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Understanding Elements and Atoms

May 16, 2025

2.1 Elements and Atoms: The Building Blocks of Matter

Key Concepts

  • Matter: Anything that occupies space and has mass.
    • Mass vs Weight: Mass is constant regardless of location, but weight varies with gravity.

Elements and Compounds

  • Element: A substance that cannot be broken down by chemical means.
    • Example: Calcium (Ca) is essential and must be ingested.
  • Compound: Formed by two or more elements chemically bonded.
    • Example: Glucose (C, H, O) is a compound used as fuel in the body.

Atoms and Subatomic Particles

  • Atom: Smallest unit of an element, retaining its properties.
    • Composed of protons, neutrons, electrons.
    • Atoms have a nucleus (protons + neutrons) and electron cloud.
  • Subatomic Particles:
    • Proton: Positive charge (p+)
    • Neutron: No charge
    • Electron: Negative charge (e-)

Atomic Structure and Energy

  • Protons and Electrons: Equal numbers in a neutral atom, balancing charges.
  • Atomic Number: Number of protons, identifies the element.
  • Mass Number: Sum of protons and neutrons.
  • Periodic Table: Arranges elements by atomic number and properties.

Isotopes

  • Variations of elements with different neutron numbers.
  • Heavy Isotopes: Unstable, radioactive, used in medical imaging (e.g., PET scans).

Interventional Radiology

  • Uses radioisotopes for non-surgical treatment (e.g., treating liver tumors via radioembolization).

The Behavior of Electrons

  • Electrons occupy electron shells.
    • Shells determine an atom's energy level and reactivity.
    • Valence Shell: Outer shell, crucial for chemical reactions.
  • Octet Rule: Atoms tend to have eight electrons in their valence shell for stability.
  • Chemical Bonds: Arise from electron sharing or transfer to fill valence shells.
    • Example: Water formation from hydrogen and oxygen.

Study Tips

  • Familiarize with the periodic table to understand element relationships.
  • Focus on understanding atomic structure and electron behavior for chemical reactivity insights.
  • Recognize the role of isotopes in both natural processes and medical applications.