Topic 6.

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Topic 6

Topic 6: Formation of Compounds
Table of Contents Topic 6 Topic 6: Formation of Compounds Basic Concepts Additional Concepts

Salt: A Familiar Compound
Formation of Compounds: Basic Concepts Topic 6 Salt: A Familiar Compound Sodium chloride occurs naturally in large, solid, underground deposits throughout the world and is dissolved in the world’s oceans. Salt can be obtained by mining these solid deposits, and by the evaporation of seawater.

Physical Properties of Salt
Formation of Compounds: Basic Concepts Topic 6 Physical Properties of Salt Table salt is a white solid at room temperature. If sodium chloride is heated to a temperature of about 800°C, it melts and forms liquid salt. Solid sodium chloride does not conduct electricity, but melted sodium chloride does. Salt also dissolves easily in water. The resulting solution is an excellent conductor of electricity.

Chemical Properties of Salt
Formation of Compounds: Basic Concepts Topic 6 Chemical Properties of Salt Salt does not react readily with other substances. Properties of Sodium Sodium is a shiny, silvery-white, soft, solid element.

Sodium melts to form a liquid when it is heated above 98°C.
Formation of Compounds: Basic Concepts Topic 6 Properties of Sodium Sodium melts to form a liquid when it is heated above 98°C. Sodium must be stored under oil because it reacts with oxygen and water vapor in the air. Because of its high reactivity, the free element sodium is never found in the environment.

Properties of Chlorine
Formation of Compounds: Basic Concepts Topic 6 Properties of Chlorine The element chlorine, is a pale green, poisonous gas with a choking odor. Like sodium, it is among the most reactive of the elements and must be handled with extreme care. Because chlorine is slightly soluble in water, it is an excellent disinfectant for swimming pools.

Composition of Inhaled and Exhaled Air
Formation of Compounds: Basic Concepts Topic 6 Composition of Inhaled and Exhaled Air The mixture of gases that you exhale contains more than 100 times the amount of carbon dioxide that was in the air that you inhaled.

Physical Properties of Carbon Dioxide
Formation of Compounds: Basic Concepts Topic 6 Physical Properties of Carbon Dioxide Carbon dioxide is a colorless, odorless, and tasteless gas. When carbon dioxide is cooled below 280°C, the gas changes directly to white, solid carbon dioxide without first becoming a liquid.

Physical Properties of Carbon Dioxide
Formation of Compounds: Basic Concepts Topic 6 Physical Properties of Carbon Dioxide Because the solid form of carbon dioxide does not melt to a liquid, it is called dry ice.

The Properties of Carbon
Formation of Compounds: Basic Concepts Topic 6 The Properties of Carbon Carbon is a nonmetal and is fairly unreactive at room temperature. However, at higher temperatures, it reacts with many other elements. The majority of compounds that make up living things contain carbon.

The Properties of Oxygen
Formation of Compounds: Basic Concepts Topic 6 The Properties of Oxygen Oxygen is another nonmetal. It is a colorless, odorless, and tasteless gas that makes up about 21 percent of the air you breathe. Oxygen gas becomes a liquid when it is cooled to –183°C, and it is slightly soluble in water. Oxygen is more reactive than carbon. A prime example of its reactivity is the process of rusting, in which the element iron combines with oxygen from air.

Elemental Composition of Earth’s Crust
Formation of Compounds: Basic Concepts Topic 6 Elemental Composition of Earth’s Crust Referring to the circle graph, one can see that oxygen is the most abundant element in Earth’s crust. Nearly all of this oxygen occurs in compounds with other elements.

Physical Properties of Water
Formation of Compounds: Basic Concepts Topic 6 Physical Properties of Water Water covers approximately 70 percent of Earth’s surface and also makes up about 70 percent of the mass of the average human body. Water is the only one of the three compounds that occurs in Earth’s environment in all three states of matter.

Physical Properties of Water
Formation of Compounds: Basic Concepts Topic 6 Physical Properties of Water Liquid water boils into gaseous water (steam) at 100°C and freezes to solid water (ice) at 0°C. It is often called the universal solvent in recognition of this valuable property.

Chemical Properties of Water
Formation of Compounds: Basic Concepts Topic 6 Chemical Properties of Water Water is a stable compound, and acts as a medium in which chemical reactions occur.

The Properties of Hydrogen
Formation of Compounds: Basic Concepts Topic 6 The Properties of Hydrogen Hydrogen is the lightest and most abundant element in the universe. Hydrogen is usually classified as a nonmetal. Hydrogen is a reactive element. It occurs in a variety of compounds, particularly water. Hydrogen reacts vigorously with many elements, including oxygen. Hydrogen does not conduct electricity and is only slightly soluble in water.

Chemical Reactions Topic 6 Formation of Compounds: Basic Concepts
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Formation of Compounds: Basic Concepts
Topic 6 The Octet Rule 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.

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).

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.

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.

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.

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.

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 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 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 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.

Formation of Water by Electron Sharing
Formation of Compounds: Basic Concepts Topic 6 Formation of Water by Electron Sharing The stability of the atoms in a water molecule results from a cooperative arrangement in which the eight valence electrons (six from oxygen and one each from two hydrogens) are distributed among the three atoms.

Formation of Compounds: Basic Concepts Topic 6 Formation of Water by Electron Sharing By sharing an electron pair with the oxygen, each hydrogen claims two electrons in its outer level.

Formation of Compounds: Basic Concepts Topic 6 Formation of Water by Electron Sharing The oxygen, by sharing two electrons with two hydrogens, claims a stable octet in its outer level. By this method, each atom achieves a stable noble gas configuration.

Click box to view movie clip.
Formation of Compounds: Basic Concepts Topic 6 Electron Sharing Produces Molecules The attraction of two atoms for a shared pair of electrons is called a covalent bond. Notice that in a covalent bond, atoms share electrons and neither atom has an ionic charge. Click box to view movie clip.

Electron Sharing Produces Molecules
Formation of Compounds: Basic Concepts Topic 6 Electron Sharing Produces Molecules A compound whose atoms are held together by covalent bonds is a covalent compound. Water is a covalent compound.

Electron Sharing Produces Molecules
Formation of Compounds: Basic Concepts Topic 6 Electron Sharing Produces Molecules A molecule is an uncharged group of two or more atoms held together by covalent bonds. Ethanol, also known as ethyl alcohol, is a typical covalent compound.

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.

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.

Additional Concepts Topic 6
Formation of Compounds: Additional Concepts Topic 6 Additional Concepts

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.

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.

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.

Formation of Compounds: Additional Concepts Topic 6 Properties of ionic compounds and lattice energy Based on the properties of the following “unknowns,” each is classified as either ionic or not ionic. Ionic Not Ionic has a high boiling point and shatters when hammered conducts electricity when liquid and has a low melting point has a high melting point and conducts electricity when dissolved in water conducts electricity when solid

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.

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.

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–.

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.

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.

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–)

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–)

Formation of Compounds: Additional Concepts Topic 6 Naming ionic compounds The formulas below are followed by their ionic compound. 1. NaBrO (sodium bromate) 2. Mg(NO3)2 (magnesium nitrate) 3. NH4ClO (ammonium perchlorate) 4. Al(ClO) (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.

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.

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.

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. Alloys can be of two basic types. A substitutional alloy is one in which atoms of the original metal are replaced by other atoms of similar size. An interstitial alloy is one in which the small holes in a metallic crystal are filled by other smaller atoms.

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

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

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

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