1. Ionic and Metallic Bonding Chapter 7

2. Valence Electrons  Valence electrons are the electrons in the highest occupied energy level of an element’s atoms.  The number of valence electrons largely determines the chemical properties of an element  Number of valence electrons of a main (A) group atom = Group number

3. Determining the Number of Valence Electrons As a general rule, only the valence electrons are shown in electron dot structures. Electron dot structures are diagrams that show valence electrons in the atoms of an element as dots. Valence electrons are usually the only electrons involved in chemical bonds.

4. Lewis (Electron) Dot Structures  Diagrams that show the valence e - Li Mg B Si N S F Ne

5. The Octet Rule  Atoms want to be stable Which group of elements is the most stable? Group 18 – Noble Gases  Octet Rule – atoms seek to achieve the e - configurations of noble gases 8e - in the outermost energy level How can atoms achieve the octet? By gaining or loosing e-

6. Draw the electron dot structure for bismuth, and Carbon.

7. Formation of Cations  A positively charged ion, or cation, is produced when an atom loses one or more valence electrons A sodium atom (Na) forms a sodium cation (Na + ). A calcium atom (Ca) forms a calcium cation (Ca + ). Na 1s 2 2s 2 2p 6 3s 1 Na + 1s 2 2s 2 2p 6 –e – octet Mg Mg 2+ + 2e – loses all its valence electrons Magnesium atom (electrically neutral, charge = 0) Magnesium ion (2+ indicates two units of positive charge) (2 in front of e – indicates two units of negative charge)

8.  How many valence electrons would Al loose to form cation.  Write the symbol with the charge  Write the electron configuration.

9.  Transition Metal Cations : The charges of cations of the transition metals may vary.  An atom of iron may lose two valence electrons, forming the Fe 2+ cation, or three valence electrons, forming the Fe 3+ cation Formation of Cations

10. Silver, with the electron configuration of 1s 2 2s 2 2p 6 3s 2 2p 6 3d 10 4s 2 4p 6 4d 10 5s 1, is an example. To achieve the structure of krypton, a silver atom would have to lose eleven electrons. To acquire the electron configuration of xenon, a silver atom would have to gain seven electrons. Ions with charges of three or greater are uncommon. Some ions formed by transition metals do not have noble-gas electron configurations (ns 2 np 6 ) and are therefore exceptions to the octet rule. Transition Metal Cations

11.  How does a cesium atom form a cation? A.By losing 2 electrons B.By gaining 1 electron C.By losing 1 electron D.By gaining 2 electrons

12.  How does a cesium atom form a cation? A.By losing 2 electrons B.By gaining 1 electron C.By losing 1 electron D.By gaining 2 electrons

13.  An anion is produced when an atom gains one or more valence electrons.  Atoms of nonmetals and metalloids form anions by gaining enough valence electrons to attain the electron configuration of the nearest noble gas  The name of the anion typically ends in -ide.  Thus, a chlorine atom (Cl) forms a chloride anion (Cl – ).  An oxygen atom (O) forms an oxide anion (O 2– ). Formation of Anions

14.  This table lists some common anions. Some Common Anions NameSymbolCharge Fluoride F–F– 1–1– ChlorideCl – 1–1– BromideBr – 1–1– IodideI–I– 1–1– OxideO2–O2– 2–2– SulfideS2–S2– 2–2– NitrideN3–N3– 3–3– PhosphideP3–P3– 3–3–

15.  What is the electron configuration of a sulfide ion? What noble gas shares this configuration? S 2– : 1s 2 2s 2 2p 6 3s 2 3p 6 This is the same configuration as Ar.

16.  An ionic compound is a compound composed of cations and anions.  Cations are the metals and anions are the nonmetals.  Ionic compound is electrically neutral and electrons are transferred from one metal to nonmetal.  Electrostatic forces hold the compound together (ionic bond). Formation of Ionic Compounds

17.  A chemical formula shows the numbers of atoms of each element in the smallest representative unit of a substance  NaCl is the chemical formula for sodium chloride.  MgCl 2 is the chemical formula for magnesium chloride.  Formula Units : Ionic compounds do not exist as discrete units, but as collections of positively and negatively charged ions arranged in repeating patterns. A formula unit is the lowest whole-number ratio of ions in an ionic compound. Formation of Ionic Compounds

18. Formula Units For sodium chloride, the lowest whole-number ratio of the ions is 1:1 (one Na + ion to each Cl – ion). The formula unit for sodium chloride is NaCl. Although ionic charges are used to derive the correct formula, they are not shown when you write the formula unit of the compound.

19.  Predict the formulas of the ionic compounds formed from the following elements: Predicting Formulas of Ionic Compounds a.potassium and oxygen b.magnesium and nitrogen

20.  Most ionic compounds are crystalline solids at room temperature  Ionic compounds generally have high melting points.  Ionic compounds can conduct an electric current when melted or dissolved in water. Properties of Ionic compounds

21.  When can ionic compounds conduct an electric current? A. Only when melted B.When melted or dissolved in water C.Only when dissolved in water D.When solid or melted

22.  When can ionic compounds conduct an electric current? A. Only when melted B.When melted or dissolved in water C.Only when dissolved in water D.When solid or melted

23.  Metals consist of closely packed cations and loosely held valence electrons (sea of electrons) rather than neutral atoms.  Metallic bonds are the forces of attraction between the free-floating valence electrons and the positively charged metal ions. Bonding in Metals

24.  Free floating valence e - explain metallic properties: Good conductors Malleable & Ductile Luster Bonding in Metals

25.  How are metals and ionic compounds different? How are they similar? Both metals and ionic compounds form crystal structures. However, they have different configurations of electrons. The sea of electrons surrounding cations in a metal allows metals to be ductile and malleable. Ionic crystals will fracture under pressure.

26.  Metal atoms are arranged in very compact & orderly patterns Crystalline Structure of Metals

27. Coordination Number  The coordination number of an ion is the number of ions of opposite charge that surround the ion in a crystal. In NaCl, each ion has a coordination number of 6. In CsCl, each ion has a coordination number of 8. The coordination number for the cation (Ti 4+ ) is 6. The coordination number of the anion (O 2– ) is 3.

28.  Alloys are mixtures of two or more elements, at least one of which is a metal.  Brass, for example, is an alloy of copper and zinc.  Alloys are important because their properties are often superior to those of their component elements  Sterling silver is 92.5 percent silver and 7.5 percent copper. Alloys Stainless Steel 80.6% Fe 18.0% Cr 0.4% C 1.0% Ni

29.  Explain why alloys are important, and list one important alloy. Alloys are important because they often have properties that are superior to those of the elements from which they are made. Stainless steel is an important alloy because of its corrosion resistance.