Atoms: History, Models, & Structure

Atoms: History, Models, & Structure

• Atoms are the fundamental building blocks of matter and the smallest units of matter.
• All matter occupies space and has mass, and is composed of atoms.
• Greek philosophers classified matter into four primary substances: Earth, Water, Air, and Fire.
• Dmitri Mendeleev created the first periodic table of elements, building on John Dalton's earlier work.
• John Dalton proposed that elements consist of identical atoms, differentiated by atomic mass and described atoms using “eyes and hooks”.
• J.J. Thomson introduced the "plum pudding" model, depicting electrons as "plums" in a positively charged "pudding".
• Ernest Rutherford proposed the nuclear model of the atom, highlighting a small, dense positive nucleus surrounded by electrons.
• Niels Bohr likened the atom to a miniature solar system, with electrons orbiting the nucleus in fixed energy levels.
• The atom comprises three fundamental particles:
  • Electrons (-): Small, negatively charged particles orbiting the nucleus.
  • Protons (+): Positively charged particles located in the nucleus.
  • Neutrons: Electrically neutral particles in the nucleus.

Atomic Structure

• In neutral atoms, the number of electrons equals the number of protons.
• Ionization occurs when an atom gains or loses an electron, resulting in a charge.
• Electron arrangement across shells follows a specific pattern, with maximum electrons per shell calculated using 2(n^2):
  • K shell: 2 electrons
  • L shell: 8 electrons
  • M shell: 18 electrons
  • N shell: 32 electrons
  • O shell: 50 electrons
  • P shell: 72 electrons
  • Q shell: 98 electrons
• The principal quantum number (n) indicates the shell number and relates to the periodic table's structure.
• Electron binding energy varies, with K-shell electrons having higher binding energy compared to electrons in higher shells.
• Larger atoms (more protons) have electrons that are more tightly bound, requiring more energy for ionization.

Radiation: The Basics

• Radiation is divided into non-ionizing and ionizing types.
• Non-ionizing radiation includes radio waves, microwaves, infrared, and ultraviolet, lacking energy to ionize atoms.
• Ionizing radiation can remove tightly bound electrons, leading to ionization; examples include alpha, beta, neutron, and proton particles.
• Alpha particles are emitted from radioactive decay; beta particles result from neutron conversion into protons and the emission of an electron.
• Nuclear fission splits unstable atoms into smaller, more stable pieces, releasing energy and additional neutrons.

Radioactivity

• Neutral atoms have an equal number of protons and electrons, while radioactive atoms have unstable nuclei.
• Radioactive decay (disintegration) allows unstable nuclei to emit particles/energy to achieve stability.
• Radionuclides are atoms involved in radioactive decay; each atom seeks stability through this process.
• Neutron count influences nuclear stability; imbalances can lead to radioactive disintegration.
• Radioisotopes can occur naturally or be artificially produced in reactors/accelerators.
• Stability can be achieved through alpha emission (loss of 2 protons and 2 neutrons) or beta emission (neutron to proton conversion).
• Alpha emission results in a lighter atom; for example, Radium-226 becomes Radon-222 through this process.
• Beta emission alters atomic number by increasing it, changing the element type in the process.

Explore the fascinating history and models of atoms in this quiz covering influential theories and discoveries. From ancient Greek philosophy to modern atomic models proposed by Dalton, Thomson, Rutherford, and Bohr, test your understanding of the basic building blocks of matter. This quiz is a great way to deepen your knowledge of atomic structure.