Problem 33 - Chemistry for Allied Health

Question

How many atoms of each element are in one unit of each compound? a. \(\mathrm{H}_{2} \mathrm{O}_{2}\) b. \(\mathrm{N}_{2} \mathrm{O}_{5}\) c. \(\mathrm{PF}_{3}\) d. \(\mathrm{MgCl}_{2}\) e. \(\mathrm{KBr}\) f. \(\mathrm{AlCl}_{3}\) g. \(\mathrm{CaO}\) h. \(\mathrm{Na}_{2} \mathrm{~S}\) i. \(\mathrm{NH}_{3}\) j. \(\mathrm{CO}_{2}\) k. \(\mathrm{N}_{2} \mathrm{H}_{4}\) l. \(\mathrm{N}_{2} \mathrm{O}\)

Step-by-Step Solution

Answer

Each compound has different atom counts based on their chemical formulas.

Step 1: Identifying Elements in H₂O₂

The formula for hydrogen peroxide is \( \mathrm{H}_{2} \mathrm{O}_{2} \). It contains hydrogen and oxygen. Count the subscript of each element to find the number of atoms. Hydrogen has a subscript of 2, and oxygen has a subscript of 2.

Step 2: Counting Atoms in N₂O₅

The formula \( \mathrm{N}_{2} \mathrm{O}_{5} \) represents dinitrogen pentoxide. It contains nitrogen and oxygen. The subscript after nitrogen indicates 2 atoms, and there are 5 oxygen atoms.

Step 3: Finding Atoms in PF₃

\( \mathrm{PF}_{3} \) stands for phosphorus trifluoride. This compound includes one phosphorus atom (as there is no subscript indicating more) and three fluorine atoms, indicated by the subscript 3.

Step 4: Determining Atoms in MgCl₂

In \( \mathrm{MgCl}_{2} \), which is magnesium chloride, there is one magnesium atom (no subscript) and two chlorine atoms, as indicated by the subscript 2.

Step 5: Analyzing Atoms in KBr

For \( \mathrm{KBr} \), or potassium bromide, there is one potassium atom and one bromine atom. Neither element has a subscript, indicating one atom each.

Step 6: Counting Atoms in AlCl₃

The formula \( \mathrm{AlCl}_{3} \) indicates one aluminium atom and three chlorine atoms, as shown by the subscript 3.

Step 7: Evaluating Atoms in CaO

The compound \( \mathrm{CaO} \), calcium oxide, includes one calcium atom and one oxygen atom, as neither has a subscript indicating more.

Step 8: Assessing Atoms in Na₂S

In sodium sulfide, \( \mathrm{Na}_{2} \mathrm{S} \), there are two sodium atoms and one sulfur atom (no subscript for sulfur).

Step 9: Identifying Atoms in NH₃

The formula \( \mathrm{NH}_{3} \) represents ammonia, containing one nitrogen atom and three hydrogen atoms indicated by the subscript 3.

Step 10: Determining Atoms in CO₂

For \( \mathrm{CO}_{2} \), carbon dioxide consists of one carbon atom and two oxygen atoms, as shown by the subscript 2.

Step 11: Finding Atoms in N₂H₄

The formula \( \mathrm{N}_{2} \mathrm{H}_{4} \) for hydrazine shows two nitrogen atoms and four hydrogen atoms, as indicated by their respective subscripts.

Step 12: Counting Atoms in N₂O

In \( \mathrm{N}_{2} \mathrm{O} \), dinitrogen monoxide consists of two nitrogen atoms and one oxygen atom (no subscript for oxygen indicating more).

Key Concepts

Subscript in Chemical Formulas

Chemical formulas provide a compact way of indicating the composition of a compound. Understanding subscripts in these formulas is crucial. In a chemical formula, a subscript is the small number written slightly lower and after the chemical symbol of an element. This number tells us how many atoms of that particular element are present in one molecule of the compound. For instance, in the formula for hydrogen peroxide, \( H_2O_2 \), the subscript '2' indicates that there are two hydrogen atoms and two oxygen atoms in each molecule.

• If an element symbol has no subscript, it means there is one atom of that element present in the molecule.
• Subscripts apply only to the element immediately preceding them.
• If a subscript is attached to a molecular group within parentheses, it multiplies the number of each atom inside the group. For instance, \( (OH)_2 \) would mean there are two oxygen and two hydrogen atoms.

It's clear that by looking at the subscripts you can quickly identify the number of each type of atom in a compound. Understanding this basic concept helps in analyzing chemical reactions and compound composition effectively.

Counting Atoms in Compounds

Counting atoms in compounds essentially involves interpreting the subscripts in chemical formulas. It's an important step to understand a compound's structure and predict its chemical behavior. Let's walk through how you can count atoms in several examples:

• For \( N_2O_5 \) (dinitrogen pentoxide), the subscript '2' indicates two nitrogen atoms, while the subscript '5' shows there are five oxygen atoms.
• In \( CO_2 \) (carbon dioxide), the subscript '2' indicates two oxygen atoms, while carbon has no subscript, meaning there is one carbon atom.
• Even without any subscript, atoms can still be counted. In \( KBr \), potassium bromide, both potassium and bromine have no subscripts, so each has only one atom.

Properly counting the atoms helps understand how different elements interact, leading to different properties and reactions. This forms the basis for balancing chemical equations and predicting compound behavior.

Element Identification in Compounds

Identifying elements within a compound is the first step in understanding its composition. Each element in a chemical formula is represented by its chemical symbol, and knowing these symbols allows one to identify what elements are present in a compound.

• In \( PF_3 \) (phosphorus trifluoride), the chemical symbols 'P' and 'F' indicate phosphorus and fluorine are present in the compound.
• For \( MgCl_2 \) (magnesium chloride), 'Mg' stands for magnesium and 'Cl' for chlorine.
• Learning these symbols is essential for analyzing the components of a compound. Different compounds are formed by different combinations and ratios of elements.

Understanding element identification provides insights into the properties of a compound, as each element contributes differently to the compound's overall characteristics. This knowledge is vital in fields ranging from chemistry and pharmacology to materials science and engineering.