Question

What are the basic units single atoms, molecules, or formula units-that compose each substance? (a) \(\mathrm{BaBr}_{2}\) (b) Ne (c) \(\mathrm{I}_{2}\) (d) \(\mathrm{CO}\)

Short answer

The basic units are: (a) formula units for BaBr2, (b) single atoms for Ne, (c) molecules for I2, (d) molecules for CO.

Step-by-step solution

Identify the Substance Type

To determine the basic units, we need to identify whether each given substance is an element or a compound. Elements are composed of single atoms, while compounds are composed of molecules or formula units.

Classify Each Substance

Classify each of the substances given as either an element or a compound. This step involves recalling or researching the periodic table and basic chemical knowledge.

Determine the Basic Units for Each Substance

For each classified substance, assign the corresponding basic unit. For elements, the basic unit is a single atom, while for compounds, it can be a molecule or a formula unit depending on if the compound is molecular or ionic.

Key concepts

Elements and Compounds

Understanding the distinction between elements and compounds is a foundational aspect of chemistry.

An element is a pure substance composed of only one type of atom. Examples of elements include hydrogen, oxygen, and neon. Elements cannot be broken down into simpler substances by chemical means. On the periodic table, each element is represented by a unique symbol, such as H for hydrogen or O for oxygen.

Compounds, on the other hand, are substances formed when two or more different elements combine in fixed ratios. Compounds possess different properties than the elements that make them up. For instance, water (H₂O) is a compound made of hydrogen and oxygen, and it has unique properties distinct from both gases.

Understanding these differences is crucial when identifying the basic units of substances. Elements exist as single atoms, while compounds are made up of molecules or formula units, depending on their bond types. For example, BaBr₂ is a compound composed of barium and bromine atoms in a ratio that forms formula units due to its ionic nature.

Periodic Table

The periodic table is an organized chart of all known elements arranged by increasing atomic number—that is, the number of protons in an atom's nucleus.

The periodic table is an essential tool in chemistry as it provides valuable information about the elements' properties and how they interact with each other. Elements are grouped into rows called periods and columns called families or groups which share similar characteristics. For example, the noble gases like neon (Ne) in group 18 are known for being inert because they rarely form compounds due to their full valence electron shells.

By using the periodic table, scientists can predict the behavior of elements, how they bond, and whether they will form compounds. It serves not only as a reference for classification but also as a predictive tool for chemical reactions and the formation of different substances.

Molecules and Formula Units

The concept of molecules and formula units is integral in describing the composition of compounds.

A molecule is the smallest unit of a compound that can exist while retaining the chemical properties of the compound. Molecules are composed of atoms covalently bonded together, such as the oxygen molecules (O₂) we breathe or the carbon monoxide (CO) molecule, which is a toxic gas. These molecules consist of non-metal elements sharing electrons to form stable configurations.

Concept of a Molecular Compound

A molecular compound, for example I₂, is composed of molecules wherein atoms are held together by covalent bonds.

Formula units, however, refer to the simplest ratio of ions represented in an ionic compound, which exists due to the electrostatic attraction between oppositely charged ions. For example, BaBr₂ contains one barium ion and two bromide ions in its formula unit. Unlike covalently bonded molecules, ionic compounds form crystalline structures that extend in a lattice rather than discrete molecules.

Grasping the concept of molecules and formula units is essential when analyzing substances and their chemical makeup.