Ionic Compounds and Metals Chemistry Unit 6

Main Ideas Ions are formed when atoms gain or lose valence electrons to achieve a stable octet electron configuration. Oppositely charged ion attract each other, forming electrically neutral ionic compounds. In written names and formulas for ionic compounds, the cation appears first, followed by the anion. Metals form crystal lattices and can be modeled as cations surrounded by a “sea’” of freely moving valence electrons.

Ion Formation Ions are formed when atoms gain or lose valence electrons to achieve a stable octet electron configuration. Goals and Objectives: Define a chemical bond. Describe the formation of positive and negative ions. Relate ion formation to electron configuration.

Valence Electrons and Chemical Bonds Chemical Bond – is a force that holds two atoms together. They can form between the positive nucleus of one atom and the negative valence electrons of another atom or between two oppositely charged ions.

Valence Electrons and Chemical Bonds Atom’s try to form the octet – the stable arrangement of eight valence electrons in the outer energy level – by gaining or losing valence electrons. The transfer of valence electrons between two atoms is based on the ionization energy and electron affinity of the two atoms. Noble gases- high ionization energy + low electron affinity = little chemical reactivity.

Positive Ion Formation Cation – positively charged ion Example: Sodium atom: 1s 2 2s 2 p 6 3s 1 Sodium ion: 1s 2 2s 2 p 6 = neon

Positive Ion Formation Metal atoms are reactive because they lose valence electrons easily. Group 1: commonly form +1 ions Group 2: commonly form +2 ions Group 13: sometimes +3 ions

Positive Ion Formation Transition metal ions have an outer shell of s 2 They will lose their s electrons and occasionally a d electron. Typically form +2 or +3 ions but can form greater than +3 ions

Positive Ion Formation Other relatively stable electron arrangements are referred to as pseudo-noble gas configurations. Groups will lose electrons to form full outer shells: s, p, and d.

Negative Ion Formation An anion is a negatively charged ion. (Add “-ide” to the end of the root atom name.) Nonmetals easily gain electrons. Example: Chlorine atom: 1s 2 2s 2 p 6 3s 2 p 5 Chlorine ion: 1s 2 2s 2 p 6 3s 2 p 6 = Argon

Negative Ion Formation Nonmetal ions gain the number of electrons required to fill an octet. Some nonmetals can gain or lose electrons to complete an octet. Phosphorus can gain 3 or lose 5 Group 15 usually gains 3 electrons Group 16 usually gains 2 electrons Group 17 usually gains 1 electron

Practice Problems CALM 6:1

Ionic Bonds and Ionic Compounds

Oppositely charged ions attract each other, forming electrically neutral ionic compounds. Goals and Objectives: Describe the formation of ionic bonds and the structure of ionic compounds. Generalize about the strength of ionic bonds based on the physical properties of ionic compounds. Generalize about the strength of ionic bonds based on the physical properties of ionic compounds. Categorize ionic bond formation as exothermic or endothermic. Categorize ionic bond formation as exothermic or endothermic.

Ionic Bond Ionic Bond is the electrostatic force that holds oppositely charged particles together. Ionic Compound is a compound that contains an ionic bond. Ionic bonds between metals and oxygen are called oxides. Most other ionic compounds are considered salts.

Binary Ionic Compound Binary Ionic compound is an ionic compound that contains two different elements. One metallic cation and a nonmetallic anion. Examples: NaCl, MgO, KBr, LiF

Ionic Bond Formation Electrons gained and lost in each element must be equal. (conservation of electrons) Calcium and Fluorine Aluminum and Oxygen Sodium and Chlorine

Properties of Ionic Compounds Compounds are organized such that a pattern repeats to balance attraction and repulsion Total charge of a compound is neutral Often highly organized Example: NaCl crystal

Crystal Lattice A crystal lattice is a three dimensional geometric arrangement of particles. Each negative ion is surrounded by a positive ion which results in strong attractions between ions. Size and shape are dependent on relative numbers of ions.

