Introduction to Chemistry

Basic Structure of an Atom

Nucleus: Contains protons and neutrons
- Protons (p+): Positive charge (+1)
- Neutrons (n⁰): Neutral charge (0)
Electrons (e–): Surround nucleus; Negative charge (-1)
Overall charge of atom is neutral when number of protons equals number of electrons.

Elements making up 96% of human body: Carbon (C), Oxygen (O), Hydrogen (H), Nitrogen (N)
Major elements include: Calcium (Ca), Phosphorus (P), Potassium (K), Sodium (Na), Chloride (Cl), Magnesium (Mg)
Trace elements: Needed in very small quantities but essential for life.

Atomic Number: Number of protons in the nucleus, defines the element (e.g., Hydrogen has 1 proton, Helium has 2 protons)
Atomic Mass: Sum of protons, neutrons, and electrons’ mass (less emphasized at this point)

Isotopes: Variants of an element with the same number of protons but different numbers of neutrons.
Example: Oxygen typically has 8 protons and if it has different numbers of neutrons, it forms isotopes.
Unstable Isotopes: Radioactive due to excess neutrons causing decay (e.g., Iodine-131 used in medical treatments)
- Radioactivity: Emission of alpha, beta, or gamma radiation
- Medical Uses: As tracers to monitor radioactivity and targeted treatments such as shrinking tumors.

Ions form when atoms gain or lose electrons, leading to a net positive or negative charge.
- Cations (+): Lose electrons (e.g., Sodium -> Na⁺)
- Anions (−): Gain electrons (e.g., Chloride -> Cl⁻)
Important Ions in Physiology: Sodium (Na⁺), Potassium (K⁺), Calcium (Ca²⁺), Chloride (Cl⁻), Phosphate (PO₄³⁻)

Role of Electrons:
- Form bonds: Covalent, ionic, hydrogen bonds
- Free radicals: Unstable molecules with free electrons, mitigated by antioxidants.

Ionic Bonds: Transfer of electrons between atoms
- Common in salts (e.g., NaCl)
Covalent Bonds: Shared electrons between atoms
- Types: Polar (unequal sharing, creates dipoles, e.g., H₂O) and Nonpolar (equal sharing, e.g., CH₄)
Hydrogen Bonds: Weak interactions between polar molecules
- Important in cohesion and high heat capacity of water

Polar Molecules: Unequal distribution of charge (e.g., Water)
- Water is essential due to its hydrogen bonding and properties like high heat capacity and surface tension.
Nonpolar Molecules: Equal distribution of charge (e.g., Methane)

Cohesion and Surface Tension: Due to hydrogen bonds, important in phenomena such as surface tension in liquids.
Biological Relevance: High heat capacity critical for life processes; surfactants in lungs reduce surface tension, aiding in breathing for premature infants.

Changing the number of protons changes the element.
Changing the number of neutrons forms isotopes.
Changing the number of electrons forms ions.
Understanding bond types and polarity is crucial for understanding molecular interactions.
Water’s unique properties underlie many biological processes and its role in physiology is unparalleled.

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