Forming and naming ionic compounds lab

Naming Ionic and Molecular Compounds Hands-On Labs, Inc. Version 42-0315-00-01

Review the safety materials and wear goggles when working with chemicals. Read the entire exercise before you begin. Take time to organize the materials you will need and set aside a safe work space in which to complete the exercise.

Experiment Summary:

You will apply the rules for naming ionic and molecular compounds to write the names of compounds when given the chemical formula. You will also write the formula for ionic and molecular compounds when given the name.

EXPERIMENT

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Learning Objectives Upon completion of this laboratory, you will be able to:

● Describe how the periodic table arranges elements by their chemical properties.

● Discuss the IUPAC naming system.

● Define molecular compound, ionic compound, polyatomic ion, oxidation state, and diatomic element.

● Identify the prefixes and suffixes used to name polyatomic ions and list the name, formula, and charge of common polyatomic ions.

● List the rules for converting formulas to names, and names to formulas for ionic and molecular compounds.

● Explain the difference between binary and oxoacids, and identify the rules for naming each.

● Generate a colored periodic table to distinguish between the groups of elements, and create a list of common polyatomic ions and strong acids to aid in naming chemical compounds.

● Write the names for ionic compounds, molecular compounds, polyatomic ions, and acids by interpreting their formulas.

● Write the chemical formula for ionic compounds, molecular compounds, polyatomic ions, and acids by interpreting their compound names.

Time Allocation: 3 hours

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Materials Student Supplied Materials

Quantity Item Description 1 Box of colored pencils or highlighters 1 Computer printer 1 Digital camera or smartphone 1 Package of note cards 1 Pen or pencil 1 Sheet of paper

Note: To fully and accurately complete all lab exercises, you will need access to:

1. A computer to upload digital camera images.

2. Basic photo editing software such as Microsoft® Word or PowerPoint®, to add labels, leader lines, or text to digital photos.

3. Subject-specific textbook or appropriate reference resources from lecture content or other suggested resources.

Note: The packaging and/or materials in this LabPaq kit may differ slightly from that which is listed above. For an exact listing of materials, refer to the Contents List included in your LabPaq kit.

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Background The Periodic Table

The periodic table is a reference for the arrangement of chemical elements. See Figure 1. The periodic table not only organizes the elements by their atomic number and electron configurations, it also organizes the elements by their chemical properties. The periodic table is the most important tool to have on hand when studying chemistry. A periodic table is located on the inside cover of almost every chemistry textbook.

Figure 1. Periodic Table of Elements. Click to Download Printable Version.

Communication skills are important in any field, and the language of chemistry has a vocabulary of its own. In the medical field, it is essential to communicate clearly and effectively. For example, it is important to be correct and unambiguous when transferring responsibility for a patient to another person, or asking the doctor or dentist for required medication. Reports may be written for the doctor or for communicating with a patient about their condition, and learning how to write chemical names and formulas is the first step in pharmacology.

For example, the ionic compound potassium nitrite (KNO2) is used to treat chest pain, whereas the compound potassium nitrate (KNO3) is used to treat asthma and is also found in toothpastes for sensitive teeth. A pharmacologist or doctor would need to ensure the proper indication of these compounds to properly and effectively treat a patient’s symptoms.

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o http://holscience.com/sites/default/files/Periodic_Table.pdf\
The IUPAC Naming System

The International Union of Pure and Applied Chemistry (IUPAC) naming system provides a systematic method of naming compounds around the globe. The IUPAC naming system was designed with the fundamental principle that “each different compound should have a different name.” Each IUPAC name for organic compounds consists of several parts: 3D relationship, numbered substituents, number of carbons in the longest chain, and the ending suffix that describes functional groups. Figure 2 shows the molecular structure for vitamin C, also called ascorbic acid. The formal, IUPAC name for the chemical is (5R)-5-[(1S)-1,2-dihydroxyethyl]-3,4-dihydroxyfuran-2(5H)-one.

Figure 2. The unique IUPAC name for ascorbic acid (vitamin C) includes the numbered constituents, 3D relationship of atoms, the number of carbons, and functional groups.

©Macrovector

The IUPAC naming system assures safety and consistency when using chemicals. It would be difficult to replicate experiments if scientists used different names for the same compound. Safety would also be a concern if there was no consistent system for naming because of the various hazards associated with mixing chemicals.

