Writing and Naming Compounds

Writing and Naming Compounds

High School

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Learning Objectives

• Distinguish between ionic and covalent compounds based on their constituent elements.

• Name ionic compounds with transition metals and polyatomic ions using IUPAC rules.

• Write chemical formulas for ionic compounds by balancing the charges of their ions.

• Use the prefix system to correctly name binary covalent compounds.

• Determine the names and formulas for simple hydrocarbons like alkanes, alkenes, and alkynes.

Key Vocabulary

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Ionic Bond

A chemical bond created by the complete transfer of valence electrons from one atom to another.

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Covalent Bond

A chemical bond that involves the sharing of electron pairs between atoms, either equally or unequally.

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Polyatomic Ion

A charged group of two or more covalently bonded atoms that functions as a single ionic unit.

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Transition Metal

An element from the d-block of the periodic table that forms ions with different positive charges.

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Hydrocarbon

An organic compound consisting entirely of hydrogen and carbon atoms, forming the basis of organic chemistry.

Types of Chemical Bonds

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Ionic Bonds

• Electrons are transferred from a metal atom to a non-metal atom.

• This is caused by a large difference in electronegativity between atoms.

• An example is the bond in Sodium Chloride, forming NaCl.

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Covalent Bonds

• Electrons are shared between two or more non-metal atoms.

• Unequal electron sharing creates a polar covalent bond, like in H-F.

• Equal electron sharing creates a nonpolar covalent bond, like in Cl-Cl.

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Metallic Bonds

• These bonds are found exclusively between atoms in metallic elements.

• Valence electrons form a "sea" shared among a lattice of metal atoms.

• This structure allows metals to be malleable, ductile, and conduct electricity.

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Solved Example 1
Given Potassium (K) has an electronegativity of 0.8 and Fluorine (F) has an electronegativity of 4.0, calculate the difference and determine the type of chemical bond that forms between them.

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Step 1: Analyze and Sketch the Problem

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Solved Example 1
Given Potassium (K) has an electronegativity of 0.8 and Fluorine (F) has an electronegativity of 4.0, calculate the difference and determine the type of chemical bond that forms between them.

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Step 2: Solve for the Unknown

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Solved Example 1
Given Potassium (K) has an electronegativity of 0.8 and Fluorine (F) has an electronegativity of 4.0, calculate the difference and determine the type of chemical bond that forms between them.

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Step 3: Evaluate the Answer

• The calculated electronegativity difference of 3.2 is a large value, which indicates a high tendency for electron transfer.

• The bond forms between a metal (Potassium) and a non-metal (Fluorine), which typically results in an ionic bond. The answer is reasonable.

Multiple Choice

Based on electronegativity, what type of bond forms between a metal and a non-metal when electrons are fully transferred?

• Metallic Bond

• Nonpolar Covalent Bond

• Polar Covalent Bond

• Ionic Bond

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Naming Binary Ionic Compounds

• Binary ionic compounds are made of a metal and a non-metal.

• First, name the metal cation; its name does not change.

• Second, name the non-metal anion, changing the ending to “-ide.”

• So, the chemical formula NaCl is named Sodium Chloride.

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Solved Example 2
What is the chemical formula for an ionic compound made of aluminum and sulfur? Aluminum forms an ion with a +3 charge, and sulfur forms an ion with a -2 charge.

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Step 1: Analyze and Sketch the Problem

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Solved Example 2
What is the chemical formula for an ionic compound made of aluminum and sulfur? Aluminum forms an ion with a +3 charge, and sulfur forms an ion with a -2 charge.

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Step 2: Solve for the Unknown

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Solved Example 2
What is the chemical formula for an ionic compound made of aluminum and sulfur? Aluminum forms an ion with a +3 charge, and sulfur forms an ion with a -2 charge.

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Step 3: Evaluate the Answer

Multiple Choice

What is the correct chemical name for the ionic compound with the formula K₂S?

• Potassium (II) Sulfide

• Potassium Sulfide

• Dipotassium Sulfide

• Potassium Sulfur

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Writing Formulas for Ionic Compounds

• An ionic compound's formula must have balanced positive and negative charges to be neutral.

• Write the symbols and charges for the ions, like aluminum (Al³⁺) and oxygen (O^2-).

• "Cross over" the charge numbers to make them the subscripts for the other ion.

• The final formula is Al₂O₃, balancing the charges: (2 × +3) + (3 × -2) = 0.

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Multiple Choice

Following the rules for balancing charges, what is the correct chemical formula for a compound formed from beryllium (Be²⁺) and bromide (Br^-)?

• Be₂Br

• Be₂Br₃

• BeBr

• BeBr₂

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Ionic Compounds with Transition Metals

• Transition metals can form ions with multiple charges, like Cu⁺ and Cu²⁺.

