Problem 125 - Chemistry Matter and Change

Question

Name each molecule. $$ \begin{array}{l}{\text { a. } \mathrm{PCl}_{3}} \\ {\text { b. } \mathrm{Cl}_{2} \mathrm{O}_{7}} \\ {\text { c. } \mathrm{P}_{4} \mathrm{O}_{6}} \\ {\text { d. } \mathrm{NO}}\end{array} $$

Step-by-Step Solution

Answer

a. Phosphorus trichloride; b. Dichlorine heptoxide; c. Tetraphosphorus hexoxide; d. Nitrogen monoxide.

Step 1: Identify the Molecular Formula

Examine each compound to identify the type of atoms present and their respective quantities.- For compound (a), the formula is \( \text{PCl}_3 \).- For compound (b), the formula is \( \text{Cl}_2 \text{O}_7 \).- For compound (c), the formula is \( \text{P}_4 \text{O}_6 \).- For compound (d), the formula is \( \text{NO} \).

Step 2: Apply Common Naming System

For each compound, use the common naming convention for covalent (molecular) compounds: - Use prefixes to denote the number of each type of atom in the compound. - The first element in the compound name remains unchanged unless it should include a prefix indicating multiple atoms. - The second element ends with the suffix 'ide.'

Step 3: Name Compound a: \( \text{PCl}_3 \)

For \( \text{PCl}_3 \), use the naming rules:- 'P' stands for phosphorus.- 'Cl' stands for chlorine, and with three chlorines, use 'tri-'.Therefore, the compound is named phosphorus trichloride.

Step 4: Name Compound b: \( \text{Cl}_2 \text{O}_7 \)

For \( \text{Cl}_2 \text{O}_7 \), apply:- 'Cl' for chlorine, using 'di-' as the prefix.- 'O' for oxygen, and the prefix 'hepta-' is used for seven oxygens.Thus, the compound is named dichlorine heptoxide.

Step 5: Name Compound c: \( \text{P}_4 \text{O}_6 \)

For \( \text{P}_4 \text{O}_6 \), follow:- 'P' for phosphorus with prefix 'tetra-'.- 'O' for oxygen with prefix 'hexa-'.This results in the name tetraphosphorus hexoxide.

Step 6: Name Compound d: \( \text{NO} \)

For \( \text{NO} \), use:- 'N' stands for nitrogen, no prefix necessary as there is one atom.- 'O' for oxygen with 'mono-' prefixed, forming monoxide.Hence, the compound is called nitrogen monoxide.

Key Concepts

Covalent Compounds Naming

Naming covalent compounds, also known as molecular compounds, involves understanding the structure and composition of the molecules. These compounds form from the sharing of electron pairs between atoms, typically nonmetals. Each atom's role in the molecular structure helps determine the name of the compound.
When naming covalent compounds:

• The first element's name remains unchanged as long as it's a single atom. If there are multiple atoms, prefixes indicate the number.
• The second element's name ends with the suffix 'ide,' and prefixes are used to show how many atoms are present. Prefixes such as 'mono-,' 'di-,' 'tri-,' and so on, let you know the exact count of each element.

Understanding these principles is important to accurately communicate the composition of covalent compounds.

Chemical Formulas

Chemical formulas represent the types and numbers of atoms within a molecule. They provide a clear, shorthand method of understanding a compound's composition.

For example, in the chemical formula \(\text{PCl}_3\), 'P' stands for phosphorus, while 'Cl' stands for chlorine, with a subscript '3' indicating there are three chlorine atoms. Chemical formulas are crucial for identifying the components and ratios within a compound. This system helps both in naming compounds correctly and in predicting their behavior in chemical reactions.

• Subscripts indicate the quantity of each atom.
• Symbols represent elements, using one or two letters.

Correctly interpreting chemical formulas empowers students to name compounds and predict molecular structures effectively.

Molecular Prefixes

Molecular prefixes are essential in the vocabulary of chemistry for accurately naming covalent compounds. They are specifically used to clarify the number of atoms of each element in the compound, ensuring precise communication.

Here are common prefixes you should know:

• 'Mono-': one (often omitted for the first element but used for the second)
• 'Di-': two
• 'Tri-': three
• 'Tetra-': four
• 'Penta-': five
• 'Hexa-': six
• 'Hepta-': seven
• 'Octa-': eight
• 'Nona-': nine
• 'Deca-': ten

Using these prefixes helps remove ambiguity in compound names. For instance, "dichlorine heptoxide" clearly tells us there are two chlorine atoms and seven oxygen atoms.

Naming Rules for Compounds

To accurately name covalent compounds, a systematic approach is necessary. The primary rules ensure consistency and reduce confusion among chemists and students.

Here is a simplified guide to naming:

• The first element's name is written in full. If there are multiple atoms, add the appropriate prefix (e.g., 'dinitrogen' for \(\text{N}_2\)).
• The second element's name has the 'ide' suffix. Apply the proper prefix for the number of atoms (e.g., 'monoxide' for \(\text{O}\)).
• Do not use 'mono-' for the first element's single atom, but do use it for the second.

Let's apply these rules. The name 'phosphorus trichloride' for \(\text{PCl}_3\) consists of 'phosphorus' with no prefix and 'trichloride' indicating three chlorines. Understanding and utilizing these naming rules ensures transparent and accurate communication in chemistry.