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.