Topic 7 Topic 7

Properties and Naming of Ionic Bonds Table of Contents Topic 7 Topic 7

The submicroscopic structure of ionic compounds helps explain why they share certain macroscopic properties such as high melting points, brittleness, and the ability to conduct electricity when molten or when dissolved in water. Ionic Compounds Types of Compounds: Basic Concepts You have learned that ionic compounds are made up of oppositely charged ions held together strongly in well-organized units. Topic 7 Topic 7

Ionic Compounds Because of their structure, they usually are hard solids at room temperature and are difficult to melt. Look at the structure of magnesium oxide. Topic 7 Topic 7 Types of Compounds: Basic Concepts

Ionic Compounds When ionic compounds melt or dissolve in water, their three-dimensional structure breaks apart, and the ions are released from the structure. Topic 7 Topic 7 Types of Compounds: Basic Concepts

Ionic Compounds These charged ions are now free to move and can conduct an electrical current. Topic 7 Topic 7 Types of Compounds: Basic Concepts

Binary Ionic Compounds Formulas are part of the language that is used to communicate information about substances. As a first step in studying this new language, you will learn how to name and write formulas for ionic compounds. Topic 7 Topic 7 Types of Compounds: Basic Concepts

Binary Ionic Compounds Sodium chloride (NaCl) contains only sodium and chlorine, and potassium iodide (KI) contains only potassium and iodine. Each is an example of a binary compound, which is a compound that contains only two elements. Topic 7 Topic 7 Types of Compounds: Basic Concepts

Binary Ionic Compounds Binary ionic compounds can contain more than one ion of each element, as in CaF 2, but they are not composed of three or more different elements, as are more complex compounds. Topic 7 Topic 7 Types of Compounds: Basic Concepts

Binary Ionic Compounds To name a binary ionic compound, first write the name of the positively charged ion, usually a metal, and then add the name of the nonmetal or negatively charged ion, whose name has been modified to end in -ide. The compound formed from potassium and chlorine is called potassium chloride. Magnesium combines with oxygen to form a compound called magnesium oxide. Topic 7 Topic 7 Types of Compounds: Basic Concepts

Binary Ionic Compounds You are already familiar with one formula for an ionic compound—NaCl. You have learned that compounds are electrically neutral. Sodium chloride contains sodium ions that have a 1+ charge and chloride ions that have a 1– charge. Topic 7 Topic 7 Types of Compounds: Basic Concepts

Binary Ionic Compounds This means that the sum of the charges in an ionic compound must always equal zero. Thus, one Na + balances one Cl – in sodium chloride. Topic 7 Topic 7 Types of Compounds: Basic Concepts

Binary Ionic Compounds When you write a formula, you add subscripts to the symbols for the ions until the algebraic sum of the ions’ charges is zero. The smallest subscript to both ions that results in a total charge of zero is 1. However, no subscript needs to be written because it is understood that only one ion or atom of an element is present if there is no subscript. Topic 7 Topic 7 Types of Compounds: Basic Concepts

Binary Ionic Compounds The formula NaCl indicates that sodium chloride contains sodium and chloride ions, that there is one sodium ion present for every chloride ion in the compound, and that the compound has no overall charge. Topic 7 Topic 7 Types of Compounds: Basic Concepts

Binary Ionic Compounds If more than one ion of a given element is present in a compound, the subscript indicates how many ions are present. The mineral known as fluorite is calcium fluoride, which has the formula CaF 2. This formula indicates that there is one calcium ion for every two fluoride ions in the compound. Topic 7 Topic 7 Types of Compounds: Basic Concepts

Binary Ionic Compounds In an ionic compound, a formula represents the smallest ratio of atoms or ions in the compound. Topic 7 Topic 7 Types of Compounds: Basic Concepts

Binary Ionic Compounds This simplest ratio of ions in a compound is called a formula unit. Each formula unit of calcium fluoride consists of one calcium ion and two fluoride ions. Each of the three ions has a stable octet configuration of electrons, and the formula unit has no overall charge. Topic 7 Topic 7 Types of Compounds: Basic Concepts

Predicting Charge on Ions The noble gases each have eight electrons in their outer-energy levels. Metals have few outer-level electrons so they tend to lose them and become positive ions. Sodium must lose just one electron, becoming an Na + ion. Calcium must lose two electrons, becoming a Ca 2+ ion. Topic 7 Topic 7 Types of Compounds: Basic Concepts

Predicting Charge on Ions Most nonmetals, on the other hand, have outer-energy levels that contain four to seven electrons, so they tend to gain electrons and become negative ions. Topic 7 Topic 7 Types of Compounds: Basic Concepts

Predicting Charge on Ions Because all elements in a given group have the same number of electrons in their outer- energy level, they must lose or gain the same number of electrons to achieve a noble-gas electron configuration. Metals always lose electrons and nonmetals always gain electrons when they form ions. The charge on the ion is known as the oxidation number of the atom. Topic 7 Topic 7 Types of Compounds: Basic Concepts

Predicting Charge on Ions The oxidation numbers for many elements in the main groups are arranged by group number. Topic 7 Topic 7 Types of Compounds: Basic Concepts

