Unit 6 Ionic Compounds

Remember…  The electrons in the outermost level or shell are called… –Valence electrons  You can determine the number of valence electrons in the s & p blocks by looking at the… –Group number

Remember…  Atoms in the same column have the same properties because they have the same… –Outer electron configuration –Number of valence electrons

Remember…  Lewis Dot Diagrams  A way of keeping track of valence electrons –Write the symbol –Put one dot for each valence electron –Don’t pair up until they have to X

Lewis Dot diagram for Nitrogen  Nitrogen has 5 valence electrons.  First we write the symbol N  Then add 1 electron at a time to each side  Until they are forced to pair up

Stable Electron Configurations  Atoms want to be stable!  Stable = noble gas configuration –8 valence electrons (s 2 & p 6 )  So…atoms will form ions to achieve that stable electron configuration

Atoms and ions  Atoms are electrically neutral –Same # of protons and electrons  Ions are atoms, or groups of atoms, with a charge –Different # of protons and electrons  Only electrons can be added or removed  So to become an ion, atoms gain or lose electrons

Remember…  Elements differ by the number of protons  Isotopes differ by the number of neutrons  Ions differ by the number of electrons

Forming Ions  Some atoms LOSE electron(s) to achieve a noble gas configuration  More protons than electrons so it becomes a positively charged ion  + charged ion = Cation  Occurs in metals

Examples of Cations  Na – 11 electrons - 1s 2 2s 2 2p 6 3s 1 –1 valence electron – VERY reactive  Na electrons - 1s 2 2s 2 2p 6 –Noble gas configuration - STABLE K 1+ Has lost one electron Ca 2+ Has lost two electrons

Electron Dots For Cations  Metals have few valence electrons  They lose these electrons to become stable Ca

Electron Dots For Cations  Metals have few valence electrons  These will come off Ca

Electron Dots For Cations  Metals have few valence electrons  These will come off  Forming a positive ion (cation) Ca 2+

Forming Ions  Some atoms GAIN electron(s) to achieve a noble gas configuration  More electrons than protons so it becomes a negatively charged ion  Negatively charged ion = Anion  A Negative ION  Occurs in nonmetals

Examples of Anions  S – 16 electrons - 1s 2 2s 2 2p 6 3s 2 3p 4 –6 valence electrons = REACTIVE  S electrons - 1s 2 2s 2 2p 6 3s 2 3p 6 –Noble gas configuration = STABLE F 1- Has gained one electron O 2- Has gained two electrons

Electron Dots For Anions  Nonmetals have several valence electrons  They will gain electrons to fill outer shell. P P 3-

Practice  Use electron dot diagrams to show how the following form ions  Al  Cl KK OO

Atomic Number # of protons # of electrons Cl Cl - K K +

Transition metals  WEIRD!  Form cations  Hard to predict the charge  Often will form more than 1 charge  Can’t form noble gas configuration b/c it would take too much energy  Still try to fill up orbitals

Examples  Zinc –1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2  Zn 2+ –1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 –Full 3 rd energy level  Fe 1s 2 2s 2 2p 6 3s 2 3p 6 3d 6 4s 2  Fe 2+ 1s 2 2s 2 2p 6 3s 2 3p 6 3d 5 4s 1  Fe 3+ 1s 2 2s 2 2p 6 3s 2 3p 6 3d 5

Naming ions  Cations keep the name of the metal –Ca calcium –Ca 2+ calcium ion  Anions change ending to –ide –Cl chlorine –Cl 1- chloride ion

Polyatomic ions  Groups of atoms that stick together as a unit, and have a charge  Names often end in –ate or –ite  You need to memorize the following 6: –PO 4 3- phosphate –CO 3 2- carbonate –SO 4 2- sulfate –NO 3 - nitrate –OH - - hydroxide –NH ammonium

Stable Electron Configurations  Atoms want to be stable!  Stable = noble gas configuration –8 valence electrons (s 2 & p 6 )  Also called the octet rule –In forming compounds, atoms try to obtain 8 electrons in the highest energy level

Achieving Stability  Forming ions  Bonding with other ions to form an ionic compound

Ionic Bonding  Anions and cations join together to form ionic compounds (AKA salts)  The bond is formed through the transfer of electrons  Electrons are transferred to achieve noble gas configuration

Ionic Bonding NaCl 1+ 1-

Ionic Compounds (Salts)  Made up of –a positive and negative ion –a cation and an anion –a metal and a nonmetal (or polyatomic ion)  Simplest ratio of elements = formula unit

Properties of Ionic Compounds  Crystalline structure –A regular repeating arrangement of ions in the solid –Repeating unit is called unit cell –Structure is rigid –Ions are strongly bonded

