Topic 6

Chapter 8: Ionic Compounds Formation of Compounds: Basic Concepts Topic 6 Chapter 8: Ionic Compounds Chemical compounds are held together by chemical bonds. Ionic Compounds are formed when electrons from a metal transfer to a nonmetal, and the resulting ions are held together by an attractive electrostatic force. Ionic bonds are one of three types of chemical bonds. The other two are Metallic Bonds (covered later in this chapter), and Covalent (Molecular) bonds, covered in Chapter 9.

The Octet Rule – Why Ionic Bonds Form Formation of Compounds: Basic Concepts Topic 6 The Octet Rule – Why Ionic Bonds Form Noble gases are unlike any other group of elements on the periodic table because of their extreme stability. Each noble gas has eight valence electrons, except for helium, which has two.

This model of chemical stability is called the octet rule. Formation of Compounds: Basic Concepts Topic 6 The Octet Rule The modern model of how atoms react to form compounds is based on the fact that the stability of a noble gas results from the arrangement of its valence electrons. This model of chemical stability is called the octet rule.

Formation of Compounds: Basic Concepts Topic 6 The Octet Rule The octet rule says that atoms can become stable by having eight electrons in their outer energy level, as shown in the noble gas, Neon, (or two electrons in the case of some of the smallest atoms).

Formation of Compounds: Basic Concepts Topic 6 The Octet Rule Elements become stable by achieving the same configuration of valence electrons as one of the noble gases, a noble gas configuration. Click box to view movie clip.

Electrons Can Be Transferred Formation of Compounds: Basic Concepts Topic 6 Electrons Can Be Transferred Sodium is in Group 1, so it has one valence electron. Chlorine is in Group 17 and has seven valence electrons.

Electrons Can Be Transferred Formation of Compounds: Basic Concepts Topic 6 Electrons Can Be Transferred How can the valence electrons of atoms rearrange to give each atom a stable configuration of valence electrons? If the one valence electron of sodium is transferred to the chlorine atom, chlorine becomes stable with an octet of electrons.

Electrons Can Be Transferred Formation of Compounds: Basic Concepts Topic 6 Electrons Can Be Transferred Because the chlorine atom now has an extra electron, it has a negative charge. Also, because sodium lost an electron, it now has an unbalanced proton in the nucleus and therefore has a positive charge.

Electrons Can Be Transferred Formation of Compounds: Basic Concepts Topic 6 Electrons Can Be Transferred Now that each atom has an octet of outer-level electrons, they are no longer neutral atoms; they are charged particles called ions. An ion is an atom or group of combined atoms that has a charge because of the loss or gain of electrons.

Electrons Can Be Transferred Formation of Compounds: Basic Concepts Topic 6 Electrons Can Be Transferred A compound that is composed of ions is called an ionic compound. Note that only the arrangement of electrons has changed. Nothing about the atom’s nucleus has changed. Click box to view movie clip.

Formation of an Ionic Compound Formation of Compounds: Basic Concepts Topic 6 Formation of an Ionic Compound Remember that objects with opposite charges attract each other. The strong attractive force between ions of opposite charge is called an ionic bond. The force of the ionic bond holds ions together in an ionic compound.

Formation of an Ionic Compound Formation of Compounds: Basic Concepts Topic 6 Formation of an Ionic Compound Unprotected aluminum metal reacts with oxygen in air, forming the white coating you can observe on aluminum objects such as lawn furniture. Explain the formation of an ionic compound from the elements aluminum and oxygen.

Formation of an Ionic Compound 1. Analyze the Problem Formation of Compounds: Basic Concepts Topic 6 Formation of an Ionic Compound 1. Analyze the Problem You are given that aluminum and oxygen react to form an ionic compound. Aluminum is a group 3A element with three valence electrons, and oxygen is a group 6A element with six valence electrons. To acquire a noble gas configuration, each aluminum atom must lose three electrons and each oxygen atom must gain two electrons.

Formation of an Ionic Compound Formation of Compounds: Basic Concepts Topic 6 Formation of an Ionic Compound 2. Solve for the Unknown Remember that the number of electrons lost must equal the number of electrons gained. The smallest number evenly divisible by the three electrons lost by aluminum and the two gained by oxygen is six. Three oxygen atoms are needed to gain the six electrons lost by two aluminum atoms.

Formation of an Ionic Compound Formation of Compounds: Basic Concepts Topic 6 Formation of an Ionic Compound 3. Evaluate the Answer The overall charge on one unit of this compound is zero.

Explaining the Properties of Ionic Compounds Formation of Compounds: Basic Concepts Topic 6 Explaining the Properties of Ionic Compounds Ionic compounds are composed of well-organized, tightly bound ions. These ions form a strong, three-dimensional crystal structure. Ionic compounds are crystalline solids at room temperature.