Predicting Charge on Ions Oxidation numbers for elements in Groups 3 through 12, the transition elements, cannot be predicted by group number. Topic 7 Topic 7 Types of Compounds: Basic Concepts

Predicting Charge on Ions Aluminum is in Group 13, so it loses its three outer electrons to become an Al 3+ ion; oxygen is in Group 16 and has six valence electrons, so it gains two electrons to become an O 2– ion. Topic 7 Topic 7 Types of Compounds: Basic Concepts

Predicting Charge on Ions Notice that one of aluminum’s three electrons has not been taken up by the oxygen atom. Because all the electrons must be accounted for, more than one oxygen atom must be involved in the reaction. Topic 7 Topic 7 Types of Compounds: Basic Concepts

Predicting Charge on Ions But, oxygen cannot gain only one electron, so a second aluminum atom must be present to contribute a second electron to oxygen. In all, two Al 3+ ions must combine with three O 2– ions to form Al 2 O 3. Remember that the charges in the formula for aluminum oxide must add up to zero. Topic 7 Topic 7 Types of Compounds: Basic Concepts

Compounds Containing Polyatomic Ions The ions you have studied thus far have contained only one element. However, some ions contain more than one element. An ion that has two or more different elements is called a polyatomic ion. Although the individual atoms have no charge, the group as a whole has an overall charge. Topic 7 Topic 7 Types of Compounds: Basic Concepts

Compounds Containing Polyatomic Ions Topic 7 Topic 7 Types of Compounds: Basic Concepts

Compounds Containing Polyatomic Ions Topic 7 Topic 7 Types of Compounds: Basic Concepts

Ionic compounds may contain positive metal ions bonded to negative polyatomic ions, such as in NaOH; negative nonmetal ions bonded to positive polyatomic ions, such as in NH 4 I; or positive polyatomic ions bonded to negative polyatomic ions, such as in NH 4 NO 3. Compounds Containing Polyatomic Ions Topic 7 Topic 7 Types of Compounds: Basic Concepts

To write the formula for an ionic compound containing one or more polyatomic ions, simply treat the polyatomic ion as if it were a single-element ion by keeping it together as a unit. Remember that the sum of the positive and negative charges must equal zero. Compounds Containing Polyatomic Ions Topic 7 Topic 7 Types of Compounds: Basic Concepts

Multiples of a polyatomic ion in a formula can be indicated by placing the entire polyatomic ion, without the charge, in parentheses. Write a subscript outside the parentheses to show the number of polyatomic ions in the compound. Never change the subscripts within the polyatomic ion. Compounds Containing Polyatomic Ions Topic 7 Topic 7 Types of Compounds: Basic Concepts

To do so would change the composition of the ion. The formula for the compound that contains one magnesium ion and two nitrate ions is Mg(NO 3 ) 2. Compounds Containing Polyatomic Ions Topic 7 Topic 7 Types of Compounds: Basic Concepts

To name a compound containing a polyatomic ion, follow the same rules as used in naming binary compounds. Name the positive ion first, followed by the negative ion. Compounds Containing Polyatomic Ions Topic 7 Topic 7 Types of Compounds: Basic Concepts

The name of the compound composed of calcium and the carbonate ion is calcium carbonate. However, do not change the ending of the negative polyatomic ion name. Compounds Containing Polyatomic Ions Topic 7 Topic 7 Types of Compounds: Basic Concepts

To form a neutral compound, one Ca 2+ ion must combine with one CO 3 2– ion to give the formula CaCO 3. Calcium is in Group 2, so its ion has a 2+ charge. The carbonate ion has a 2– charge. Compounds Containing Polyatomic Ions Topic 7 Topic 7 Types of Compounds: Basic Concepts

Compounds of Transition Elements Transition elements form positive ions just as other metals do, but most transition elements can form more than one type of positive ion. Elements known as transition elements are located in Groups 3 through 12 in the periodic table. In other words, transition elements can have more than one oxidation number. Topic 7 Topic 7 Types of Compounds: Basic Concepts

Zinc and silver are two exceptions to the variability of other transition elements; each forms one type of ion. For example, copper can form both Cu + and Cu 2+ ions, and iron can form both Fe 2+ and Fe 3+ ions. The zinc ion is Zn 2+ and the silver ion is Ag +. Compounds of Transition Elements Topic 7 Topic 7 Types of Compounds: Basic Concepts

They do this by using a Roman numeral to indicate the oxidation number of a transition element ion. Chemists must have a way to distinguish the names of compounds formed from the different ions of a transition element. Compounds of Transition Elements Topic 7 Topic 7 Types of Compounds: Basic Concepts Click box to view movie clip.