• ​A Roman numeral after the metal’s name shows its specific charge.

• In CuCl₂, copper has a +2 charge, so it is named copper(II) chloride.

• In PbBr₄, lead has a +4 charge, so it is named lead(IV) bromide.

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Solved Example 4
What is the chemical formula for iron(III) oxide?

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Step 1: Analyze and Sketch the Problem

• Goal: To write the correct chemical formula for iron(III) oxide.

• Knowns: The cation is iron (Fe) and the anion is oxide (O). The Roman numeral (III) tells us the charge of the iron ion is +3. Oxygen is in group 16, so its ion has a -2 charge.

• Ions: Fe³⁺ and O^2-.

• Unknown: The subscripts for each element in the neutral compound.

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Solved Example 4
What is the chemical formula for iron(III) oxide?

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Step 2: Solve for the Unknown

• Use the "criss-cross" method to balance the charges. The numerical value of the cation's charge becomes the subscript for the anion, and the numerical value of the anion's charge becomes the subscript for the cation.

• The +3 charge on iron becomes the subscript for oxygen, and the -2 charge on oxygen becomes the subscript for iron. This gives the formula: Fe₂O₃.

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Solved Example 4
What is the chemical formula for iron(III) oxide?

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Step 3: Evaluate the Answer

• Check that the total charge of the compound is zero.

• Total positive charge from iron: 2 ions × (+3 charge/ion) = +6.

• Total negative charge from oxide: 3 ions × (-2 charge/ion) = -6.

• The total charge is (+6) + (-6) = 0. The formula is correct.

Multiple Choice

What is the charge of the iron ion in the compound named iron(III) bromide?

• -3

• +2

• +3

• 0

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Compounds with Polyatomic Ions

• A polyatomic ion is a group of atoms acting as one unit with a charge, like NO₃^-.

• Name the compound using the ion's name, so Na₃PO₄ is called sodium phosphate.

• A hydrate is an ionic compound with water, named using a prefix for water molecules.

• Balance charges to write formulas, like Mg₃(PO₄)₂, using parentheses around the ion.

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Solved Example 5
What is the chemical formula for the ionic compound formed between calcium (Ca²⁺) and the nitrate ion (NO₃^-)?

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Step 1: Analyze and Sketch the Problem

• Goal: To write the correct chemical formula for calcium nitrate.

• Knowns: The cation is calcium (Ca²⁺) with a charge of +2. The polyatomic anion is nitrate (NO₃^-) with a charge of -1.

• Unknown: The chemical formula for the neutral compound.

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Solved Example 5
What is the chemical formula for the ionic compound formed between calcium (Ca²⁺) and the nitrate ion (NO₃^-)?

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Step 2: Solve for the Unknown

• Write the ion symbols, Ca²⁺ and NO₃^-. Then, use the “cross-over” method, where the charge of each ion becomes the subscript for the other ion.

• This results in the formula Ca₁(NO₃)₂. Since subscripts of 1 are omitted, the final correct formula is Ca(NO₃)₂.

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Solved Example 5
What is the chemical formula for the ionic compound formed between calcium (Ca²⁺) and the nitrate ion (NO₃^-)?

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Step 3: Evaluate the Answer

• The formula is Ca(NO₃)₂. Let's check the total charge.

• Charge from calcium: 1 × (+2) = +2.

• Charge from nitrate: 2 × (-1) = -2.

• The total charge of the compound is (+2) + (-2) = 0. The formula is correct because the compound is neutral.

Multiple Choice

What is the correct name for the compound with the formula NH₄Cl?

• Ammonium(I) chloride

• Ammonium chloride

• Ammonium chlorate

• Nitrogen hydride chloride

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Naming Binary Covalent Compounds

• Binary covalent compounds are formed between two non-metal elements.

• A prefix shows the number of atoms: di- (2), tri- (3), tetra- (4).

• The first element gets a prefix only if more than one atom is present.

• The second element always gets a prefix and its ending changes to -ide. For example, SF₆ is sulfur hexafluoride and P₄O₁₀ is tetraphosphorus decoxide.

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Solved Example 6
Given the IUPAC name dinitrogen trioxide, what is its chemical formula? Use the prefix system to determine the number of atoms for each element.

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Step 1: Analyze and Sketch the Problem

• Goal: Determine the chemical formula from the compound's name.

• Knowns: The name is dinitrogen trioxide. Prefixes indicate atom count: "di-" means 2, and "tri-" means 3.

• Unknown: The chemical formula.

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Solved Example 6
Given the IUPAC name dinitrogen trioxide, what is its chemical formula? Use the prefix system to determine the number of atoms for each element.

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Step 2: Solve for the Unknown

• Identify the elements and prefixes: "Dinitrogen" indicates two nitrogen (N) atoms, and "trioxide" indicates three oxygen (O) atoms.

