Question

Simple Lewis Structures, Formulas, and Names fo Write a formula for each molecular compound. \begin{equation} \begin{array}{l}{\text { a. phosphorus trichloride }} \\ {\text { b. chlorine monoxide }} \\ {\text { c. disulfur tetrafluoride }} \\ {\text { d. phosphorus pentafluoride }}\end{array} \end{equation}

Short answer

\[ \text{a. } PCl_3, \text{ b. } ClO, \text{ c. } S_2F_4, \text{ d. } PF_5 \]

Step-by-step solution

Interpret a.

Phosphorus trichloride means that there is one phosphorus atom and three chlorine atoms. The prefix 'tri-' indicates three chlorines.

Write the Formula for a.

The chemical symbol for phosphorus is P and for chlorine is Cl. Since there are three chlorine atoms, the formula is written as \( PCl_3 \).

Interpret b.

Chlorine monoxide means there is one chlorine atom and one oxygen atom. The prefix 'mono-' indicates a single atom, which is typically not used for the first element but is used here for clarity.

Write the Formula for b.

The chemical symbol for chlorine is Cl and for oxygen is O. The formula is written as \( ClO \).

Interpret c.

Disulfur tetrafluoride indicates there are two sulfur atoms and four fluorine atoms. The prefix 'di-' means two for sulfur and 'tetra-' indicates four for fluorine.

Write the Formula for c.

The chemical symbol for sulfur is S and for fluorine is F. The formula is written as \( S_2F_4 \).

Interpret d.

Phosphorus pentafluoride means there is one phosphorus atom and five fluorine atoms. The prefix 'penta-' indicates five.

Write the Formula for d.

The chemical symbol for phosphorus is P and for fluorine is F. The formula is written as \( PF_5 \).

Key concepts

Understanding Lewis Structures

Lewis structures, also known as Lewis dot diagrams, are a visual representation of the bonding between atoms of a molecule and the lone pairs of electrons that may exist. To understand and draw these structures, you need to know the valence electrons for each atom, which can be found by looking at the group number in the periodic table. For example, in the exercise, phosphorus (P) has five valence electrons and chlorine (Cl) has seven.

When drawing a Lewis structure, start by arranging the atoms to show which are bonded together, then distribute the valence electrons around each atom, starting with the bonded pairs. Remember, the main goal is to have each atom achieve a stable octet, or duet for hydrogen, reminiscent of a noble gas configuration. In the exercise given, the compound phosphorus trichloride (PCl₃) would be depicted as a phosphorus atom with three chlorines bonded to it, each chlorine with three lone pairs to complete its octet and phosphorus with an additional lone pair.

Molecular Compound Naming Basics

Naming molecular compounds involves recognizing the number of atoms present and using appropriate prefixes to reflect those quantities. The prefixes are 'mono-' for one, 'di-' for two, 'tri-' for three, all the way up to 'deca-' for ten. In practice, we don't typically use 'mono-' for the first element if there's only one atom of it – it's understood.

Let's take chlorine monoxide as an example. It consists of one chlorine and one oxygen atom. According to the standard naming convention, we would call it chlorine monoxide, even though we could skip the 'mono-' prefix because there's just one oxygen atom. For compounds with two different non-metal elements, like the examples in the exercise, we use these prefixes to indicate the number of each type of atom in the molecule, leading to names like disulfur tetrafluoride (S₂F₄).

Chemical Nomenclature Explained

Chemical nomenclature is the systematic process of naming chemicals to ensure clear communication among scientists. For binary compounds, which contain only two different elements like those in the given exercise, the name starts with the prefix indicating the number of atoms of the first element (except 'mono-'), followed by the base name of this element. The second part of the compound's name begins with a prefix for the number of atoms of the second element and ends with the suffix '-ide'.

To illustrate, for phosphorus pentafluoride, the 'penta-' prefix tells us there are five fluorine atoms bonded to a single phosphorus atom. We use the suffix '-ide' to indicate that fluorine, the more electronegative element, is in a compound with another non-metal. In each case, whether writing formulas or naming compounds, it is critical to use these nomenclature rules accurately to avoid misunderstandings and ensure the correct chemical is described or produced.