7.2. Molecular Compounds http://www.ck12.org
7.2 Molecular Compounds
Lesson Objectives
- Define a molecule and give examples of molecules.
- Be able to name a molecular compound when given its formula.
- Be able to write the formula for a molecular compound when given its name.
- Know the common names for some simple molecular compounds, such as methane (CH 4 ), ammonia (NH 3 ),
phosphine (PH 3 ), water (H 2 O), and hydrogen sulfide (H 2 S).
Lesson Vocabulary
- covalent bond: Two or more atoms bonded together by sharing electrons.
- molecule: A group of atoms are joined together by covalent bonds.
- molecular formula: Designates how many of each atom are in a single molecule of that substance.
- binary molecular compound: A molecular compound that is composed of two elements.
Check Your Understanding
- Give an example of a cation and an anion.
- Give an example of an ionic compound.
- Name the following compounds: MgO, CuO.
Introduction
So far we have looked at ionic compounds, in which atoms of various elements gain or lose electrons to produce
ions. The resulting ions are held together by strong attractions between oppositely charged particles. However, this
only works for bonds between atoms in which one partner (the metal) has a tendency to lose electrons, and the other
(the nonmetal) has a tendency to gain them. Then how might two nonmetals, such as nitrogen and oxygen, form
chemical bonds? Neither is likely to lose electrons and become a cation, but both require more electrons to reach
a noble gas configuration. Instead of a complete transfer of electrons, these atoms can bond by sharing electrons,
producing what is called acovalent bond. When a group of atoms are joined together by covalent bonds, the
resulting structure is called amolecule. Molecules are generally much smaller than the extended three-dimensional
networks of ions that are seen in ionic compounds. We will look much more at covalent bonding and molecules in
future chapters, but for now, we will focus on the ways in which molecules are named.