Which of the following statements is/are always true? Never true? Usually true? (a) Compounds containing carbon atoms are molecular. (b) A molecule is made up of nonmetal atoms. (c) An ionic compound has at least one metal atom.

Understanding chemical bonding is essential for grasping how atoms join together to form compounds. At its core, chemical bonding involves the attraction between atoms that allows the formation of chemical substances containing two or more atoms. The bond is a result of the electrostatic forces between opposite charges, be they ionic bonds formed between metals and nonmetals, or covalent bonds that occur when nonmetals share electrons.

Chemical bonds dictate the chemical and physical properties of substances. Stronger bonds, such as those found in ionic compounds, typically result in higher melting and boiling points. In contrast, molecular compounds, which are usually bound by covalent bonds, commonly have lower melting and boiling points due to the weaker intermolecular forces at play. The concept of chemical bonding is not just limited to two categories; it includes metallic bonding and hydrogen bonding among others. However, for the purpose of this problem analysis, we focus on ionic and covalent bonds, which define the structure of ionic and molecular compounds respectively.

Molecular compounds are types of chemicals where the atoms share electrons via covalent bonds. These bonds are pivotal for the stability of the molecules formed by nonmetals. The shared electrons allow each atom to achieve a full outer shell of electrons, achieving a more stable electronic configuration. One common misconception is that all carbon-containing compounds are molecular; while many organic compounds are molecular, carbon can also form ionic compounds such as carbonates and cyanides.

Molecular compounds often have distinct characteristics, including lower melting and boiling points compared to ionic compounds, which means many are gases or liquids at room temperature. They do not conduct electricity in their solid state or when dissolved in water, as they do not have charged particles free to move and carry an electric current. The detailed examination of this type of compound helps explain why the statement about molecules being made up of nonmetal atoms is considered 'usually true' instead of an absolute.

Ionic compounds are chemical substances defined by the presence of an ionic bond, which involves the transfer of electrons from a metal atom to a nonmetal atom. This transfer creates ions: the metal becomes a positively charged cation and the nonmetal becomes a negatively charged anion. These ions are held together in a lattice structure by strong electrostatic forces, giving ionic compounds their distinctive high melting and boiling points.

Additionally, ionic compounds typically conduct electricity when dissolved in water or melted, due to the movement of free ions. A crucial point to take away from the problem analysis is the 'always true' statement that an ionic compound contains at least one metal atom. This is a key aspect in the identification and classification of compounds in chemistry. Notably, these fundamental properties of ionic compounds are used extensively in industry, medicine, and technology—for instance, in the manufacture of salts like sodium chloride.