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Experiment Naming Ionic and Molecular Compounds

Naming Molecular Compounds

Molecular compounds consist of nonmetallic elements that share electrons through covalent bonds. The type of molecular compounds we will focus on naming in this lesson are binary molecular compounds. Binary molecular compounds consist of two nonmetal elements. For example, a water molecule (H2O) is a binary molecular compound consisting of the nonmetals hydrogen and oxygen.

To name a binary molecular compound, the first element is given its elemental name, and the second element is given its root (i.e. carb-, hydr-, ox-, fluor-) with the suffix “-ide.” For example:

● HF = hydrogen fluoride

Greek prefixes are used for molecular compounds to account for the number of each element in the compound. See Table 1 for the Greek prefixes that represent the numbers 1 - 10.

Table 1. Greek prefixes. Number of Atoms Prefix

1 Mono- 2 Di- 3 Tri- 4 Tetra- 5 Penta- 6 Hexa- 7 Hepta- 8 Octa- 9 Nona-

10 Deca-

For example:

● CO2 = carbon dioxide

● N2O3 = dinitrogen trioxide

The prefix “mono-” is never used for the first element, and only used for the second element if ambiguity exists in the naming. A few examples for using the prefix “mono-” on the second element are:

● carbon monoxide

● dinitrogen monoxide

● nitrogen monoxide

Note: If the final vowel in a prefix is “a” or “o” it is dropped before the vowel in a stem name, for ease of pronunciation.

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Converting a Molecular Compound Formula to a Name

Example 1: Writing a Nonmetal + Nonmetal Name: P2S5 1. Read the formula and look at the subscripts.

P2S5

Note that P and S are nonmetals, which can be determined by referencing a periodic table like the one in Figure 1.

2. Write the name of the first element with the correct Greek prefix.

P2 = diphosphorus

3. Write the root name of the second element with the suffix “-ide.”

S = sulfur = sulfide

4. Write the correct Greek prefix of the second element.

S5 = pentasulfide

5. Write the name of the molecular compound.

P2S5 = diphosphorus pentasulfide

Example 2: Writing a Nonmetal + Nonmetal Name: CO

1. Read the formula and look at the subscripts.

CO

2. Write the name of the first element with the correct Greek prefix. If the 1st element has the prefix “mono”, it is dropped.

C = carbon (NOT monocarbon)

3. Write the root name of the second element with the suffix “-ide.”

O = oxygen = oxide

4. Write the correct Greek prefix of the second element. If the final vowel in a prefix is “a” or “o” it is dropped before the vowel in a stem name, for ease of pronunciation.

O = monoxide (NOT monooxide)

5. Write the name of the molecular compound.

CO = carbon monoxide

Note: There is no charge indicated in the above formulas which indicates that they are molecular compounds and not ionic compounds.

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Converting a Name to a Molecular Compound Formula

Example 3: Writing a Nonmetal + Nonmetal Formula: Carbon Tetrafluoride

1. Read the name of the compound. carbon tetrafluoride

2. Write the first chemical symbol based on the first name written in the compound. carbon = C

3. Include the number of atoms based on the prefix (if any) included in the first name. 1 carbon atom = C

Note: Since the word “carbon” in carbon tetrafluoride has no prefix, it can be assumed that there is only one carbon atom in the molecule.

4. Write the second chemical symbol based on the second name written in the compound. fluoride = fluorine = F

5. Include the number of atoms based on the prefix (if any) included in the second name. tetrafluoride = 4 fluorine atoms = F4

6. Write the formula of the molecular compound. carbon tetrafluoride = CF4

Note: You will not be asked to “balance” the formula of molecular compounds because there are no ions to balance. Ionic charges and balancing equations will be introduced later.

Example 4: Writing a Nonmetal + Nonmetal Formula: Diboron Trioxide

1. Read the name of the compound. diboron trioxide

2. Write the first chemical symbol based on the first name written in the compound. boron = B

3. Include the number of atoms based on the prefix (if any) included in the first name. diboron = 2 boron atoms = B2

4. Write the second chemical symbol based on the second name written in the compound. oxide = oxygen = O

5. Include the number of atoms based on the prefix (if any) included in the second name.

trioxide = 3 oxygen atoms = O3

6. Write the formula of the molecular compound. diboron trioxide = B2O3

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Naming Ionic Compounds

Ionic compounds are chemical compounds containing both a cation (positive ion) and an anion (negative ion) held together by electrostatic forces, also known as ionic bonds. Ionic compounds are different from molecular compounds in that they usually contain a metal or an ammonium ion (NH4

+) and molecular compounds are composed of nonmetals. A binary ionic compound contains two elements, one metal and one nonmetal.

