・2110　Valence electrons and core electrons
　Among the electrons in atoms, there are those that are involved in chemical bonds and those that are not. Topics: valence electrons, valence orbitals, core electrons, core atomic orbitals

・2120　Atomic electron configuration and chemical bonds　
　Explains the octet rule of chemical bonding and changes in electron configuration in chemical bonds. Topics: free energy, chemical bond, octet side, ionization energy, octet, lone electrons, Lewis structure, bond electron pairs, promotion

・2130　Bonding electron pairs and non-bonding electron pairs
　Some atoms have non-bonding electron pairs. Explain why. Topics: non-bonding electron pairs, unshared electron pairs, lone electron pairs

・2140　Chemical bonds involving non-bonding electron pairs (coordinate bonds)
　Non-bonding electron pairs also form chemical bonds. This is called a coordinate bond. Topics: Non-bonding electron pairs, coordinate bonds

・2150　Valence
　Explain atomic valence and related terms. Topics: atomic valence, primary valence, side valence, coordinate bond

・2160　Types of Chemical Bonds
　Chemical bonds are classified into four types based on the bonding method and the electronegativity of the atoms. Topics: Covalent bond, Coordinate bond, Metallic bond, Ionic bond, Coulomb force, Electronegativity

・2170　Electronegativity
　Atoms have different strengths in attracting electrons, which is called electronegativity. We will investigate the causes of electronegativity and its effect on chemical bonds. Topics: Electronegativity, bond energy, valence electrons, polarization

・2180　Ionic bond
　Among the chemical bonds classified in 2160, we will explain ionic bonds. Topics: electronegativity, Coulomb force, crystals of inorganic compounds, molecular bonding in the gaseous state

・2190　Metallic bond
　Clarify the origin of metallic bonds that give metals their characteristics. Topics: Metallic elements, nonmetallic elements, electronegativity, uncertainty principle, ionization energy, metallic hydrogen

・2200　Covalent bond
　This section provides an overview of typical covalent bonds in organic compounds. For more details, see 2210. Topics: electronegativity, polarization, ionic bonding