Atomic Models and Periodic Table of Elements

Posted on Dec 12, 2024 in Chemistry

Atomic Models Through History

Dalton’s Atomic Model (1808)

Dalton proposed that matter is formed of small particles called atoms, which are indivisible and indestructible. He stated that all atoms of the same element are identical and that atoms of different elements are distinguished by their mass and properties. Therefore, all atoms of the same element have the same properties.

Thomson’s Plum Pudding Model (1904)

Thomson suggested that the atom was a positively charged solid sphere in which electrons were embedded, much like raisins in a pudding. Thomson’s atomic model explains the formation of ions. An ion is an atom that has gained or lost electrons. If an atom loses one or more electrons, it becomes a positive ion called a cation. If an atom gains one or more electrons, it becomes a negative ion called an anion.

Rutherford’s Model (1912)

Rutherford proposed that atoms are not solid but are mostly empty space. At its center is a tiny core called the nucleus, in which the positive particles (protons) are found. Electrons orbit the nucleus at high speed in circular orbits and are spaced at large distances from the core.

Bohr’s Model (1913)

Bohr stated that electrons revolve around the nucleus in well-defined energy levels. Each of these levels can only hold a certain number of electrons. For an electron to change from one energy level to another, it has to change its energy.

Current Atomic Model

The atom consists of a nucleus and a cortex. The nucleus is the central part of the atom and contains protons and neutrons. Protons are positively charged particles with a mass of about 1.67 x 10^-27 kg. Neutrons are uncharged particles with practically the same mass as protons. In the cortex are the electrons, which are negatively charged particles with a mass about two thousand times smaller than protons and neutrons. The electrons are distributed in different energy levels, occupying orbitals. The energy levels are from 1 to 7 in increasing order of energy (with 1 being the least energetic and 7 being the most energetic). Orbitals are regions of space around the nucleus where the probability of finding an electron is very high.

Key Concepts Related to Atomic Structure

• Isotopes: Atoms that have the same number of protons but a different number of neutrons.
• Ions:
  • Positively charged ions (cations) lose electrons, resulting in more protons than electrons.
  • Negatively charged ions (anions) gain electrons, resulting in more electrons than protons.
• Radioactivity: The loss or gain of certain particles.
• Nuclear Fission: The rupture of a nucleus to form smaller nuclei.
• Nuclear Fusion: The joining of two small atoms to form a larger nucleus.

Periodic Table of Elements

The following is a simplified representation of the periodic table.