2.1 Atoms and Subatomic Particles

Atoms and Subatomic Particles

  • Definitions

    • Atom: The smallest quantity of an element that retains the unique properties of that element. For instance, an atom of hydrogen is the smallest amount of hydrogen that can exist.

    • Atoms are extraordinarily small; for perspective, the period at the end of this sentence is millions of atoms wide.

Atomic Structure and Energy

  • Subatomic Particles

    • Atoms consist of smaller subatomic particles:

    • Proton: A positively-charged particle found in the nucleus. Designated as p+.

    • Neutron: A neutral particle (no charge) found in the nucleus.

    • Electron: A negatively-charged particle that orbits around the nucleus at near light speed, designated as e−.

    • An electron's mass is roughly 1/2000th the mass of a proton or neutron.

  • Structural Models of Atoms

    • Planetary Model: Depicts electrons in fixed orbits around the nucleus, likened to planets orbiting the sun.

    • Electron Cloud Model: Illustrates electrons in varied locations around the nucleus over time, reflecting their erratic motion.

  • Electrical Charges in Atoms

    • Protons are positively charged (p+), electrons are negatively charged (e−), and neutrons are neutral.

    • The attraction between protons and electrons provides structural stability to the atom.

    • In a neutral atom, the number of protons equals the number of electrons, ensuring the overall charge is balanced.

Atomic Number and Mass Number

  • Definition of Elements

    • An atom's elemental identity is determined by the number of protons.

    • Example: Carbon is defined as an element with six protons.

    • Regardless of its location (liver or coal), every carbon atom contains exactly six protons.

  • Atomic Number

    • The atomic number of an element is defined as the number of protons present in the nucleus.

    • It also indicates the usual number of electrons present in a neutral atom.

    • Common isotopes have equal numbers of neutrons and protons; however, variations in neutrons contribute to different isotopes.

  • Mass Number

    • Calculated as the sum of protons and neutrons in the nucleus.

    • For carbon, which has 6 protons and 6 neutrons, the mass number is 12.

    • In contrast, Uranium (U) has an atomic number of 92 and a mass number of 238 (92 protons and 146 neutrons), categorizing it as a heavy metal.

Periodic Table of Elements

  • Structure of the Periodic Table

    • The periodic table organizes the 92 naturally occurring elements along with experimentally discovered heavier elements.

    • Elements are arranged by increasing atomic number, with hydrogen and helium at the top.

    • It serves as a useful reference, indicating the chemical symbol, atomic number, and mass number of elements.

    • Elements in the same column share similar reactivity based on their number of valence electrons, which are electrons involved in chemical reactions.

Isotopes

  • Definition of Isotopes

    • Isotopes are different forms of an element, defined by varying numbers of neutrons while maintaining a constant number of protons.

    • Example: Carbon has isotopes denoted as (^{12} ext{C}), typically featuring six protons and six neutrons.

    • Alternative isotopes include (^{13} ext{C}) (seven neutrons) and (^{14} ext{C}) (eight neutrons).

  • Isolation of Isotopes

    • Isotopes can also be represented in a hyphenated format (e.g., C-12 instead of 12C).

    • Hydrogen Isotopes:

    • Protium ((^{1} ext{H})): One proton, zero neutrons, most abundant hydrogen isotope.

    • Deuterium ((^{2} ext{H})): One proton, one neutron.

    • Tritium ((^{3} ext{H})): One proton, two neutrons, categorized as a heavy isotope.

  • Radioactive Isotopes

    • If an isotope contains more neutrons than usual, it is categorized as a heavy isotope.

    • Many heavy isotopes are unstable and pose as radioactive isotopes whose nucleus decays, emitting subatomic particles and electromagnetic energy.

    • Half-life: The duration it takes for half of a sample of the radioactive isotope to decay (e.g., the half-life of tritium is approximately 12 years).

  • Health Implications of Radioactivity

    • While excessive exposure to radioactive isotopes can lead to cellular damage, cancer, and birth defects, controlled exposure can have beneficial applications in medicine.