Structure of the Atom
In this section, we explore the foundational elements of atomic theory, beginning with Dalton's initial proposition of atoms as indivisible units. As scientific inquiry progressed, it became evident that atoms are, in fact, composed of smaller subatomic particles: electrons, protons, and neutrons.
Key Discoveries
- J.J. Thomson discovered the electron in 1897, proposing a model of the atom akin to a 'Christmas pudding' where electrons are embedded in a positively charged sphere.
- Ernest Rutherford conducted the alpha-particle scattering experiment, which revealed significant insights about atomic structure, concluding that atoms have a dense nucleus containing positively charged protons, while electrons orbit this nucleus.
- Niels Bohr expanded upon Rutherford’s model by introducing distinct orbits for electrons, where electrons occupy defined energy levels.
Subatomic Particles
- Electrons (e–): Negatively charged particles with negligible mass.
- Protons (p+): Positively charged particles found within the nucleus, with a mass of approximately 1 atomic mass unit (u).
- Neutrons (n): Neutral particles also within the nucleus, with a mass close to that of protons.
Atomic Structure
The arrangement of electrons in distinct energy levels determines the atom's behavior and its chemical properties. Notably, an atom is considered stable when its outermost shell is filled, leading to higher chemical inactivity.
Concepts of Atomic Number and Mass Number
- Atomic Number (Z): The number of protons in an atom’s nucleus, fundamentally defining the element.
- Mass Number (A): The total number of protons and neutrons, influencing an atom’s overall mass.
- Isotopes: Variants of an element with the same atomic number but differing mass numbers.
- Isobars: Different elements that have the same mass number but different atomic numbers.
This exploration of the structure of the atom not only enhances our understanding of matter at a microscopic level but also lays the groundwork for advancements in chemistry and physics, influencing everything from molecular interaction to nuclear physics.