Chemistry Essentials for Medical Students: Matter, Isotopes, and Medical Applications

Matter and Chemistry

Matter: occupies space and has mass; composed of elements in unique combinations.
Chemistry: study of the nature, properties, and transformations of matter.
Why it matters for medical students: to understand transformations the body undergoes.

Transformation of Matter

Chemical change: transformation via reactions where one substance converts to another with different properties.
Physical change: does not alter the chemical properties of a substance.
Examples: evaporation/recovery of a solute; dissolution and energy production in the body (conceptual).

Classification of Matter

Pure substances: uniform composition; cannot be broken down chemically into simpler substances (elements) or can (compounds).
Elements: substances that cannot be chemically decomposed; consist of one type of atom.
Compounds: chemical combinations of two or more elements, can be broken down into simpler substances.
Mixtures: blend of two or more substances with their own properties.
Homogeneous: uniform composition throughout.
Heterogeneous: non-uniform composition.

Atomic Structure and Subatomic Particles

Atom: smallest unit of an element; contains nucleus and electrons.
Nucleus: contains protons (p+) and neutrons (n).
Electrons (e−): orbit nucleus; held by electromagnetic forces.
Atomic number Z: number of protons in the nucleus; identifies the element.
Mass number A: total number of protons and neutrons in the nucleus.
Neutrons n: $n = A - Z$
Neutral atom: number of protons equals number of electrons; $p^+ = e^-$ .
Ions: differ in the number of electrons; carry a net charge.