Explaining the Properties of Ionic Compounds Formation of Compounds: Basic Concepts Topic 6 Explaining the Properties of Ionic Compounds Ionic compounds usually have to be heated to high temperatures in order to melt them because the attractions between ions of opposite charge are strong.

Formation of Compounds: Basic Concepts Topic 6 Electrolytes Another physical property of ionic compounds is their tendency to dissolve in water and conduct electricity in the liquid (melted) state. Any compound that conducts electricity when melted or dissolved in water is an electrolyte. In order to conduct electricity, ions must be free to move because they must take on or give up electrons.

Question 1 Answer What is the difference between sodium and chlorine? Basic Assessment Questions Topic 6 Question 1 What is the difference between sodium and chlorine? Answer Sodium is a metal that can be cut with a knife and has a silvery luster where it has been cut. Chlorine is a pale green, poisonous gas that kills living cells.

Basic Assessment Questions Topic 6 Question 2 How many valence electrons must an atom have in its outer energy level in order to be considered stable? Answer The answer is 8.

Basic Assessment Questions Topic 6 Question 3 Do atoms that share a covalent bond have an ionic charge? Answer No, the atoms share electrons and neither atom has a charge.

Forming Chemical Bonds Formation of Compounds: Additional Concepts Topic 6 Forming Chemical Bonds When energy is added to or taken away from a system, one phase can change into another. The force that holds two atoms together is called a chemical bond. Chemical bonds form because of attractions between oppositely charged atoms, called ions, or between electrons and nuclei.

Forming Chemical Bonds Formation of Compounds: Additional Concepts Topic 6 Forming Chemical Bonds A cation, or positive ion, is formed when an atom loses one or more electrons. An anion, or negative ion, is formed when an atom gains one or more electrons.

Determining Charges of Ions Formation of Compounds: Additional Concepts Topic 6 Determining Charges of Ions To determine the electron configuration, refer to the periodic table. Write the formula of the ion the atom is most likely to form. Next, identify that ion as a cation or an anion. Finally, write the electron configuration of the ion.

Determining Charges of Ions Formation of Compounds: Additional Concepts Topic 6 Determining Charges of Ions For example: bromine (Br), element 35 (neutral Br: 1s22s22p63s23p64s23d104p5; ion: Br– , anion 1s22s22p63s23p64s23d104p6)

Properties of ionic compounds and lattice energy Formation of Compounds: Additional Concepts Topic 6 Properties of ionic compounds and lattice energy In 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, three-dimensional arrangement of ions.

Properties of ionic compounds and lattice energy Formation of Compounds: Additional Concepts Topic 6 Properties of ionic compounds and lattice energy The energy required to separate one mole of the ions of an ionic compound is called lattice energy, which is expressed as a negative quantity. The greater (that is, the more negative) the lattice energy is, the stronger is the force of attraction between the ions.

Properties of ionic compounds and lattice energy Formation of Compounds: Additional Concepts Topic 6 Properties of ionic compounds and lattice energy Lattice energy tends to be greater for more-highly-charged ions and for small ions than for ions of lower charge or large size.

Properties of ionic compounds and lattice energy Formation of Compounds: Additional Concepts Topic 6 Properties of ionic compounds and lattice energy Between each of the following pairs of ionic compounds, only one would be expected to have the higher (more negative) lattice energy. 1. LiF or KBr (LiF would have the higher lattice energy) Cinda, this is the way it was typed. The answers to each question are in the parentheses, so I don’t know if they are supposed to be a separate point or not. 2. NaCl or MgS (MgS would have the higher lattice energy)

Names and Formulas for Ionic Compounds Formation of Compounds: Additional Concepts Topic 6 Names and Formulas for Ionic Compounds The simplest ratio of the ions represented in an ionic compound is called a formula unit. The overall charge of any formula unit is zero. In order to write a correct formula unit, one must know the charge of each ion.

Names and Formulas for Ionic Compounds Formation of Compounds: Additional Concepts Topic 6 Names and Formulas for Ionic Compounds The charges of monatomic ions, or ions containing only one atom, can often be determined by referring to the periodic table or table of common ions based on group number.

Names and Formulas for Ionic Compounds Formation of Compounds: Additional Concepts Topic 6 Names and Formulas for Ionic Compounds For example, ions of group 1A typically have a charge of 1+. Those of group 2A have a charge of 2+. Those of group 7A have a charge of 1–.

Names and Formulas for Ionic Compounds Formation of Compounds: Additional Concepts Topic 6 Names and Formulas for Ionic Compounds The charge of a monatomic ion is equal to its oxidation number. The oxidation number, or oxidation state, of an ion in an ionic compound is numerically equal to the number of electrons that were transferred to or from an atom of the element in forming the compound.

Formation of Compounds: Additional Concepts Topic 6 Oxidation Numbers Oxidation numbers can be used to determine the chemical formulas for ionic compounds. If the oxidation number of each ion is multiplied by the number of that ion present in a formula unit, and then the results are added, the sum must be zero.

