Ions and Ionic Bonds

Review Octet Rule Atoms typically gain or lose valence e- so they will have the same e- configuration as a noble gas. Most noble gases have 8 valence electrons. Helium has only 2 valence electrons.

The Octet Rule 1 valence electron 8 valence electrons Na Ne

The Octet Rule 8 valence electrons 7 valence electrons Cl Ar

The Octet Rule 2 valence electrons He 2 valence electrons Li

Ionic Bonds Ionic bonds are a type of chemical bond based on electrostatic forces between two oppositely-charged ions. It is basically the transfer of one electron from one atom to another

Ionic Bonds An ion is an atom or group of atoms that have a charge. Atoms normally have a neutral charge because most often they have the same number of electrons and protons. They become ions by the loss or addition of one or more electrons. This process is called ionization.

Ionic Bonds An ion that has more electrons than protons is called an anion, and an ion that has fewer electrons than protons is called a cation.

Ionic Bonds The name ion was given by a man named Michael Faraday, which comes from a Greek word meaning “to go” or “a goer”. The word anion comes from the Greek word meaning (a thing) “going up” and cation means (a thing) “going down”.

Ionic Compounds Ionic compound (salt) – compound made of cations and anions. cations are formed from metals anions are formed from non-metals Ionic bond – the force that holds an ionic substance together.

Ionic Bonding Na Cl + -

Ionic bonds Occurs when: 1. a metal atom loses an electron and becomes a positive ion 2. a non-metal atom gains the electron and becomes a negative ion 3. the positive and negative attract each other and form a bond

Ionic Bonding + - IMPORTANT: Although the ions in a salt are charged, the compound as a whole is not.

How do ionic bonds form Use the criss-cross method Step 1- Identify the metal and non-metal Step 2- Write the symbols Step 3- write the charges Step 4- cross over the charges Step 5- remove the charge (+ -) Step 6- simplify the numbers and get rid of 1’s NOTE: THE OVERALL CHARGE ON IONIC FORMULAS SHOULD ALWAYS EQUAL ZERO!!!!!!

Ionic Formulas Chemical formula – indicates the number and type of atoms in a substance. H2O 2 hydrogen atoms + 1 oxygen atom NaNO3 1 sodium ion + 1 nitrogen atom + 3 oxygen atoms Formula unit – lowest whole-number ratio of ions in a compound. The formula unit for table salt is NaCl. 1 unit of Na+ ions per 1 unit of Cl- ions. Formula does not show the charges of the ions.

Ionic Formulas What salt forms when aluminum combines with chlorine? Aluminum has 3 valence electrons. Loses 3 e- to reach octet. Forms Al+3 ion. Chlorine has 7 valence electrions. Gains 1 e- to reach octet. Forms Cl-1 ion. If the compound is neutral, it will take 1 Al+3 ion for every 3 Cl-1 ions. The formula is AlCl3.

Aluminum + Chlorine Cl Cl Al Cl

Ionic Bonds – Writing Formulas CRISS-CROSS METHOD Oxidation numbers (excluding charge) of each ion trade places to become the subscripts in the formula – must be reduced to lowest whole number ratio; 1’s are not written Ca & S Ca2S2 Al & Cl AlCl3 3+ 1- 2+ 2- CaS 18

Writing Ionic Formulas Criss-Cross Method of writing ionic formulas: Criss-cross charges to become subscripts Drop the charges when crossing over. Example: What salt is formed from sodium and sulfur? Na forms +1 ions. S forms -2 ions. Na+1 + S-2  Na2S

Writing Ionic Formulas sodium + chlorine  calcium + bromine  lithium + oxygen  aluminum + oxygen  magnesium + nitrogen  Na+1 + Cl-1  Ca+2 + Br -1  Li+1 + O-2  Al+3 + O-2  Mg+2 + N-3  NaCl CaBr2 Li2O Al2O3 Mg3N2

Writing Ionic Formulas If the subscripts can be reduced, do so. Example: calcium + oxygen Ions: Ca+2 + O-2 Wrong: Ca2O2 Right: CaO Example: lead + oxygen Ions: Pb+4 + O-2 Wrong: Pb2O4 Right: PbO2

Ionic Bonds – Writing Formulas Sodium and chlorine bond in a 1:1 ratio to form NaCl Calcium and chlorine bond in a 1:2 ratio for form CaCl2 What determines each ratio & formula? ________________ oxidation numbers

Ionic Bonds – Writing Formulas Try to predict the ratio and resulting formula for each of the following ions based on their oxidation numbers: Ions Oxidation Numbers Ratio Formula Magnesium & Oxygen Mg2+ & O2- 1:1 MgO Lithium & Sulfur Aluminum & Oxygen Sodium & Phosphorus Barium & Fluorine Li+ & S2- 2:1 Li2S Al3+ & O2- 2:3 Al2O3 Na+ & P3- 3:1 Na3P Ba2+ & F- 1:2 BaF2