Crystal Lattice Physical Properties: Characteristics of bond strength – ionic bonds are relatively strong and take a large amount of energy to break. Melting point – high Boiling point – high Hardness of material is high: rigid and brittle solids.

Properties of Ionic Compounds

Crystal Lattice Characteristics of the compound: Conducts electricity, conditionally Ions in solid state ionic compounds are locked in place and they do not have free electrons in order to conduct electricity. Ionic compounds that are melted or dissolved in aqueous solutions have ions that are free to move and therefore do conduct electricity Electrolyte – an ionic compound that conducts electricity in an aqueous solution.

Energy and the Ionic Bond Formation of ionic compounds forms a more stable system and therefore reduces the energy required to sustain it. Since the creating of bonds lowers energy, energy is released in the process. The creation of bonds is said to be Exothermic. Exothermic – energy is released during a chemical reaction.

Energy and the Ionic Bond Breaking of ionic compounds reduces the stability of a system and therefore increases the energy required to sustain it. Since the creating of bonds lowers energy, the breaking of bonds increases energy and therefore it is required for the process. Endothermic – energy is absorbed during a chemical reaction.

Lattice Energy Lattice energy is the energy required to separate 1 mole of the ions of an ionic compound. higher the lattice energy the stronger the bond strength. Directly related to the size of the ions bonded. smaller ions form compounds more closely because attraction increases with decreased distance. Also affected by charge of ions Higher ion charge typically has higher lattice energy.

Lattice Energy

Practice Problems CALM 6:2

Names and Formulas for Ionic Compounds

In written names and formulas for ionic compounds, the cation appears first, followed by the anion. Goals and Objectives: Relate a formula unit of an ionic compound to its composition. Write formulas for ionic compounds and oxyanions. Apply naming conventions to ionic compounds and oxyanions.

Formulas for Ionic Compounds A standardized system for naming compounds was developed for much the same reason as the SI unit system. This serves as a universal naming system for communication among the science community.

Formula Unit A formula unit is the chemical formula for an ionic compound and represents the simplest ratio of ions. MgCl 2 not Mg 4 Cl 8 A monoatomic ion is a one atom ion.

Oxidation number Oxidation number (oxidation state) the charge of a monatomic ion.

Formulas for Ionic Compounds The symbol for the cation is written first with the anion second. Subscripts represent the number of atoms of each element in a compound. The total charge must equal zero in an ionic compound.

Polyatomic Ions Polyatomic ions are made up of more than one atom. Formulas for polyatomic ionic compounds Charge applies to the entire group of atoms. Parentheses are used if more than one polyatomic ion is needed to balance a compound. Do not change subscripts within the ion group Example (NH 4 )O

Polyatomic Ions

Oxyanion An oxyanion is a polyatomic negative ion composed of an element, usually a nonmetal, bonded to one or more oxygen.

Oxyanion Naming Rules

Names for Ions and Ionic Compounds 1.Name the cation followed by the anion. 2.For monatomic cations, use the element name. 3.For monatomic anions, use the root of the element with the suffix –ide.

Names for Ions and Ionic Compounds 4.Multiple oxidation states are represented by a Roman numeral in paranthesis after the cation. a)This applies to transition metals with more than one oxidation state and not the Group 1 and 2 cations. b)Example: FeO is Iron (II) oxide; Fe 2 O 3 Iron (III) oxide. 5.With a polyatomic ion, name the cation followed by the name of the polyatomic ion. a)Example: NaOH is sodium hydroxide.

Problem Solving

Practice Problems CALM 6:3

Metallic Bonds and the Properties of Metals

Metals form crystal lattices and can be modeled as cations surrounded by a “sea” of freely moving valence electrons. Goals and Objectives: Describe a metallic bond. Relate the electron sea model to the physical properties of metals. Define alloys, and categorize them into two basic types.

Metals Metals are not ionic but share several properties with ionic compounds. Metals also form lattices in the solid state, where 8 to 12 other atoms closely surround each metal atom. Within the crowded lattice, the outer energy levels of metal atoms overlap.

