Atomic Models and Chemical Bonding: A Comprehensive View

Posted on Jan 31, 2025 in Chemistry

Atomic Models

Dalton Model

  • Each element is composed of indivisible particles called atoms.
  • In an element, all the atoms are identical.
  • Atoms of different elements are all different.
  • When atoms of more than one element combine, they form molecules. Compounds are made of molecules.
  • In a chemical reaction, atoms are not created, destroyed, or changed into other types of atoms.

Thomson Model

Thomson based this model on his work with cathode rays. In this model, an atom consists of a positively charged jellylike matter with negative electrons scattered throughout it.

  1. Electrization is the possibility of taking electrons from one atom to others.
  2. Existence of ions:
    • Cation (+): atom with a lack of electrons
    • Anion (-): atom with an excess of electrons

Rutherford Model

Rutherford bombarded a thin sheet of gold with alpha particles and realized that nearly all alpha particles got through the sheet with no deviation, and a few ones suffered deviation. The conclusions for this experiment were that:

  • Most of the volume of the atom is empty space.
  • Most of the mass of the atom is concentrated in a dense, positively charged nucleus.
  • Electrons are spinning around the nucleus very far from it.

Bohr Model

Atoms:

  • Nucleus: Positively charged and with nearly all the mass of the atom: protons (+), and neutrons (no electric charge).
  • Electrons: Negatively charged, spinning around the nucleus very far from it. Electrons can only be in some allowed orbits.
  • If one electron absorbs energy, it jumps to another orbit.
  • If one electron emits energy, it jumps back to a lower orbit.
  • An electron in equilibrium in one orbit doesn’t emit or absorb energy; it is stationary.

Chemical Bonding

Ionic Bonding

Appears between a metal and a nonmetal. Metals tend to give electrons, and nonmetals tend to accept them. When a metal gives one or more electrons to a nonmetal, it becomes a cation, and the nonmetal becomes an anion. As anions and cations are oppositely charged, an electric attraction force appears between them, and they get together, forming an ionic bond.

Properties

  • They form crystals, very hard but fragile.
  • They dissolve in polar solvents.
  • They have very high melting and boiling points.
  • They conduct electricity in solution but not by themselves.

Covalent Bonding

Covalent bonding happens between nonmetals. They share electrons in pairs in order to get the structure of noble gases. This is called the octet rule. If one pair of electrons is shared, they form a simple bond. If two pairs are shared, it will be a double bond, and if three pairs are shared, it will be a triple bond.

Properties

  • They don’t conduct electricity.

Covalent Substances

  • Molecular substances: H2O, CO2, CH4, NH3, H2, O2, N2, Cl2.
  • They are all gases or liquids.
  • They have very low melting and boiling points.

Covalent Crystals

  • They are hard crystals or solids.
  • They have high melting and boiling points.

Metallic Bonding

  • Kernels of metal atoms that are formed by all the nuclei of the metal atoms and the full levels of inner electrons. These kernels form a crystal net, very stable.
  • Mobile valence electrons are the electrons that are very far from their nuclei, and they are free to move all around the net of kernels and don’t belong to any atom but to the whole net.

Properties

  • They are very hard, strong, and dense because of the great stability of their nets.
  • They have very high melting and boiling points; they are all solids except for mercury.
  • They have very high thermal and electrical conductivity.
  • They are malleable and ductile (we can make thin foils and threads with them).
  • They are brittle.