IONIC COMPOUNDS Chapter 8

Forming Chemical Bonds Section 8.1 The force that holds two atoms together is called a chemical bond. Chemical bonds may form by the attraction between a positive nucleus and negative electrons or the attraction between a positive ion and a negative ion

Review… Valence electrons are the electrons in the outermost energy level. These same electrons are involved in the formation of chemical bonds between two atoms

Electron-Dot Structures Especially useful when illustrating formation of chemical bonds!!

From Chapter 6… Ionization energy refers to how easily an atom loses an electron. Noble gases, having high ionization energies, show a general lack of chemical reactivity The difference in reactivity is directly related to the valence electrons Elements tend to react to acquire the stable electron structure of a noble gas (V.E. 8)

Formation of Positive Ions A positive ion forms when an atom loses one or more valence electrons in order to attain a noble gas configuration Positively charged ion is called a cation

Transition Metals When forming positive ions, transition metals commonly lose their valence electrons, forming 2+ ions. However, it is also possible for d electrons to be lost A useful rule of thumb for these metals is that they form ions with a 2+ or 3+ charge.

Negatively charged ion is called an anion Nonmetals have a great attraction for electrons and from stable outer electron configuration by gaining electrons Negatively charged ion is called an anion

Checkpoint Why do ions form? Describe the formation of positive and negative ions. Predict the change that must occur to achieve noble gas stability Nitrogen Sulfur Barium Lithium

Answers Atoms gain stability by losing or gaining electrons Positive ions form when atoms lose valence electrons Negative ions form when valence electrons are added to an atom Nitrogen- gain 3 electrons (N3-) Sulfur- gain 2 electrons (S2-) Barium- lose 2 electrons (Ba2+) Lithium- lose 1 electron (Li1+)

The Formation and Nature of Ionic Bonds (Section 8.2) The electrostatic force that holds oppositely charged particles together in an ionic compound is referred to as an ionic bond Ionic bonds form between cations (+) and anions (-) Binary compounds contain two different elements Metallic cation Nonmetallic anion Electrons gained = electrons lost OVERALL CHARGE OF THE COMPOUND FORMED MUST BE ZERO!!!

Properties of Ionic Compounds High Melting and boiling points (indicating strong bond strength) Most are crystalline solids at room temperature ions in a regular, geometric pattern (crystal lattice) hard, brittle conduct electricity when molten or dissolved in water (aka electrolyte)

Names and Formulas for Ionic Compounds (Very Important!) Section 8.3 Terms to be familiar with: Formula Unit- the simplest ratio of the ions represented in an ionic compound Monatomic Ion- a one-atom ion (Mg2+ or Br1-) Oxidation Number- the charge of the monatomic ion Polyatomic Ion- ions made up of more than one atom (i.e. Nitrite= NO2-)

Magnesium and chlorine Aluminum and bromide Cesium and nitride Write the correct formula for the ionic compound composed of the following pairs of ions Potassium and iodine Magnesium and chlorine Aluminum and bromide Cesium and nitride

Answers 1. Potassium and iodine K+1 and I-1  KI (1:1 ratio) 2. Magnesium and chlorine Mg+2 and Cl-1  MgCl2 (1:2 ratio) 3. Aluminum and bromide Al+3 and Br-1  AlBr3 (1:3 ratio) 4. Cesium and nitride Cs+1 and N-3  Cs3N (3:1 ratio)

Compounds Containing Polyatomic Ions The charge given to a polyatomic ion applies to the entire group of atoms The polyatomic ion acts as an individual ion NEVER CHANGE THE SUBSCRIPTS WITHIN THE ION If more than one polyatomic ion is needed, place parentheses around the ion and write the appropriate subscript outside the parentheses.

Practice Problems Calcium and Nitrate Aluminum and Hydroxide Barium and Sulfate Sodium and Phosphate Potassium and Sulfate

Naming Ionic Compounds Oxyanion- a polyatomic ion composed of an element, usually a nonmetal, bonded to one or more oxygen atoms An ion with more oxygen atoms is named using the root of the nonmetal plus the suffix –ate (ex. NO3-  nitrate) An ion with fewer oxygen atoms is named using the root of the nonmetal plus the suffix –ite (ex. NO2-  nitrite )

Chlorine’s 4 Oxyanions ClO4-  perchlorate (most oxygen's) ClO3-  chlorate (one less oxygen) ClO2-  chlorite (two fewer oxygen's) ClO-  hypochlorite (three fewer oxygen's)

Naming Ionic Compounds Name the cation (+) first and the anion (-) second. Monatomic cations use the element name. Monatomic anions take their element name plus the suffix –ide.

4. Group 1A and Group 2A metals have only one oxidation number (charge). Transition metals and metals on the right side of the periodic table often have more than one oxidation number. The oxidation number is written as a Roman numeral in parentheses after the name of the cation 5. If the compound contains a polyatomic ion, simply name the ion.

Practice problems NaBr CaCl2 KOH Cu(NO3)2 Ag2CrO4

Cation + Anion NaBr  sodium bromide CaCl2  calcium chloride KOH  potassium hydroxide Cu(NO3)2  copper (II) nitrate Ag2CrO4  silver chromate

Section Review Anion Cation  Oxide Chloride Sulfate Phosphate Potassium Barium Aluminum Ammonium

Answers Anion Cation  Oxide Chloride Sulfate Phosphate Potassium K2O KCl K2SO4 K3PO4 Barium BaO BaCl2 BaSO4 Ba3(PO4)2 Aluminum Al2O3 AlCl3 Al2(SO4)3 AlPO4 Ammonium (NH4)2O NH4Cl (NH4)2SO4 (NH4)3PO4

Metallic Bonds and Properties of Metals (Section 8.4) Although metals do not bond ionically, they often form lattices in the solid state. Electron sea model- all the metal atoms in a metallic solid contribute their valence electrons to form a “sea” of electrons

The electrons present in the outer energy levels of the bonding metallic ions are not held by any specific atom and can move easily from one atom to the next. (Delocalized electrons) A metallic bond is the attraction of a metallic cation for delocalized electrons

Metal Alloys A mixture of elements that has metallic properties Substitutional- atoms of the original metallic solid are replaced by other metal atoms of similar size Brass, pewter, 10-carat gold, and sterling silver Interstitial- formed when small holes in a metallic crystal are filled with smaller atoms Carbon steel Great test question…