Problem 30 - Chemistry and Chemical Reactivity

Question

Give the formula for each of the following compounds: (a) bromine trifluoride (b) xenon difluoride (c) hydrazine (d) diphosphorus tetrafluoride (e) butane

Step-by-Step Solution

Answer

(a) BrF₃, (b) XeF₂, (c) N₂H₄, (d) P₂F₄, (e) C₄H₁₀.

Step 1: Understand the Compound Names and Prefixes

To begin, decipher each compound name. Names often include prefixes indicating the number of atoms, such as 'mono-' for 1, 'di-' for 2, 'tri-' for 3, 'tetra-' for 4, etc. Understanding these prefixes will guide the formulation.

Step 2: Write the Formula for Bromine Trifluoride

'Bromine trifluoride' consists of one bromine atom and three fluorine atoms. The prefix 'tri-' denotes three fluorine atoms. Thus, the formula is \( \text{BrF}_3 \).

Step 3: Write the Formula for Xenon Difluoride

Xenon difluoride contains one xenon atom and two fluorine atoms, as indicated by the prefix 'di-'. Therefore, the formula is \( \text{XeF}_2 \).

Step 4: Write the Formula for Hydrazine

Hydrazine is a common name that doesn't use prefixes. It is a nitrogen-hydrogen compound with the formula \( \text{N}_2\text{H}_4 \). Memorize common names like this.

Step 5: Write the Formula for Diphosphorus Tetrafluoride

The name 'diphosphorus tetrafluoride' indicates two phosphorus atoms ('di-') and four fluorine atoms ('tetra-'). Therefore, the chemical formula is \( \text{P}_2\text{F}_4 \).

Step 6: Write the Formula for Butane

Butane is an alkane with four carbon atoms and ten hydrogen atoms. The general formula for alkanes is \( \text{C}_n\text{H}_{2n+2} \). For butane, \( n = 4 \), so the formula is \( \text{C}_4\text{H}_{10} \).

Key Concepts

Compound Names

Compound names in chemistry give us essential information about the atoms present in a molecule and sometimes their arrangement. The name of a compound reflects its chemical structure and composition. Compound names are typically derived from rules laid out by the International Union of Pure and Applied Chemistry (IUPAC).

Names are constructed by combining the names of the elements involved, often using Greek or Latin roots. For example:

• Bromine trifluoride indicates the presence of bromine with three fluorine atoms.
• Xenon difluoride suggests xenon with two fluorine atoms.

Memorizing common compounds like hydrazine can also be useful. Hydrazine doesn't follow the usual naming conventions. Instead, it is recognized by its habitual name. Understanding compound names is the first step in determining molecular compositions.

Prefixes in Chemistry

Prefixes in chemistry provide information about the number of specific atoms within a compound. These prefixes are borrowed from Greek, and they play a crucial role in the nomenclature of molecules. For the compounds given:

• 'Mono-' indicates one atom (though often omitted for the first element).
• 'Di-' stands for two, as seen in xenon difluoride ( \( ext{XeF}_2\)).
• 'Tri-' represents three, present in bromine trifluoride ( \( ext{BrF}_3\)).
• 'Tetra-' indicates four, such as in diphosphorus tetrafluoride ( \( ext{P}_2 ext{F}_4\)).

These prefixes help strip away the complexity of chemical formulation. Once mastered, the task of writing chemical formulas becomes much more straightforward.

Molecular Composition

Molecular composition refers to the specific arrangement and quantity of atoms in a molecule. Determining this involves recognizing the elements in a compound and how many of each are present. Given the compounds:

• Bromine trifluoride consists of one bromine and three fluorine atoms: \( ext{BrF}_3\).
• Xenon difluoride is composed of one xenon and two fluorine atoms: \( ext{XeF}_2\).
• Hydrazine contains two nitrogen and four hydrogen atoms, with \( ext{N}_2 ext{H}_4\) as its formula.
• Diphosphorus tetrafluoride consists of two phosphorus atoms and four fluorine atoms: \( ext{P}_2 ext{F}_4\).
• Butane, an alkane, has four carbons and ten hydrogens, represented by \( ext{C}_4 ext{H}_{10}\).

This highlights the significance of accurately interpreting molecular composition to understand chemical behavior and properties.

Alkanes

Alkanes are a group of hydrocarbons consisting entirely of carbon (C) and hydrogen (H) atoms. They are saturated, meaning each carbon atom makes four single covalent bonds, fulfilling the "octet rule" by sharing pairs of electrons.

The generic formula for alkanes is \( ext{C}_n ext{H}_{2n+2}\), where \(n\) represents the number of carbon atoms. This formula allows us to easily evaluate molecular composition:

• For butane, with \(n = 4\), substituting gives \( ext{C}_4 ext{H}_{10}\).

Alkanes are typically used as fuels due to their combustible nature. They play an important part in everyday life, existing in different forms such as methane, propane, and more. Understanding alkanes will greatly benefit students, as they constitute a fundamental aspect of organic chemistry. By mastering the use of formulas, students can quickly identify these molecules and predict their behavior in chemical reactions.