Question

Which of these formulas represent molecules? State how many atoms are in each molecule. a) \(I_{2}\) b) He c) \(\mathrm{H}_{2} \mathrm{O}\) d) \(\mathrm{Al}\)

Short answer

I2 and H2O are molecules; I2 has 2 atoms, and H2O has 3 atoms.

Step-by-step solution

Identify Molecule Formulas

To determine which formulas represent molecules, we need to understand that a molecule is typically composed of two or more atoms bonded together. Individual elements like 'He' or 'Al' are not considered molecules unless they form a compound.

Analyze Each Formula

Examine each formula given: - **(a)** \( I_2 \): Represents a molecule because it consists of two iodine atoms bonded together.- **(b)** \( He \): Does not represent a molecule; it is a noble gas atom.- **(c)** \( \mathrm{H}_2\mathrm{O} \): Represents a molecule consisting of two hydrogen atoms and one oxygen atom.- **(d)** \( Al \): Does not represent a molecule; it is a single aluminum atom.

Count the Atoms in Each Molecule

Count the number of atoms in each formula that is identified as a molecule:- **(a)** \( I_2 \): Has 2 iodine atoms.- **(c)** \( \mathrm{H}_2\mathrm{O} \): Has 2 hydrogen atoms and 1 oxygen atom, totaling 3 atoms.

Key concepts

Atomic Structure

Atomic structure forms the foundation for understanding how molecules are composed. Atoms consist of three main particles: protons, neutrons, and electrons.
The protons and neutrons reside in the nucleus, while electrons orbit around it.
The number of protons in the nucleus determines the element's atomic number.Each element has a unique atomic structure. For instance, helium (He) has an atomic number of 2, indicating two protons and typically two electrons in a neutral atom.
This balanced number of protons and electrons makes helium neutral and stable. Similarly, the atomic structure of iodine (I) consists of 53 protons and electrons in a neutral state.

• Protons: Positively charged particles in the nucleus.
• Neutrons: Neutral particles also found in the nucleus.
• Electrons: Negatively charged particles orbiting the nucleus.

Understanding atomic structure is crucial for analyzing molecular structures like those in the exercise, as it helps to determine how atoms interact and bond to form molecules like iodine \( I_2 \) and water \( \mathrm{H}_2\mathrm{O} \).

Chemical Formulas

Chemical formulas provide a shorthand way of conveying the types and numbers of atoms in a molecule. They help indicate what elements are present in a compound and in what proportion.
For example, the chemical formula \( \mathrm{H}_2\mathrm{O} \) signifies a molecule of water composed of two hydrogen atoms and one oxygen atom.
Chemical formulas are important because they provide insight into the molecular composition of substances. When it comes to molecular representation, formulas like \( I_2 \) tell us that the molecule consists of two iodine atoms bonded together, whereas He is merely a symbol for the element helium with no bonds.

• Subscripts indicate the number of each type of atom in the molecule.
• Letters (e.g., H, O, I) represent the elements involved.
• Molecules possess distinct chemical formulas if they include two or more atoms.

By reading a chemical formula, one can predict how compounds might react chemically, ensuring a distinct understanding of substances like \( \mathrm{H}_2\mathrm{O} \) versus lone elements like He or Al.

Bonding

Bonding refers to the forces that hold atoms together within a molecule. When atoms bond, they either share or transfer electrons, creating a stable structure.
There are various types of chemical bonds: covalent, ionic, and metallic, which are the most common.

Covalent Bonds

In covalent bonds, atoms share pairs of electrons to fill their outer shells, achieving stability. This type of bond is exemplified in molecules like water \( \mathrm{H}_2\mathrm{O} \), where hydrogen and oxygen share electrons.

Ionic Bonds

Ionic bonds form when electrons are transferred from one atom to another, resulting in positive and negative ions that attract each other. However, in the solutions of the original exercise, ionic bonds are not featured since the discussed molecules like \( I_2 \) use covalent bonding.

• Covalent bonding involves sharing electrons.
• Stable molecules achieve electron configuration resembling noble gases.
• The more electrons shared or transferred, the stronger the bond.

Understanding bonding principles aids in visualizing how atoms join to form molecules, determining their structure, and anticipating their properties and reactions. This knowledge is pivotal, especially in determining whether a formula like \( I_2 \) represents a molecular bond while distinguishing single atoms like Al.