To name a binary ionic compound, the cation elemental name is listed first, followed by the root of the anion ending in “-ide.” For example:

● NaCl = sodium chloride

Greek prefixes are not used in naming the number of atoms of each element for ionic compounds. For example:

● Li3N = lithium nitride, NOT trilithium nitride.

Ionic compounds are written as neutral compounds, meaning the overall charge of the compound must equal zero. In order to determine the overall charge, the oxidation state of the metal and nonmetal must be known in order to ensure the correct number of atoms of each element are present in the compound. The oxidation state represents the number of electrons that an atom can gain, lose, or share when bonded with an atom of another element. The oxidation state for each element can be found on the periodic table in Figure 1. We will discuss how to use the oxidation state to calculate the number of atoms of a compound in further detail later.

Converting an Ionic Compound Formula to a Name

1. Use the periodic table to determine if a metal is present in the compound.

Note: Be aware that many elements have similar names and symbols.

a. If a metal is present, the compound is likely an ionic compound.

2. Determine if the metal ion (cation) has a “fixed charge.” A fixed charge means that there is only one possible oxidation state, as shown in Figure 3. Cations with a fixed charge include.

a. All elements in Group IA and Group IIA

b. Al3+

c. Transition metals with a fixed charge: Ag1+, Zn2+, and Cd2+

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Figure 3. The fixed charge oxidation states, or charges, of the element potassium (K) in Group IA and the element beryllium (Be) in Group IIA.

3. Proceed to step 6 if the metal does not have a fixed charge, otherwise continue to step 4.

4. Name the cation first.

a. Record the entire name of the cation.

5. Name the anion second.

a. Combine the root name of the nonmetal anion with the suffix “-ide.” The conversion from a formula to a name is complete once the anion has been named.

6. Determine the variable charges for the metal, as shown in Figure 4. Variable charge means that there is more than one possible oxidation state. Elements with a variable charge include:

a. All transition metals in Groups IIIA through IIB, EXCEPT: Ag1+, Zn2+, and Cd2+

b. All basic metals EXCEPT: Al3+

Figure 4. The variable charge oxidation states, or charges, that iron (Fe) and gold (Au) can carry.

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7. Name the cation first.

a. Include the entire name of the cation.

b. Balance the ionic charges of the cation and anion. Identify the number of ions required to generate a neutral compound.

c. List the Roman numeral in parentheses based on the ionic charge. Do not put a space between the cation name and the parentheses. For example, iron(III) chloride.

8. Name the anion second.

a. Include the root name of the anion and the suffix “-ide.”

Example 5: Writing a Metal + Nonmetal Name: Li2O

1. Read the formula and look at the subscripts.

Li2O

Note that Li is a metal and O is a nonmetal, which can be determined by referencing a periodic table like the one in Figure 1.

2. Determine if the metal ion has a fixed charge or variable charge.

Li = Group IA = fixed charge = 1+

3. Record the entire name of the cation.

Li = lithium

4. Write the root name of the nonmetal ion with the suffix “-ide.”

O = oxygen = oxide

5. Write the name of the ionic compound.

lithium oxide

Example 6: Writing a Metal + Nonmetal Name: Fe2O3 1. Read the formula and look at the subscripts.

Fe2O3 2. Determine if the metal ion has a fixed charge or variable charge.

Fe = Group VIIIB = variable charge = 2+ or 3+

3. Record the entire name of the cation.

Fe = iron

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4. Determine the Roman numeral by balancing the charges to create a neutral compound.

a. There are 2 atoms of iron and 3 atoms of oxygen.

b. We know oxygen always carries a 2- charge so all 3 atoms of oxygen have a 2- charge.

c. We need to determine if each iron atom has a 2+ or a 3+ charge by a simple algebraic calculation where the charge for each iron atom equals x and the equation is set to 0:

Tip: To balance Fe2O3, first consider the oxygen atoms. Oxygen always has a charge of 2-, therefore O3 has a total charge of 6-. This means that Fe2 must have a total charge of 6+. Each F atom will have a charge of 3+.

d. After solving for x, we find that each iron atom carries a 3+ charge. Thus, the Roman numeral used in the compound name is “III.”

iron(III)

5. Write the root name of the nonmetal ion with the suffix “-ide.”

O = oxygen = oxide

6. Write the name of the ionic compound.

iron(III) oxide

Converting a Name to an Ionic Compound Formula

When writing formulas for ionic compounds, the sum of the positive and negative charges MUST equal zero to obtain a neutral compound.

