Chapter_2_Atoms_and_Radioactivity

Chapter 2: Atoms and Radioactivity

Atoms

• Atoms are composed of smaller particles known as subatomic particles:

  • Electrons

  • Protons

  • Neutrons

• The arrangement of these particles is described by the nuclear atomic model.

Subatomic Particles

• Protons:

  • Positive charge (+)

  • Mass of about 1 amu (atomic mass unit)

• Neutrons:

  • Neutral charge (0)

  • Mass of about 1 amu

• Electrons:

  • Negative charge (-)

  • Very small mass (about 1/2000 amu)

Structure of an Atom

• Protons and neutrons are clustered together in the nucleus.

• Electrons are dispersed throughout the atom (referred to as the electron cloud).

• Most of an atom consists of empty space.

Atomic Number (Z)

• Z represents the number of protons in an atom.

• All atoms of a given element have the same atomic number, providing chemical identity.

• The atomic number is indicated above the element's symbol on the Periodic Table.

  • Example:

    • Beryllium = 4

    • Chlorine (Cl) = 17

    • Atom with Z=20 = Calcium (Ca)

    • Atom with Z=16 = Sulfur (S)

Electrons and Atoms

• Atoms are neutral; the number of electrons equals the number of protons.

  • Example:

    • Lithium (Li) has 3 protons and 3 electrons.

    • Carbon (C) has 6 protons and 6 electrons.

Isotopes

• Isotopes of an element have the same number of protons but different atomic masses.

  • Share chemical properties but differ in physical properties.

  • Some isotopes can be radioactive (radioisotopes).

• Not all isotopes are equally abundant.

Mass Number (A)

• Mass number is the total number of protons and neutrons in the nucleus: A = #protons + #neutrons.

• It correlates with the isotope but is not listed in the periodic table.

  • Example:

    • An atom with 8 protons and 10 neutrons has A = 18.

    • Carbon has A = 14, with 6 protons and 8 neutrons.

Isotopic or Nuclide Symbols

• Represent isotopes in symbols:

  • A on the top left and Z on the bottom left of the atomic symbol.

  • Example:

    • Carbon-14: [^{14}_{6}C]

Properties of Isotopes

• All isotopes share chemical identity but may exhibit different mass, stability, and radioactive properties.

Radiation

• Radiation is energy emitted from various sources, both natural and human-made:

  • Types include visible light, UV light, microwaves, and radio waves.

The Electromagnetic Radiation Spectrum

• Wavelengths of radiation range from short (gamma rays) to long (radio waves).

  • Shortest wavelengths are 0.001 nm (high energy) and longest are 1 X 10⁹ nm (low energy).

Sources of Human Exposure to Radiation

• Major sources include:

  • Medical Procedures (36%)

  • Radon and Thorium (37%)

  • Natural Sources (e.g., outer space, soil)

Nuclear Radiation and Radioactivity

• Nuclear radiation occurs when unstable isotopes emit radiation to stabilize their nucleus.

• All isotopes with atomic number 83 and higher are naturally radioactive.

Radioisotopes and Their Uses

• Specific radioisotopes are used in diagnosing and treating diseases.

  • Example uses:

    • Chromium-51 for red blood cell labeling

    • Cobalt-60 for cancer therapy.

Types of Nuclear Radiation

• Alpha (α) particles: 2 protons and 2 neutrons; relatively low penetration.

• Beta (β) particles: High-energy electrons emitted during decay.

• Gamma (γ) rays: High-energy radiation that penetrates most materials.

Radiation Effects and Safety

• Ionizing radiation can damage living cells and cause genetic mutations.

• Protective measures include lab coats, gloves, and monitoring devices (film badges).

Units of Radiation Measurement

• Rem, millirem, Sievert (Sv), millisievert (mSv).

• Average annual dose approximately 6.2 mSv.

Half-life

• Defined as the time it takes for half of a radioactive sample to decay.

• Effective half-life considers biological elimination alongside physical decay rate.

Medical Applications

• Radioisotopes are used in imaging and treating diseases (e.g., I-131 for thyroid treatment).

• Example of imaging includes PET scans, which utilize positron emissions for detection.