We will learn how to write nomenclature for: Ternary Salts 3 or more elements Includes a polyatomic ion Salts with Multiple Oxidation Numbers Can be binary or ternary Includes a transition metal

Polyatomic Ions Polyatomic Ions – ions made of more than one atom. Examples: NO3-1 1 nitrogen atom and 3 oxygen atoms that collectively have a -1 charge. SO4-2 1 sulfur atom and 4 oxygen atoms that collectively have a -2 charge. PO4-3 1 phosphorus atom and 4 oxygen atoms that collectively have a -3 charge. NH4+1 1 nitrogen atom and 4 hydrogen atoms that collectively have a +1 charge.

Polyatomic Ions in Salts Treat them like single-atom ions. But do not change their formula! If you need more than one of a particular polyatomic ion, use parentheses. Example: Na+1 + NO3-1  NaNO3 Mg+2 + NO3-1  Mg(NO3)2 Al+3 + NO3-1  Al(NO3)3

Polyatomic Ions in Salts K+1 + OH-1  Ca+2 + OH-1  Ga+3 + OH-1  NH4+1 + Cl-1  NH4+1 + S-2  NH4+1 + P-3  NH4+1 + SO4-2  KOH Ca(OH)2 Ga(OH)3 NH4Cl (NH4)2S (NH4)3P (NH4)2SO4

Name Formula acetate C2H3O2- or CH3COO- ammonium NH4+ carbonate CO32- chlorate ClO3- chlorite ClO2- chromate CrO42- cyanide CN- dichromate Cr2O72- hydrogen carbonate HCO3- hydroxide OH- hypochlorite ClO- nitrate NO3- nitrite NO2- perchlorate ClO4- permanganate MnO4- phosphate PO43- sulfate SO42- sulfite SO32- Polyatomic Ions Some ions contain more than one element - called a polyatomic ion The group as a whole has an overall charge Examples: Lithium and sulfate would bond together to make Li2SO4 Ammonium and sulfur would bond together to make (NH4)2S

Ternary Salt Naming Contains 3 or more elements: cation & anion – most polyatomic ions are anions, only cation is ammonium (NH4+) Naming: Name the cation (no changes) Name the anion (no changes) Example: Na2SO4 = sodium sulfate Exception: When ammonium is paired with an element anion NH4Cl = ammonium chloride

Al & SO3 Al2(SO3)3 K & PO4 K3PO4 Ternary Salt Formulas + 3- 3+ 2- You must use parentheses if you have more than one polyatomic ion. Be sure to criss-cross the oxidation numbers and write it OUTSIDE of the parentheses. + 3- Al & SO3 Al2(SO3)3 3+ 2- K & PO4 K3PO4 30

Ternary Salt Formulas & Naming Try to predict the formulas and names for each ternary salt: Ions Oxidation Numbers Ratio Formula Name Potassium & Hydroxide K+ & OH- 1:1 KOH potassium hydroxide Calcium & Carbonate Barium & Nitrate Sodium & Phosphate Ammonium & Sulfur Ca2+ & CO32- 1:1 CaCO3 calcium carbonate Ba2+ & NO3- 2:1 Ba(NO3)2 barium nitrate Na3PO4 Na+ & PO43- 1:3 sodium phosphate NH4+ & S2- 1:2 (NH4)2S ammonium sulfide

Salts with Multiple Oxidation #s Naming Transition elements can form more than one type of positive ion. For example, copper can form both Cu+ and Cu2+ ions, and iron can form both Fe2+ and Fe3+ ions. Zinc and silver are two exceptions – they only have one oxidation number The zinc ion is Zn2+ and the silver ion is Ag+.

Salts with Multiple Oxidation #s Naming Transition elements can form more than one type of positive ion. Naming: Name the cation Put the roman numeral representing the oxidation # of the metal in parentheses (do not indicate the charge) Name the anion, changing the ending to “ide” (binary) or naming the polyatomic ion (ternary) Example: FeCl2 = iron (II) chloride FeCl3 = iron (III) chloride

Salts with Multiple Oxidation Numbers Practice Ions Oxidation Numbers Ratio Formula Name Copper & Nitrate Cu+ & NO3- 1:1 CuNO3 copper (I) nitrate Lead & Oxygen Cobalt & Hydroxide Nickel & Phosphate Chromium & Sulfur Pb4+ & O2- 2:1 PbO2 lead (IV) oxide Co3+ & OH- 3:1 Co(OH)3 cobalt (III) hydroxide Ni2+ & PO43- 2:3 Ni3(PO4)2 nickel (II) phosphate Cr2+ & S2- 1:1 CrS chromium (II) sulfide