Chemical Bonding & Periodic Table Essentials

Posted on Nov 20, 2024 in Chemistry

Molecular Union & Crystal Structure

Molecular union of atoms results in discrete groups. Network crystals have millions of atoms ordered regularly. Chemical linkage is the force of attraction holding atoms in a molecule or crystal, known as chemical bonds.

Octet Rule

Atoms of different chemical elements tend to unite to achieve stability by having eight electrons in their last layer, called the octet.

Ions

Cation: Metallic element losing electrons, positively charged.
Anion: Non-metallic element gaining electrons, negatively charged.

Ionic Bond

Union of oppositely charged ions due to electrostatic attraction. Properties of ionic substances:

  • Solid at room temperature, high melting points.
  • Hard but fragile due to the arrangement of ions.
  • Variable solubility in water (electrolytes).
  • Do not conduct electricity in solid state, but do in molten or solution state.

Covalent Bond

Union of atoms sharing electrons. Properties of molecular substances:

  • Low melting and boiling points, often gases or volatile liquids/solids.
  • Low density, soft, and less resistant.
  • Soluble in water or other solvents like acetone or gasoline.
  • Non-conductors of electricity due to shared electrons.

Atomic Substances

  • Solid, dense, and hard.
  • Insoluble.
  • Do not conduct electricity (except graphite).

Metallic Link

Occurs between metallic elements where atoms expel electrons, creating a cohesive structure due to the electron cloud.

Solutions & Oxidation Numbers

Solutions are alloys where metals or non-metals are dissolved in a metal. Oxidation number represents the electron charge of an atom in a compound.

Valence & Binary Compounds

Valence is the number of electrons an atom receives, shares, or bonds with. Binary compounds consist of two elements, such as oxides and hydrides.

Nomenclature

Systematic: Uses prefixes (mono-, di-, tri-).
Stock: Indicates valence with Roman numerals.
Traditional: Common names (e.g., H2O – water).

Acids & Salts

Hydracids: Hydrogen and non-metal (e.g., HF).
Oxoacids: Non-metal, oxygen, hydrogen (e.g., H2CO3).
Salts are formed from acid completion.

Periodic Table of Elements

Atomic Models

Dalton proposed atoms as elementary particles. Thomson included electrons. Rutherford described a nucleus with protons and a surrounding electron cloud. Neutrons were later discovered.

Atomic & Mass Number

Atomic Number (Z): Number of protons.
Mass Number: Protons + neutrons.

Isotopes

Atoms with the same number of protons but different neutrons.

Electron Configuration

Electrons are structured in energy levels. Valence electrons occupy the outermost level.

Ions

Anions: Atoms gaining electrons, negative charge.
Cations: Atoms losing electrons, positive charge.

Mendeleev’s Periodic Table

Organized elements by atomic mass and properties, leaving gaps for undiscovered elements.

Modern Periodic Table

Groups: 18 columns (alkali metals, halogens, noble gases).
Periods: 7 rows.

Metals & Non-metals

Metals: Lustrous, conductive, malleable.
Non-metals: Varied properties, often gases or poor conductors.
Semimetals: Intermediate properties.