Groups 1 or 2 (or Ag, Zn, Al)?  NO numerical prefixes! LPChem1415 Overview:

C. Ionic Nomenclature LPChem1415  NaBr  Na 2 CO 3  FeCl 3  sodium bromide  sodium carbonate  iron(III) chloride