2Forming Chemical Bonds The atoms in compounds are held together by a force called a chemical bond.These bonds form because of an attraction between oppositely charged atoms, ions, or between electrons and the nuclei.The valence electrons are the ones mainly involved in bonding.Remember that elements in the same group have the same number of valence electrons.
3IonsElements react so that they can achieve the stable electron configuration of a noble gas, usually an octet of electrons.Remember, a cation is a positive ion formed when electrons are lost.Anions are negative ions formed when electrons are gained.The periodic table can be used to predict charges.
4PracticeFor each of the following atoms, write the e- configuration. Then write the formula of the ion most likely to form and identify as a cation or anion. Finally, write the e- configuration of the ion.Bromine, element 35Gallium, element 31Sulfur, element 16Rubidium, element 37
5Formation and Nature of Ionic Bonds To bond ionically, atoms must transfer valence e-.An atom that loses one or more e-, becomes a positive ion.An atom the gains one or more e-, becomes a negative ion.An ionic bond is an electrostatic force holding oppositely charged ions together.
6ProblemsWrite the e- configuration, in abbreviated form for the atoms in each pair. Then determine the ratio of the atoms in the ionic compound formed in each case.Aluminum and fluorineLithium and oxygenBeryllium and seleniumGallium and sulfur
7Properties of Ionic Compounds Ionic compounds are always nonconductors of electricity when solid, but good conductors when melted.They also act as electrolytes, substances that conduct electric current when dissolved in water.These characteristics are ways that ionic compounds can be identified, although each one individually is not reliable.
8Lattice EnergyIn a solid ionic compound, the positive ions are surrounded by negative ions and the negative ions by positive ions.The resulting structure is called a crystal lattice and contains a regular, repeating 3-D arrangement of ion.This arrangement involves strong attraction between oppositely charged ions, and produces certain properties, such as mp, bp and brittleness.
9Lattice EnergyThe amount of energy required to separate one mole of ions of an ionic compound is called the lattice energy.This value is expressed as a negative number.The more negative the number, the stronger the force of attraction between the ions.Lattice energy is greater for more highly charged ions and small for ions of lower charge or size.
10ProblemOn the basis of the properties of the following “unknowns”, classify each as either ionic or not ionic.Conducts electricity when solidConducts electricity when liquid and has a low mpHas a high bp and shatters when hammeredHigh mp and conducts electricity when dissolved in water
11ProblemFor each of the following pairs of ionic compounds, state which would be expected to have the higher (more negative) lattice energy.a. LiF or KBrb. NaCl or MgSc. MgO or RbI
12Names and Formulas for Ionic Compounds Section 8.3
13Why Formal NamesRemember that scientists come from all over the world.The chemicals they referr to in conversation must be easily understood.Therefore a set of rules is used in the naming of compounds.This allows everyone to write a chemical formula when given the name and the name the compound when given the formula.
14Formulas for Ionic Compounds Remember that ionic compounds form crystal structures by the way the ions arrange in the 3-D structure.The smallest ratio of the ions represented in an ionic compound is called the formula unit.Because the total # of e- gained by nonmetals is equal to the # lost by metals, the overall charge of a formula unit is zero.
15Determining ChargeBinary ionic compounds are composed of a positively charged monatomic ions and negatively charged monatomic ions of a nonmetal.A monatomic ion is a one-atom ion, such as Mg2+The charge of a monatomic ion is its oxidation number.
16Oxidation NumbersTransition metals are named that because many of them can have more than one oxidation number.The oxidation state of an element in an ionic compound is the number of e- transferred from an element to form the ion.The oxidation # is used to determine the formulas of the ionic compounds they form.
17Writing FormulasWhen writing the formula of a compound remember that the oppositely charged ions must have a sum of zero.When writing formulas, the cation symbol comes first, followed by the anion symbol.Subscripts are used to represent the number of ions of each element in an ionic compound. If no subscript, it is assumed to be one.
18ExampleLet’s write the correct formula for the ionic compounds composed of the following elements.Potassium and iodineMagnesium and chlorineAluminum and bromineCesium and nitrogenBarium and sulfur
19Polyatomic Ions Some ionic compounds contain polyatomic ions. Polyatomic ions are ions made up of more than one atom.The charge given to a polyatomic ion applies to the entire group of atoms.Since polyatomic ions exist as a unit, do not change the subscripts of the atoms in the ions. Instead use parentheses.
20Common Polyatomic Ions Learn the list of polyatomic ions and their charges as listed on page 224 in table 8-6.
21Naming Ions and Ionic Compounds Most polyatomic ions are oxyanions.An oxyanion is a polyatomic ion composed of an element bonded to one or more oxygen atoms.Rules.The ion with more oxygen atoms is named using the root of the nonmetal plus the suffix –ate.The ion with fewer oxygen atoms is named using the root of the nonmetal plus the suffix –ite.For example:NO NO SO SO32-
22Other Oxyanions Some elements form more than two oxyanions. These are named according to the number of oxygen atoms present.Examples,ClO ClO ClO ClO-
23Rules for Naming Oxyanions The rules for naming oxyanions are as follows:The oxyanion with the greatest number of oxygen atoms is named using the prefix per-, the root of the nonmetal and the suffix –ate.The oxyanion with one less oxygen atom is named with the root of the nonmetal and the suffix –ate.The oxyanion with two fewer oxygen atoms is named using the root of the nonmetal plus the suffix –ite.The oxyanion with three fewer oxygen atoms is name using the prefix hypo-, the root of the nonmetal, and the suffix –ite.
24Naming Ionic Compounds Name the cation first and the anion second.Monatomic cations use the element name.Monatomic anions take their name from the root of the element name plus the suffix –ide.If an element has more than one oxidation number, the oxidation # of the element in that compound must be indicated with a Roman numeral in parentheses following the cation.If the compound contains a polyatomic ion, simply name the ion.
25ExamplesName the following compounds.NaBrCaCl2KOHCu(NO3)2Ag2CrO4
26Metallic Bonds and Properties of Metals Section 8.4
27Metallic BondsAlthough they are not ionic, they share several properties.Metallic bonds form lattices in the solid state.In these lattices, the valence e- of the metals overlap, to create the electron sea model.The e- are not held by any specific atom but rather move easily from one atom to the next.They are often called delocalized electrons.
28Metallic BondsThe moving of the electrons causes the formation of the metallic cation.Each cation is bonded to the next and they are surrounded in a sea of e-.A metallic bond is the attraction of a metallic cation for delocalized electrons.
29Properties of MetalsThe properties of metals can be explained by metallic bonding.Melting/Boiling points–In general, moderately high melting and boiling pointsMaleability–They can be hammered into sheetsDuctileThey can be drawn into wire
30Properties (cont’d) Durability– Conductivity— Hardness/Strength— The cations are not removed from the metal easily.Conductivity—Sea of electrons allows them to conduct electricity.Hardness/Strength—Increased with an increase in the # of delocalized e-
31Alloys An alloy is a mixture of elements that has metallic properties. Alloys most commonly form when elements have similar size or one is significantly smaller than the other.Two basic types, substitutional and interstitial.
32Examples of Alloys Examples of alloys are: Brass Bronze Cast Iron Gold, 10 caratPewterStainless steelSterling silver