• Combine the element symbols with their respective counts as subscripts to get the final chemical formula: N₂O₃.

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Solved Example 6
Given the IUPAC name dinitrogen trioxide, what is its chemical formula? Use the prefix system to determine the number of atoms for each element.

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Step 3: Evaluate the Answer

• Review the derived formula N₂O₃.

• N₂ corresponds to the prefix "di-" for nitrogen, and O₃ corresponds to the prefix "tri-" for oxygen (oxide). The formula correctly represents the name dinitrogen trioxide.

Multiple Choice

What is the correct name for the covalent compound PBr₃?

• Monophosphorus tribromide

• Phosphorus(III) bromide

• Phosphorus tribromide

• Phosphorus bromide

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Writing Formulas for Covalent Compounds

• Prefixes in a name become the subscripts in the chemical formula.

• ​For dihydrogen monoxide, "di-" means two hydrogen atoms, giving the formula H₂O.

• For arsenic trioxide, "tri-" means three oxygen atoms, creating the formula AsO₃.

• No prefix on the first element, as in arsenic, means one atom.

Multiple Choice

Based on the prefix system, what is the chemical formula for oxygen difluoride?

• O₂F₂

• O₂F

• OF

• OF₂

Naming Simple Hydrocarbons

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Alkanes (-ane)

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Alkenes (-ene)

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Alkynes (-yne)

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Solved Example 8
An alkane contains 7 carbon atoms. Using the prefix 'hept-' and the suffix '-ane', determine its chemical name and write the correct chemical formula for this hydrocarbon.

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Step 1: Analyze and Sketch the Problem

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Solved Example 8
An alkane contains 7 carbon atoms. Using the prefix 'hept-' and the suffix '-ane', determine its chemical name and write the correct chemical formula for this hydrocarbon.

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Step 2: Solve for the Unknown

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Solved Example 8
An alkane contains 7 carbon atoms. Using the prefix 'hept-' and the suffix '-ane', determine its chemical name and write the correct chemical formula for this hydrocarbon.

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Step 3: Evaluate the Answer

Multiple Choice

What is the correct name for a hydrocarbon with the chemical formula C₄H₁₀?

• Butyne

• Tetrane

• Butane

• Butene

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Common Misconceptions in Naming Compounds

Misconception	Correction
Prefixes like di- and tri- are used for all compounds.	These prefixes are only for covalent compounds (two non-metals).
All transition metals need a Roman numeral in their name.	Exceptions like Zinc (Zn) and Silver (Ag) have fixed charges.
The ending of a polyatomic ion's name changes to "-ide".	The name of the polyatomic ion is used as is.
The formula for all hydrocarbons is the same.	The formula depends on if it’s an alkane, alkene, or alkyne.

Multiple Choice

Why is the compound CaCl₂ named "calcium chloride" while SnCl₂ is named "tin(II) chloride"?

• The "(II)" indicates there are two atoms, not the charge.

• Covalent naming rules apply to calcium, while ionic rules apply to tin.

• Calcium is a main group metal with a fixed charge, while tin is a transition metal with a variable charge.

• Both should be named with prefixes as "calcium dichloride" and "tin dichloride".

Multiple Choice

What is the correct chemical formula for the compound manganese(III) sulfite?

• Mn₃(SO₃)₂

• Mn₂(SO₃)₃

• Mn(SO₃)₃

• MnSO₃

Multiple Choice

Analyze the compound with the formula Sr₃N₂. What is its name and why are prefixes not used?

• Strontium nitride; prefixes are optional and were left out for simplicity.

• Strontium nitride; it is an ionic compound between a metal and non-metal, so charges are balanced without prefixes.

• Strontium(II) nitride; strontium is a transition metal and requires a Roman numeral.

• Tristrontium dinitride; prefixes are required to show the number of atoms for all compounds.

Multiple Choice

A compound is named "dinitrogen pentoxide". What does this name allow you to conclude about its bonding and chemical formula?

• It is an ionic compound with the formula N₂O₅ because nitrogen has a +5 charge.

• It is an ionic compound and should be named "nitrogen(V) oxide".

• It is a covalent compound with the formula N₂O₅ because prefixes indicate it's formed between two non-metals.

• It is a covalent compound with the formula N₅O₂.

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Summary

• Name ionic compounds with the metal, then non-metal (-ide); use Roman numerals for transition metals.

• Use special names for polyatomic ions and balance charges to write the formula.

• Name covalent compounds using prefixes (di-, tri-) to show the number of atoms.

• Name hydrocarbons with a prefix for carbon atoms and a suffix for bond type.

Poll

On a scale of 1-4, how confident are you about writing and naming chemical compounds after this review?

• 1

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• 4