Understanding Atoms, Elements, and Chemical Bonds

Posted on Mar 30, 2025 in Chemistry

The Atom: Building Block of Matter

The atom is the fundamental unit of matter, consisting of protons, neutrons, and electrons.

Subatomic Particles

  • Electron: Mass approximately 10-31 kg. Discovered by J.J. Thomson.
  • Proton: Located in the nucleus, with a mass approximately 1840 x 10-31 kg. Discovered by Rutherford in 1919.
  • Neutron: Located in the nucleus, with a mass approximately 1840 x 10-31 kg. Discovered by Chadwick in 1932.

Atomic Models

  • Thomson Model: Proposed in 1904, suggesting the atom consists of a sphere of positively charged matter with embedded electrons. Introduced the concept of electrons.
  • Rutherford Model: Proposed in 1911, suggesting the atom is composed of a nucleus with electrons revolving around it in circular orbits. Introduced the concept of the atomic nucleus and the separation of positive and negative charges.
  • Bohr Model: Proposed in 1930, suggesting electrons move in definite orbits with different energy levels. Introduced the concept of energy levels for electrons.
  • Current Model: Atoms are electrically neutral, containing equal numbers of protons and electrons, along with neutrons. Protons and neutrons reside in the positively charged nucleus. Electrons form the electron cloud, arranged in energy levels and orbitals. Atoms can absorb or emit energy, causing electrons to transition between energy levels.

Characteristics of Atoms

  • Atomic Number (Z): Indicates the number of protons in the atom.
  • Mass Number (A): Indicates the sum of protons and neutrons in an atom.
  • Neutral Atoms: Can lose or gain electrons to form ions.
  • Ions:
    • Positive ions (cations): Formed when an atom loses electrons.
    • Negative ions (anions): Formed when an atom gains electrons.
  • Isotopes: Atoms with the same atomic number but different mass numbers, meaning they are atoms of the same element with different numbers of neutrons.

Electronic Configuration

Electronic configuration describes the distribution of electrons within an atom’s energy levels and orbitals.

Atoms have 7 electron shells (K, L, M, N, O, P, Q). Each shell contains one or more orbitals (s, p, d, f) with slightly different energy levels. The first shell has only the 1s orbital, the second has 2s and 2p, and the third and higher shells include d and f orbitals.

Orbital capacities:

  • s = 2 electrons
  • p = 6 electrons
  • d = 10 electrons
  • f = 14 electrons

Shell capacities:

  • K = 2 electrons
  • L = 8 electrons
  • M = 18 electrons
  • N = 32 electrons

Chemical Elements

An element is a substance that cannot be broken down into simpler substances by chemical means. It consists of only one type of atom.

Metals

  • Exhibit metallic luster.
  • Good conductors of electricity and heat.
  • Malleable and ductile.
  • High density and melting points.
  • Generally hard.
  • Combine with non-metals and are easily oxidized.

Non-metals

  • Dull appearance.
  • Poor conductors (insulators).
  • Brittle and not easily deformed.
  • Low density and melting points.
  • Generally soft.
  • Combine with other non-metals and metals, and do not easily undergo oxidation.

Historical Development of Element Classification

  • Triads (Döbereiner, 1851): Grouped elements into sets of three with similar chemical properties.
  • Law of Octaves (Newlands, 1864): Ordered elements by atomic weight and grouped them into sets of seven based on similar properties.
  • Mendeleev and Meyer’s Periodic Table (1870): Developed a periodic table sorting elements by atomic mass and properties.
  • Modern Periodic Table: Sorts elements by increasing atomic number (Z).

Chemical Compounds

A chemical compound is a pure substance that can be broken down into simpler substances by chemical processes and consists of multiple types of atoms.

Classification of Chemical Compounds

  • Organic compounds: Compounds containing carbon.
  • Inorganic compounds: Compounds that do not contain carbon.
  • Ionic compounds: Formed through ionic bonds.
  • Covalent compounds: Formed through covalent bonds.

Chemical Bonding

  • Ionic Bond: The electrostatic attraction between ions of opposite charges. Typically formed when a metal atom transfers electrons to a nonmetal atom.
    Properties: Crystalline solids with high melting and boiling points, often soluble in water.
  • Covalent Bond: The sharing of one or more pairs of electrons between atoms to form a molecule.
    Properties: Can exist in solid, liquid, or gaseous states, with low melting and boiling points. Often poorly soluble in water.
  • Metallic Bond: The sharing of electrons among a lattice of metal atoms.
    Properties: Exhibit metallic luster, good conductors of electricity and heat, and are oxidized by oxygen in the air.