Electron Sea Model The electron sea model proposes that all metal atoms in a metallic solid contribute their valence electrons to form a "sea" of electron. electron sea modelelectron sea model The electrons are free to move around and are referred to as delocalized electrons, forming a metallic cation. delocalized electronsdelocalized electrons

Metallic Bonds A metallic bond is the attraction of an metallic cation for delocalized electrons metallic bondmetallic bond

Properties of Metals Boiling points are much more extreme than melting points because of the energy required to separate atoms from the groups of cations and electrons.

Properties of Metals Metals are malleable because they can be hammered into sheets. Metals are ductile because they can be drawn into wires.

Properties of Metals Mobile electrons around cations make metals good conductors of electricity and heat. As the number of delocalized electrons increases, so does hardness and strength.

Metal Alloys An alloy is a mixture of elements that has metallic properties. alloy The properties of alloys differ from the elements they contain.

Metal Alloys

Substitutional alloys are formed when some atoms in the original metallic solid are replaced by other metals of similar atomic structure. Interstitial alloys are formed when small holes in a metallic crystal are filled with smaller atoms.

Practice Problems CALM 6:4

Accumulating Content How does the electron configuration of a neutral element compare to that of its ion configuration?

Accumulating Content How does energy and stability relate to ion formation and bond formation?

Accumulating Content What are some physical and chemical properties of metals that are caused by the way they ionize or bond?

Study Guide Key Concepts

A chemical bond is the force that holds two atoms together. Some atoms form ions to gain stability. This stable configuration involves a complete outer energy level, usually consisting of eight valence electrons. Ions are formed by the loss or gain of valence electrons.

Key Concepts The number of protons remains unchanged during ion formation. Ionic compounds contain ionic bonds formed by the attraction of oppositely charged ions. Ions in an ionic compound are arranged in a repeating pattern known as a crystal lattice

Key Concepts Ionic compound properties are related to ionic bond strength. Ionic compounds are electrolytes; they conduct an electric current in the liquid phase and in aqueous solution. Lattice energy is the energy needed to remove 1 mol of ions from its crystal lattice.

Key Concepts A formula unit gives the ratio of cations to anions in the ionic compound. A monatomic ion is formed from one atom. The charge of a monatomic ion is its oxidation number. Roman numerals indicate the oxidation number of cations having multiple possible oxidation states.

Key Concepts Polyatomic ions consist of more than one atom and act as a single unit. To indicate more than one polyatomic ion in a chemical formula, place parentheses around the polyatomic ion and use a subscript. A metallic bond forms when metal cations attract freely moving, delocalized valence electrons.

Key Concepts In the electron sea model, electrons move through the metallic crystal and are not held by any particular atom. The electron sea model explains the physical properties of metallic solids. Metal alloys are formed when a metal is mixed with one or more other elements.

Questions Cations form when atoms _______ electrons. A.gain B.lose C.charge D.delocalize

Questions What is the repeating pattern of atoms in an ionic solid called? A.crystal lattice B.ionic lattice C.energy lattice D.ionic bonding

Questions Give the name of the following: NaClO 4 A.sodium hypochlorite B.sodium chlorite C.sodium chlorate D.sodium perchlorate

Questions As the distance between ions in an ionic bond is shortened, A.the energy to break the bond decreases. B.the electrostatic attraction decreases. C.the electrostatic attraction increases. D.the ionic bond changes to a metallic bond.

Questions An alloy is what type of substance? A.heterogeneous mixture B.compound C.mixture of elements D.element

Questions Which is NOT true about metallic solids? A.Metals are shiny. B.Metals are good conductors of heat and electricity. C.Metals are ductile. D.Metals have relatively low boiling points.

Questions Electrons in an atom’s outer most energy level are referred to as what? A.ions B.cations C.valence electrons D.noble-gas electrons

Questions What is the oxidation state of copper in Cu(II)Cl 2 ? A.1+ B.2+ C.2– D.unable to determine

Questions Which elements naturally occur with a full octet of valence electrons? A.alkali metals B.alkali earth metals C.halogens D.noble gases

Questions How many electrons are in a full octet? A.10 B.8 C.6 D.4

The End