Example 7: Writing a Metal + Nonmetal Formula: Calcium Fluoride

1. Read the name of the compound.

calcium fluoride

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2. Determine if the metal ion has a fixed charge or variable charge.

calcium = Group IIA = fixed charge = 2+

Note: If the name does not include a Roman numeral, then the metal ion has a fixed charge.

3. Write the first chemical symbol based on the cation in the compound, including the charge.

calcium = Ca2+

4. Write the second chemical symbol based on the anion in the compound, including the charge.

fluoride = fluorine = F-

5. Balance the charges to determine the correct number of atoms of each element and write the formula for a neutral compound.

Tip: To balance CaF2, first consider the Ca has a fixed charge of 2+ and F carries a 1- charge. For the compound to have a net charge of 0, there must be two F atoms and one Ca atom.

6. Write the formula of the molecular compound.

calcium fluoride = CaF2

Example 8: Writing a Metal + Nonmetal Formula: Gold(III) Chloride

1. Read the name of the compound.

gold(III) chloride

2. Determine if the metal ion has a fixed charge or variable charge.

gold = Group IB = variable charge = 1+ or 3+

3. Write the first chemical symbol based on the cation in the compound, including the charge. The name tells us it is gold(III) meaning it carries a 3+ charge:

gold(III) = Au3+

4. Write the second chemical symbol based on the anion in the compound, including the charge.

chloride = chlorine = Cl-

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5. Balance the charges to determine the correct number of atoms of each element to write the formula for a neutral compound.

6. Write the formula of the molecular compound.

gold(III) chloride = AuCl3

Polyatomic Ions

Polyatomic ions are a group of two or more covalently bonded atoms that function as a single ion. For example, oxygen carries a 2- charge and hydrogen carries a 1+ charge. When combined they form a covalent bond, producing a single anion with a 1- charge called hydroxide (OH-). The 1- charge of the hydroxide ion is a product of the 2- charge of the O with the 1+ charge of the H (-2 + 1 = -1). Polyatomic ions are the fundamental unit in the majority of ionic compounds; therefore, knowing polyatomic ion names, formulas, and charges is important. Common ions and their charges are listed in Table 2.

Table 2. Common polyatomic ions.

Name Formula Charge

Ammonium NH4 + 1+

Hydroxide OH- 1-

Cyanide CN- 1-

Nitrite** NO2 - 1-

Nitrate** NO3 - 1-

Sulfite** SO3 2- 2-

Sulfate** SO4 2- 2-

Hydrogen sulfite** HSO3 - 1-

Hydrogen sulfate** HSO4 - 1-

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Name Formula Charge

Carbonate CO3 2- 2-

Hydrogen carbonate HCO3 - 1-

Phosphate PO4 3- 3-

Hydrogen phosphate HPO4 2- 2-

Dihydrogen phosphate H2PO4 - 1-

Hypochlorite ClO- 1-

Chlorite** ClO2 - 1-

Chlorate** ClO3 - 1-

Perchlorate ClO4 - 1-

Peroxide O2 2- 2-

Chromate*** CrO4 2- 2-

Dichromate*** Cr2O7 2- 2-

Permanganate*** MnO4 - 1-

**Note the very subtle differences in names and subscripts due to the oxidation states.

*** Note that permanganate, chromate, and dichromate each have a metal and a nonmetal.

Note: There are additional tables of polyatomic ions available online and in textbooks. This table includes only the most common ions encountered in general chemistry classes.

Here are a few helpful hints for naming polyatomic ions:

a. Suffixes: the name of the ion usually ends in “-ite” or “-ate.” A low oxidation state will have an ion ending in “-ite,” versus a higher oxidation state that ends in “-ate.” The oxidation state is dependent upon a calculation of the charges of the polyatomic ion. Figure 5 shows the calculations of the oxidation state for the sulfite ion (SO3

2-) and the sulfate ion (SO4

2-). A simple algebraic calculation is done to determine the oxidation state for each polyatomic ion by solving for “x” since we know that oxygen (O) carries a 2- charge:

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Figure 5. Algebraic calculations for the oxidation state of the polyatomic ions sulfite and sulfate.

b. Prefixes: “hypo-” indicates the very lowest oxidation state and “per-” indicates the very highest oxidation state. Figure 6 shows the calculations of the oxidation state for the hypochlorite ion (ClO-) and the perchlorate ion (ClO4

-). A simple algebraic calculation is done to determine the oxidation state for each polyatomic ion by solving for “x” since we know that oxygen (O) carries a 2- charge:

Figure 6. Algebraic calculations for the oxidation state of the polyatomic ions hypochlorite and perchlorate.