Question

Which elements have molecules as their basic units? (a) helium (b) oxygen (c) iron (d) bromine

Short answer

Oxygen (O) and bromine (Br) have molecules as their basic units.

Step-by-step solution

Understanding Molecular Elements

Elements that have molecules as their basic units are those where two or more atoms of the same element bond together. These molecules are diatomic, meaning they consist of two atoms.

Identifying Diatomic Elements

From the given options, identify which elements naturally exist as diatomic molecules at standard temperature and pressure. The seven diatomic elements that are most commonly taught are hydrogen (H), nitrogen (N), oxygen (O), fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).

Evaluating Each Option

Compare each option with the list of diatomic elements:(a) Helium is a noble gas and exists as single atoms, not molecules.(b) Oxygen is a diatomic element and exists as molecules (O2).(c) Iron is a metal and exists as atoms arranged in a crystal lattice, not as molecules.(d) Bromine is a diatomic element and exists as molecules (Br2).

Selecting the Correct Elements

The elements from the provided options that have molecules as their basic units are oxygen (O) and bromine (Br).

Key concepts

Molecular Elements

Molecular elements, also often referred to as diatomic elements, are a specific type of element that exist naturally as molecules rather than single atoms. These molecules consist of two atoms that are chemically bonded together. While many elements can form molecular compounds, there are only a few elements that are molecular in their most stable form. This includes seven elements that are quintessentially known as diatomic under standard environmental conditions: hydrogen (H₂), nitrogen (N₂), oxygen (O₂), fluorine (F₂), chlorine (Cl₂), bromine (Br₂), and iodine (I₂).

Understanding this concept can vastly improve a student's ability to solve problems related to elemental states. When considering the form in which these elements exist, one should remember that they prefer to 'pair up' to achieve a more stable state. This behavior is dictated by the principles of atomic stability and quantum mechanics.

Key Characteristics of Diatomic Elements

• They are made up of two atoms.
• Have a strong chemical bond between the atoms forming a molecule.
• They are gases or liquids at room temperature, with the exception of iodine, which is a solid.
• Exist in their elemental form under standard temperature and pressure conditions.

These characteristics make diatomic molecules distinct and highly relevant for both academic studies and practical applications in chemistry.

Standard Temperature and Pressure

Standard temperature and pressure (STP) are set of conditions for the measurement of gases that allows scientists and engineers to compare different sets of experimental data without the interference from varying temperatures and pressures. STP is commonly defined as a temperature of 0°C (273.15 K) and a pressure of 1 atmosphere (atm) or 101.325 kilopascals (kPa).

At STP, the behavior of gases, including molecular elements, becomes more predictable and follows the gas laws more closely, thereby simplifying calculations and theoretical predictions. For instance, under STP, one mole of any ideal gas occupies 22.414 liters of volume.

Importance of STP in Chemistry

• Allows for the comparison and replication of experimental results.
• STP conditions are used to define the standard molar volume of a gas.
• Essential for predicting the behavior of gases using the ideal gas law.
• It's the baseline for tabulated values of enthalpy, entropy, and other thermodynamic properties.

Appreciating the role of STP in chemistry will not only ease the understanding of gaseous behaviors but also underpin many principles in chemical thermodynamics and kinetics.

Noble Gases

Noble gases make up a small but significant group in the periodic table, known for their remarkable lack of chemical reactivity. This inertness is due to their completely filled valence electron shells, which make these gases highly stable and seldom part of chemical reactions under normal conditions. The noble gases include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and the radioactive radon (Rn).

While the diatomic elements bond with themselves to achieve stability, noble gases intrinsically possess it. As such, they do not form molecules under standard conditions and are always found as monatomic gases, meaning each gas is composed of single atoms. This unique property sets them apart from the molecular elements, which need to form diatomic or polyatomic molecules to stabilize themselves.

Unique Features of Noble Gases

• Complete electron shells leading to chemical inertness.
• Exist as single atoms, not bonded to others.
• Colorless, odorless, and tasteless in their natural state.
• Used in lighting, welding, and space exploration because they do not react with other materials.

Knowledge of noble gases and their unique characteristics is important when discussing chemical stability, reactivity, and the overall organization of the periodic table.