Question

Which of these formulas represent molecules? State how many atoms are in each molecule. a) \(\mathrm{Fe}\) b) \(\mathrm{PCl}_{3}\) c) \(\mathrm{P}_{4}\) d) \(\mathrm{Ar}\)

Short answer

b) \(\mathrm{PCl}_3\) (4 atoms), c) \(\mathrm{P}_4\) (4 atoms) are molecules.

Step-by-step solution

Understanding Chemical Formulas

Chemical formulas represent molecules when they consist of two or more atoms bonded together. Each distinct letter in the formula represents a different element, with the subscript number indicating the number of atoms for that element.

Evaluation of Molecule a: \(\mathrm{Fe}\)

The formula \(\mathrm{Fe}\) consists of a single element without any subscript. This indicates that it is a single atom of iron, not a molecule. Molecules must consist of more than one atom.

Evaluation of Molecule b: \(\mathrm{PCl}_3\)

The formula \(\mathrm{PCl}_3\) includes phosphorus (P) and chlorine (Cl) with a subscript of 3 for Cl, indicating three chlorine atoms. This represents a molecule consisting of 1 phosphorus atom and 3 chlorine atoms, totaling 4 atoms.

Evaluation of Molecule c: \(\mathrm{P}_4\)

The formula \(\mathrm{P}_4\) indicates four atoms of phosphorus. Even though it consists of only one element, multiple atoms qualify it as a molecule. There are 4 atoms in total.

Evaluation of Molecule d: \(\mathrm{Ar}\)

The formula \(\mathrm{Ar}\) refers to a single argon atom. Argon is a noble gas typically found as individual atoms rather than in molecules. Thus, \(\mathrm{Ar}\) is not a molecule.

Final Assessment

From the analysis, \(\mathrm{PCl}_3\) and \(\mathrm{P}_4\) are molecules. \(\mathrm{Fe}\) and \(\mathrm{Ar}\) are individual atoms, not molecules.

Key concepts

Chemical Formulas

Chemical formulas are shorthand representations used to describe the composition of molecules in chemistry. They indicate the elements involved and the number of atoms of each element in a single molecule. For example, in the formula \(\mathrm{PCl}_3\), 'P' stands for phosphorus and 'Cl' for chlorine. The subscript '3' next to Cl denotes that there are three chlorine atoms bonded with one phosphorus atom.

These formulas help chemists and students understand the structure and makeup of chemical compounds quickly. If no subscript is present, it implies there is only one atom of that element in the molecule. Understanding chemical formulas allows for the prediction of chemical behavior and reactions.

Atoms

Atoms are the fundamental building blocks of matter. They are the smallest units of an element that retain all the properties of that element. For example, an iron atom (\(\mathrm{Fe}\)) represents the smallest unit of iron that still maintains the characteristics of iron itself.

An atom consists of a nucleus containing protons and neutrons, with electrons orbiting around this nucleus. In chemical reactions, atoms can gain, lose, or share electrons, leading to the formation of chemical bonds and the creation of molecules. Therefore, atoms are crucial in forming chemical compounds and understanding their interactions.

Element Classification

Elements are classified based on their properties and position on the periodic table. Each element, such as iron \(\mathrm{Fe}\) or argon \(\mathrm{Ar}\), is composed of only one type of atom. Elements can be metals, non-metals, or metalloids, each with distinct physical and chemical characteristics.

Classification helps in predicting an element's reactivity and its ability to form compounds. For instance, argon is a noble gas, well-known for its lack of reactivity and tendency to exist as isolated atoms, rather than forming molecules. Similarly, iron, a metal, is typically malleable and conductive. Understanding the classification of elements aids in discerning their roles in chemical reactions and natural processes.