Introduction
This chapter connects atomic structure (Chapter 1) to the observable chemical behaviour of elements, organised by their position in the periodic table — the single most useful organising framework in all of chemistry.
1. Periodic classification and trends
Elements are arranged by increasing atomic number into periods (rows, representing successive electron shells) and groups (columns, sharing similar valence electron configurations and therefore similar chemical behaviour). Trends already introduced in Chapter 1 — atomic radius, ionization energy, electronegativity — together explain broader patterns: metallic character decreases across a period (elements more readily attract rather than lose electrons) and increases down a group.
2. Ionic, covalent, and coordinate bonding
Ionic bonding results from electron transfer between atoms of very different electronegativity, producing oppositely charged ions held together by electrostatic attraction (typically metal + nonmetal). Covalent bonding results from electron sharing between atoms of similar electronegativity (typically nonmetal + nonmetal), and can be polar (unequal sharing) or nonpolar (equal sharing). Coordinate (dative) bonding is a covalent bond where both shared electrons originate from a single atom (a Lewis base donating a lone pair to a Lewis acid) — central to complex ion formation, developed fully in Chapter 9.
3. Acid–base and redox behaviour in inorganic systems
Many inorganic reactions are classifiable as acid–base (proton or electron-pair transfer, developed fully in Chapter 9) or redox (electron transfer, as in Chapter 2) — recognising which type of reaction is occurring is the first step in predicting or balancing it correctly.
4. Representative-element chemistry
Beyond general trends, each group of representative (main-group) elements has characteristic chemistry worth knowing at a working level: alkali metals (Group 1) are highly reactive, forming +1 ions readily; alkaline earth metals (Group 2) form +2 ions and are somewhat less reactive; halogens (Group 17) are highly reactive nonmetals forming −1 ions or covalent compounds; noble gases (Group 18) are largely unreactive due to their complete valence shells. These patterns are direct consequences of how easily each group’s atoms can achieve a stable, complete valence configuration.
5. Structure–property relationships
The type of bonding and structure in a compound directly determines its bulk properties: ionic compounds tend to have high melting points and conduct electricity when molten or dissolved (mobile ions); covalent molecular compounds tend to have lower melting points and do not conduct (no mobile charge carriers); covalent network solids (like diamond) can have extremely high melting points because breaking the structure means breaking covalent bonds throughout the entire lattice, not just overcoming weak intermolecular forces.
Key Takeaways
- The periodic table organises elements by shared valence electron configuration, from which broader trends (metallic character, reactivity patterns) follow.
- Ionic (electron transfer), covalent (electron sharing), and coordinate (one-sided electron donation) bonding are distinguished by how bonding electrons originate and are shared.
- Representative-element group chemistry follows directly from each group’s characteristic path to a stable valence configuration.
- Bulk physical properties (melting point, conductivity) are direct, explainable consequences of a compound’s bonding type and structure.