No additional naming system is needed for zinc and silver compounds because their formulas are not ambiguous. This Roman numeral is placed in parentheses after the name of the element. Compounds of Transition Elements Topic 7 Topic 7 Types of Compounds: Basic Concepts

Compounds of Transition Elements Topic 7 Topic 7 Types of Compounds: Basic Concepts

Compounds of Transition Elements Topic 7 Topic 7 Types of Compounds: Basic Concepts

Compounds of Transition Elements Topic 7 Topic 7 Types of Compounds: Basic Concepts

Hydrates A compound in which there is a specific ratio of water to ionic compound is called a hydrate. Many ionic compounds are prepared by crystallization from a water solution, and water molecules become a part of the crystal. In a hydrate, the water molecules are chemically bonded to the ionic compound. Topic 7 Topic 7 Types of Compounds: Basic Concepts

Hydrates These compounds are called hygroscopic substances, and one example is sodium carbonate (Na 2 CO 3 ). Some ionic compounds can easily become hydrates by absorbing water molecules from water vapor in the air. In a hydrate, the water molecules are chemically bonded to the ionic compound. Topic 7 Topic 7 Types of Compounds: Basic Concepts

Hydrates Substances that are so hygroscopic that they take up enough water from the air to dissolve completely and form a liquid solution are called deliquescent. Topic 7 Topic 7 Types of Compounds: Basic Concepts

Hydrates To write the formula for a hydrate, write the formula for the compound and then place a dot followed by the number of water molecules per formula unit of compound. The dot in the formula represents a ratio of compound formula units to water molecules. For example, CaSO 4 2H 2 0 is the formula for a hydrate of calcium sulfate that contains two molecules of water for each formula unit of calcium sulfate. Topic 7 Topic 7 Types of Compounds: Basic Concepts

Hydrates To name hydrates, follow the regular name for the compound with the word hydrate, to which a prefix has been added to indicate the number of water molecules present. Topic 7 Topic 7 Types of Compounds: Basic Concepts

Hydrates The name of the compound with the formula CaSO4 2H 2 O is calcium sulfate dihydrate. Topic 7 Topic 7 Types of Compounds: Basic Concepts

Hydrates Heating hydrates can drive off the water. This results in the formation of an anhydrous compound—one in which all of the water has been removed. In some cases, an anhydrous compound may have different color from that of its hydrate. Topic 7 Topic 7 Types of Compounds: Basic Concepts

Basic Assessment Questions Question 1 Determine the ratio of the atoms in the ionic compound formed in each case. A. aluminum (Al) and fluorine (F) B. lithium (Li) and oxygen (O) Topic 7 Topic 7

Basic Assessment Questions Answers A. aluminum (Al) and fluorine (F) B. lithium (Li) and oxygen (O) one AL for every three F two Li for every O Topic 7 Topic 7

Basic Assessment Questions Write the correct formula for the ionic compound formed between atoms of each of the following pairs of elements. A. sodium (Na) and sulfur (S) Question 2 B. magnesium (Mg) and nitrogen (N) Topic 7 Topic 7

Basic Assessment Questions A. sodium (Na) and sulfur (S) Answers B. magnesium (Mg) and nitrogen (N) Na 2 S Mg 3 N 2 Topic 7 Topic 7

Types of Compounds: Additional Concepts Forming Chemical Bonds Elements tend to react so as to achieve the stable electron configuration of a noble gas, typically an octet of electrons. 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. The periodic table is useful in predicting the charges of ions typically formed by various atoms. Topic 7 Topic 7

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. Types of Compounds: Additional Concepts Topic 7 Topic 7

This arrangement, which involves strong attraction between oppositely charged ions, tends almost always to produce certain properties, such as high melting and boiling points and brittleness. Properties of Ionic Compounds and Lattice Energy Types of Compounds: Additional Concepts Topic 7 Topic 7

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. Properties of Ionic Compounds and Lattice Energy Types of Compounds: Additional Concepts Topic 7 Topic 7

The combination of these conductivity characteristics is a very good identifier of ionic compounds, although each characteristic separately is not very reliable. Properties of Ionic Compounds and Lattice Energy Types of Compounds: Additional Concepts Topic 7 Topic 7

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 Types of Compounds: Additional Concepts Topic 7 Topic 7

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 Types of Compounds: Additional Concepts Topic 7 Topic 7 Click box to view movie clip.

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. Types of Compounds: Additional Concepts Topic 7 Topic 7

Naming Ionic Compounds four oxygens, per + root +-ate (example: perchlorate, ClO 4 – ) three oxygens, root + -ate (example: chlorate, ClO 3 – ) two oxygens, root + -ite (example: chlorite, ClO 2 – ) one oxygen, hypo- + root + -ite (example: hypochlorite, ClO – ) Types of Compounds: Additional Concepts Topic 7 Topic 7

Additional Assessment Questions For each of the following atoms, write the formula of the ion the atom is most likely to form and identify that ion as a cation or an anion. Questions 1 A. bromine (Br), element 35 B. gallium (Ga), element 31 Topic 7 Topic 7

Answers A. bromine (Br), element 35 Br – anion B. gallium (Ga), element 31 Ga 3 cation Topic 7 Topic 7 Additional Assessment Questions

Name the ionic Compounds that have the following formulas. Question 2 B. KHSO 4 A. Mg(NO 3 ) 2 Topic 7 Topic 7 Additional Assessment Questions

Answers B. KHSO 4 A. Mg(NO 3 ) 2 magnesium nitrate potassium hydrogen sulfate Topic 7 Topic 7 Additional Assessment Questions