2Forming 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
3Review…Valence electrons are the electrons in the outermost energy level. These same electrons are involved in the formation of chemical bonds between two atoms
4Electron-Dot Structures Especially useful when illustrating formation of chemical bonds!!
5From 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 reactivityThe difference in reactivity is directly related to the valence electronsElements tend to react to acquire the stable electron structure of a noble gas (V.E. 8)
6Formation of Positive Ions A positive ion forms when an atom loses one or more valence electrons in order to attain a noble gas configurationPositively charged ion is called a cation
7Transition MetalsWhen forming positive ions, transition metals commonly lose their valence electrons, forming 2+ ions.However, it is also possible for d electrons to be lostA useful rule of thumb for these metals is that they form ions with a 2+ or 3+ charge.
8Negatively charged ion is called an anion Nonmetals have a great attraction for electrons and from stable outer electron configuration by gaining electronsNegatively charged ion is called an anion
9Checkpoint Why do ions form? Describe the formation of positive and negative ions.Predict the change that must occur to achieve noble gas stabilityNitrogenSulfurBariumLithium
10Answers Atoms gain stability by losing or gaining electrons Positive ions form when atoms lose valence electronsNegative ions form when valence electrons are added to an atomNitrogen- gain 3 electrons (N3-)Sulfur- gain 2 electrons (S2-)Barium- lose 2 electrons (Ba2+)Lithium- lose 1 electron (Li1+)
11The 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 bondIonic bonds form between cations (+) and anions (-)Binary compounds contain two different elementsMetallic cationNonmetallic anionElectrons gained = electrons lostOVERALL CHARGE OF THE COMPOUND FORMED MUST BE ZERO!!!
12Properties of Ionic Compounds High Melting and boiling points (indicating strong bond strength)Most are crystalline solids at room temperatureions in a regular, geometric pattern (crystal lattice)hard, brittleconduct electricity when molten or dissolved in water (aka electrolyte)
13Names 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 compoundMonatomic Ion- a one-atom ion (Mg2+ or Br1-)Oxidation Number- the charge of the monatomic ionPolyatomic Ion- ions made up of more than one atom (i.e. Nitrite= NO2-)
14Magnesium and chlorine Aluminum and bromide Cesium and nitride Write the correct formula for the ionic compound composed of the following pairs of ionsPotassium and iodineMagnesium and chlorineAluminum and bromideCesium and nitride
15Answers 1. Potassium and iodine K+1 and I-1 KI (1:1 ratio) 2. Magnesium and chlorineMg+2 and Cl-1 MgCl2 (1:2 ratio)3. Aluminum and bromideAl+3 and Br-1 AlBr3 (1:3 ratio)4. Cesium and nitrideCs+1 and N-3 Cs3N (3:1 ratio)
16Compounds Containing Polyatomic Ions The charge given to a polyatomic ion applies to the entire group of atomsThe polyatomic ion acts as an individual ionNEVER CHANGE THE SUBSCRIPTS WITHIN THE IONIf more than one polyatomic ion is needed, place parentheses around the ion and write the appropriate subscript outside the parentheses.
17Practice Problems Calcium and Nitrate Aluminum and Hydroxide Barium and SulfateSodium and PhosphatePotassium and Sulfate
20Naming Ionic Compounds Oxyanion- a polyatomic ion composed of an element, usually a nonmetal, bonded to one or more oxygen atomsAn 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 )
22Naming 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.
234. 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 cation5. If the compound contains a polyatomic ion, simply name the ion.
28Metallic 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
29The 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
30Metal Alloys A mixture of elements that has metallic properties Substitutional- atoms of the original metallic solid are replaced by other metal atoms of similar sizeBrass, pewter, 10-carat gold, and sterling silverInterstitial- formed when small holes in a metallic crystal are filled with smaller atomsCarbon steelGreat test question…