Crystalline structure

Cubic

Body-Centered Cubic

Properties of Ionic Compounds  High melting points- because of strong forces between ions  Good conductors of electricity when dissolved in water or melted

Ionic Bonding  All the electrons must be accounted for! CaP

Ionic Bonding CaP

Ionic Bonding Ca 2+ P

Ionic Bonding Ca +2 P Ca

Ionic Bonding Ca 2+ P 3- Ca

Ionic Bonding Ca 2+ P 3- Ca P

Ionic Bonding Ca 2+ P 3- Ca 2+ P

Ionic Bonding Ca 2+ P 3- Ca 2+ P Ca

Ionic Bonding Ca 2+ P 3- Ca 2+ P Ca

Ionic Bonding Ca 2+ P 3- Ca 2+ P 3- Ca 2+

Ionic Bonding Ca 3 P 2 Formula Unit

Practice  Use electron dot diagrams to show how the following elements make an ionic compound and write the formula unit  Mg and Cl

Practice  Na and N

Practice  Al and O

Writing formulas  Ionic compounds have no overall charge  So we add the correct subscripts to represent the # of atoms that balance the ions  Na + Cl - = 1:1 = NaCl  Zn 2+ S 2-

Writing formulas  Na 1+ O 2- –Need 2 Na 1+ to balance the O 2- –Na 2 O  Sr 2+ Cl 1-

Writing Formulas – Criss-Cross 1. Write the ions side by side. Fe 3+ S 2-

Writing Formulas – Criss-Cross 2. Draw arrows that cross each other. Fe 3+ S 2-

Writing Formulas – Criss-Cross 3. Put the number of charges at the ends of the arrows. Fe 3+ S 2- 23

Writing Formulas – Criss-Cross 4. Write the formula by using the numbers at the ends of the arrows as subscripts Fe 3+ S Fe 2 S 3

Using Polyatomic Ions  Same rules but put a bracket around the entire ion before adding the subscript  Na + OH - = 1:1 = NaOH  Mg 2+ OH - = 2:1 = Mg[OH] 2  Na + CO 3 2- = 1:2 = Na 2 CO 3  Cu 2+ PO 4 3- = 2:3 = Cu 3 [PO 4 ] 2

Naming Ionic Compounds  First name the cation then the anion  Cation –Usually the same name as the metal –If a transition metal, name the metal and use a roman numeral for the charge of the ion. Example, Fe 2+ or Fe 3+, iron (II) and iron (III) ions

Naming Ionic Compounds  Anion –Ends with –ide  If a polyatomic ion is in the compound, don’t change the name, just name it.

Examples  NaCl –Cation = Na (sodium) –Anion = Cl (chlorine) ide Sodium Chloride

 MgBr –Cation = Mg (magnesium) –Anion = Br (bromine) ide Magnesium bromide

 NaOH –Cation = Na (sodium) –Anion = OH (hydroxide) Sodium hydroxide  MgSO 4  Cation = Mg (magnesium)  Anion = SO 4 (sulfate) Magnesium sulfate

 FeCl 2 –Cation = Fe (Iron) –Anion = Cl (chlorine) ide  Which iron is this?  Cl has a -1 charge and there are 2 so the total negative charge is -2  That means there must be a positive charge of +2 for the iron Iron (II) chloride

Name  Formula 1.Start by writing the symbols of each element. 2.Then add the charges of each ion. 3.Use subscripts to balance the charges.

Name  Formula  Sodium sulfide  Na S   Na 2 S

Ionic Bonding  Ionic bonds form between… –Metals & Nonmetals  But it is possible for nonmetals to bond to each other –Covalent bond  And for metals to bond to each other –Alloy

Alloys SSolutions made by dissolving metal into other elements (usually metals) MMade by melting them together and cooling them IIf the atoms of the metals are about the same size, they substitute for each other CCalled a substitutional alloy

Metal A Metal B +  Substitutional alloy Bronze – Copper and Tin Brass- 60 % Copper 39% Zinc and 1%Tin 18 carat gold- 75% gold, 25%Ag or Cu

Alloys  If the atoms of the metals are different sizes, the small one will fit into the spaces of the larger one  Called an interstitial alloy

Metal A +  Metal B Interstitial Alloy Steel – 99% iron 1 % C Cast iron- 96% Iron, 4%C

Alloys  Making an alloy is still just a mixture  Blend the properties  Designed for a purpose

For Your Quiz  Valence electrons  Elements vs Isotopes vs Ions  Cation vs Anion  Naming Ions  KNOW YOUR POLYATOMIC IONS  Characteristic Properties of Salts  Ionic bond forms between….  Naming compounds/ writing formulas  Alloys