Formation of Compounds: Additional Concepts Topic 6 Oxidation Numbers In the formula for an ionic compound, the symbol of the cation is written before that of the anion. Subscripts, or small numbers written to the lower right of the chemical symbols, show the numbers of ions of each type present in a formula unit.

Naming ionic compounds Formation of Compounds: Additional Concepts Topic 6 Naming ionic compounds In naming ionic compounds, name the cation first, then the anion. Monatomic cations use the element name. Monatomic anions use the root of the element name plus the suffix -ide. If an element can have more than one oxidation number, use a Roman numeral in parentheses after the element name, for example, iron(II) to indicate the Fe2+ ion. For polyatomic ions, use the name of the ion.

Naming ionic compounds Formation of Compounds: Additional Concepts Topic 6 Naming ionic compounds Certain polyatomic ions, called oxyanions, contain oxygen and another element. If two different oxyanions can be formed by an element, the suffix -ate is used for the oxyanion containing more oxygen atoms, and the suffix -ite for the oxyanion containing fewer oxygens. In the case of the oxyanions of the halogens, the following special rules are used.

Naming ionic compounds Formation of Compounds: Additional Concepts Topic 6 Naming ionic compounds four oxygens, per + root + -ate (example: perchlorate, ClO4–) three oxygens, root + -ate (example: chlorate, ClO3–)

Naming ionic compounds Formation of Compounds: Additional Concepts Topic 6 Naming ionic compounds two oxygens, root + -ite (example: chlorite, ClO2–) one oxygen, hypo- + root + -ite (example: hypochlorite, ClO–)

Naming ionic compounds Formation of Compounds: Additional Concepts Topic 6 Naming ionic compounds The formulas below are followed by their ionic compound. 1. NaBrO3 (sodium bromate) 2. Mg(NO3)2 (magnesium nitrate) 3. NH4ClO4 (ammonium perchlorate) 4. Al(ClO)3 (aluminum hypochlorite)

Metallic Bonds and Properties of Metals Formation of Compounds: Additional Concepts Topic 6 Metallic Bonds and Properties of Metals The bonding in metals is explained by the electron sea model, which proposes that the atoms in a metallic solid contribute their valence electrons to form a “sea” of electrons that surrounds metallic cations. These delocalized electrons are not held by any specific atom and can move easily throughout the solid. A metallic bond is the attraction between these electrons and a metallic cation.

Metallic Bonds and Properties of Metals Formation of Compounds: Additional Concepts Topic 6 Metallic Bonds and Properties of Metals Metals generally have extremely high boiling points because it is difficult to pull metal atoms completely away from the group of cations and attracting electrons.

Metallic Bonds and Properties of Metals Formation of Compounds: Additional Concepts Topic 6 Metallic Bonds and Properties of Metals Metals are also malleable (able to be hammered into sheets) and ductile (able to be drawn into wire) because of the mobility of the particles. The delocalized electrons make metals good conductors of electricity.

Metallic Bonds and Properties of Metals Formation of Compounds: Additional Concepts Topic 6 Metallic Bonds and Properties of Metals A mixture of elements that has metallic properties is called an alloy.

Additional Assessment Questions Topic 6 Question 1 What is the electron configuration, in abbreviated form, for nickel? Answer [Ar]4s23d8

Additional Assessment Questions Topic 6 Question 2 What structure has positive ions surrounded by negative ions, and the negative ions surrounded by positive ions? Answer a crystal lattice

Additional Assessment Questions Topic 6 Question 3 What is the correct formula for the ionic compound aluminum sulfate? Answer Al2(SO4)3

Practice Problems Topic 6 Question 1 Determine the correct formula for the ionic compound composed of the following pairs of ions.

Question 1a Answer 1a aluminum and carbonate Al2(CO3)3 Topic 6 Practice Problems Topic 6 Question 1a aluminum and carbonate Answer 1a Al2(CO3)3

Question 1b Answer 1b magnesium and carbonate MgCO3 Topic 6 Practice Problems Topic 6 Question 1b magnesium and carbonate Answer 1b MgCO3

Question 1c Answer 1c calcium and chlorate Ca(ClO3)2 Topic 6 Practice Problems Topic 6 Question 1c calcium and chlorate Answer 1c Ca(ClO3)2

Practice Problems Topic 6 Question 2 Name the following compounds.

Question 2a Answer 2a Co(OH)2 cobalt hydroxide Topic 6 Practice Problems Topic 6 Question 2a Co(OH)2 Answer 2a cobalt hydroxide

Question 2b Answer 2b Ag2CrO4 silver chromate Topic 6 Practice Problems Topic 6 Question 2b Ag2CrO4 Answer 2b silver chromate

Question 2c Answer 2c Na3PO4 sodium phosphate Topic 6 Practice Problems Topic 6 Question 2c Na3PO4 Answer 2c sodium phosphate