Periodic Table Groups and Chemical Bonding Fundamentals

Posted on Oct 8, 2025 in Chemistry

Periodic Table Groups and Electron Configuration

Main Groups of the Periodic Table

The elements are categorized into groups based on their chemical properties:

  • Group 1: Alkali Metals (Tend to increase density and decrease the melting and boiling points down the group.)
  • Group 2: Alkaline Earth Metals
  • Group 13: Boron Group (Boroideos)
  • Group 14: Carbon Group (Carbonoideos)
  • Group 15: Nitrogen Group (Nitrogenoideos)
  • Group 16: Chalcogens
  • Group 17: Halogens (Density, boiling points, and melting points increase with the atomic number.)
  • Group 18: Noble Gases (At room temperature, they are monatomic gases and have no tendency to combine with other atoms to form compounds.)

Orbital Capacity and Filling Order

The maximum number of electrons that can occupy each orbital type is:

  • S orbital: 2 electrons
  • P orbital: 6 electrons
  • D orbital: 10 electrons
  • F orbital: 14 electrons

Simplified Orbital Filling Sequence (Aufbau Principle)

1S
2S 2P
3S 3P 3D
4S 4P 4D 4F
5S 5P 5D 5F
6S 6P
7S

Ions and Periodic Trends

Ion Formation

  • A cation is formed when an atom loses one or more electrons.
  • An anion is formed when an atom gains one or more electrons.

Atomic Radius

The volume of the atom is determined by the volume of the electron cloud, which varies in the same way as the atomic radius:

  • Within a period (left to right): The atomic radius decreases as the atomic number grows.
  • Within a group (top to bottom): The atomic radius increases as the atomic number grows.

Ionic Radius

When an atom is ionized, its volume changes:

  • If an atom loses electrons, it becomes a cation and its radius decreases.
  • If an atom gains electrons, it becomes an anion and its radius increases.

Metallic Character

Metallic character is determined by the tendency of an atom to lose electrons:

  • The fewer valence electrons an element has, the higher the metallic character.
  • The larger the atom, the higher its metallic character.

Chemical Bonding

A chemical bond is the union of atoms in a molecule or crystal, formed through the force of attraction between them. Bonds may form:

  • Discrete Molecules: Isolated groups of atoms.
  • Crystal Lattices: Continuous structures.

The Octet Rule

Atoms of different chemical elements tend to bind to other atoms to achieve 8 electrons in their outermost layer (the octet), thereby achieving greater stability.

Types of Chemical Bonds

1. Ionic Bond

The ionic bond is the union of oppositely charged ions by electrostatic attraction forces. This type of bonding occurs between a metal (which yields electrons, becoming a cation) and a nonmetal (which gains electrons, becoming an anion).

Ionic substances form a giant, three-dimensional continuous structure called an ionic crystal. An ionic compound is represented symbolically by an empirical formula, which indicates the proportion of each class of ions in the crystal, conditioned by the principle of charge neutrality.

Properties of Ionic Substances:

  • They are solid at room temperature and melt at high temperatures.
  • They are hard but brittle.
  • Solubility in water is variable. If soluble, they dissolve into ions, making their solutions electrically conductive (electrolytes).
  • They do not conduct electricity in the solid state, but they do when melted or in solution.

2. Covalent Bond

The covalent bond takes place between nonmetals. Since both atoms need to gain electrons to achieve stability, they bind by sharing electrons.

A. Molecular Covalent Substances

These substances consist of molecules bound together by very weak intermolecular forces.

  • Low melting and boiling points.
  • Low density in the solid state.
  • Soluble in water and other solvents.
  • Not electrical conductors.

B. Atomic Covalent Substances (Covalent Networks)

Their atoms are united by covalent bonds but do not form discrete molecules. They form a continuous structure where atoms are linked by very strong covalent bonds.

  • They are dense and very hard solids.
  • They are insoluble in any solvent.
  • They do not conduct electricity.

3. Metallic Bond

The metallic bond occurs between atoms of metal elements. The atoms acquire a positive charge by ejecting electrons into a ‘sea’ of delocalized electrons.

Properties of Metallic Substances:

  • Metallic luster.
  • Dense solids or liquids.
  • They can be drawn into wire (ductile) or hammered into foil (malleable).
  • They are insoluble.
  • They are good electrical and thermal conductors.

Alloys are solutions in which one or more metals are dissolved in a primary metal.