Atomic Numbers, Mass Numbers, and Neutrons

Atomic number: $Z = ext{number of protons}$ ; determines element identity.
Mass number: $A = Z + n$ ; where $n = A - Z$ is the number of neutrons.
Example (Oxygen): $Z = 8,\, A ext{ (approx)} = 16 \Rightarrow n = A - Z = 8$ ; neutral atom: $e^- = 8$ .
Example (Aluminium): $Z = 13,\, A ext{ (approx)} = 27 \Rightarrow n = 14$ ; neutral atom: $e^- = 13$ ; for \text{Al}^{3+}: e^- = 10 $.</li></ul><h3 collapsed="false" seolevelmigrated="true">Isotopes and Relative Atomic Mass</h3><ul><li>Isotopes: atoms of the same element (same$ Z $) with different$ A $due to differing numbers of neutrons.</li><li>Isotopes have the same chemical properties but different nuclear properties.</li><li>Average relative atomic mass:$ ext{Ar} =
\sumi fi Ai $where$ fi $is the isotopic fractional abundance and$ A_i $is the isotopic mass (amu).</li><li>Practical computation: combine each isotope mass with its fractional abundance to get the element’s average mass.</li></ul><h3 collapsed="false" seolevelmigrated="true">Calculations with Isotopes and Ions</h3><ul><li>Protons, neutrons, and electrons:<ul><li>For a neutral atom:$ p^+ = e^- $</li><li>General ion charge:$ ext{Charge} = p^+ - e^- $</li></ul></li><li>Example templates:<ul><li>Oxygen neutral:$ Z = 8,
A \approx 16 \Rightarrow n = A - Z = 8 \Rightarrow e^- = 8 $</li><li>Oxygen ion (O^{2-}):$ p^+ = 8,
n = 8,
e^- = p^+ - ext{charge} = 8 - (-2) = 10 $</li></ul></li><li>Aluminum neutral:$ Z = 13,
A \approx 27 \Rightarrow n = 14 \Rightarrow e^- = 13 $</li><li>Aluminum ion (Al^{3+}):$ e^- = 13 - 3 = 10 $</li></ul><h3 collapsed="false" seolevelmigrated="true">Isotopes in Medicine</h3><ul><li>Isotopes are used for detection and treatment.</li><li>Detection example: radioactive iodine,$ ^{131} ext{I} $, is used to assess thyroid function; administered as radioactive sodium iodide and measured via radiation.</li><li>Treatment example:$ ^{131} ext{I} $accumulates in thyroid cells and emits gamma radiation to kill overactive cells (hyperthyroidism).</li><li>Key idea: medical use relies on radioactive isotopes for imaging or targeted therapy.</li></ul><h3 collapsed="false" seolevelmigrated="true">Quick Reference Formulas</h3><ul><li>Neutrons:$ n = A - Z $</li><li>Ion charge:$ ext{Charge} = p^+ - e^- $(neutral:$ p^+ = e^- $)</li><li>Isotope mass averaging:$ ext{Ar} = \,\sumi fi A_i $</li><li>For neutral atoms:$ p^+ = e^- = Z $</li></ul><h5 collapsed="false" seolevelmigrated="true">Notes begin here: 1. Introduction to Chemistry</h5><ul><li>Chemistry: study of the nature, properties, and transformations of matter.</li><li>Importance for medical students: To understand the transformations the body undergoes, which are fundamentally chemical processes.</li></ul><h5 collapsed="false" seolevelmigrated="true">2. Basic Definitions</h5><ul><li>Matter: Anything that occupies space and has mass; composed of elements in unique combinations.</li><li>Transformation of Matter:<ul><li>Chemical change: A process where one substance converts into another with different chemical properties, typically through chemical reactions.</li><li>Physical change: A process that alters the physical properties of a substance (e.g., state, shape) but does not change its chemical composition.</li><li>Examples: Evaporation/recovery of a solute, dissolution processes in the body.</li></ul></li><li>Classification of Matter:<ul><li>Pure substances: Have a uniform and definite composition; can be elements or compounds.</li><li>Elements: Fundamental substances that cannot be chemically decomposed into simpler substances; consist of only one type of atom.</li><li>Compounds: Substances formed by the chemical combination of two or more elements in fixed proportions; can be broken down into simpler substances via chemical means.</li><li>Mixtures: Physical blends of two or more substances, each retaining its own distinct properties.</li><li>Homogeneous mixtures: Have a uniform composition and appearance throughout (e.g., saltwater).</li><li>Heterogeneous mixtures: Have a non-uniform composition, with visibly distinct phases or regions (e.g., sand and water).</li></ul></li></ul><h5 collapsed="false" seolevelmigrated="true">3. Atomic Structure and Related Concepts</h5><ul><li>Atom: The smallest unit of an element that retains the chemical properties of that element; consists of a nucleus and orbiting electrons.<ul><li>Nucleus: The dense central part of an atom, containing protons and neutrons.</li><li>Protons ($ p^+ $): Positively charged subatomic particles located in the nucleus.</li><li>Neutrons ($ n $): Neutrally charged subatomic particles located in the nucleus.</li><li>Electrons ($ e^- $): Negatively charged subatomic particles that orbit the nucleus; held by electromagnetic forces.</li></ul></li><li>Atomic number ($ Z $): The number of protons in the nucleus of an atom; uniquely identifies an element.</li><li>Mass number ($ A $): The total number of protons and neutrons in the nucleus of an atom.<ul><li>Number of neutrons ($ n $) can be calculated as:$ n = A - Z $</li></ul></li><li>Isotopes: Atoms of the same element (i.e., having the same atomic number,$ Z $) but with different mass numbers ($ A $) due to varying numbers of neutrons.<ul><li>Isotopes have identical chemical properties but may have different nuclear properties.</li></ul></li></ul><h5 collapsed="false" seolevelmigrated="true">4. Identifying Subatomic Particles</h5><ul><li>For a neutral atom: The number of protons ($ p^+ $) is equal to its atomic number ($ Z $), and the number of electrons ($ e^- $) is equal to the number of protons ($ e^- = p^+ $).</li><li>For an ion: The number of electrons ($ e^- $) differs from the number of protons ($ p^+ $), resulting in a net electrical charge.<ul><li>General ion charge:$ \text{Charge} = p^+ - e^- $</li></ul></li><li>Examples:<ul><li>Oxygen (O), neutral atom: Atomic number$ Z = 8 $, Mass number$ A \approx 16 $(given as example).</li><li>Protons ($ p^+ $):$ 8 $(since$ Z = 8 $)</li><li>Neutrons ($ n $):$ A - Z = 16 - 8 = 8 $</li><li>Electrons ($ e^- $):$ 8 $(since neutral atom,$ p^+ = e^- $)</li><li>Oxygen ion (O$ ^{2-} $):</li><li>Protons ($ p^+ $):$ 8 $</li><li>Neutrons ($ n $):$ 8 $</li><li>Electrons ($ e^- $):$ p^+ - \text{charge} = 8 - (-2) = 10 $</li><li>Aluminium (Al), neutral atom: Atomic number$ Z = 13 $, Mass number$ A \approx 27 $(given as example).</li><li>Protons ($ p^+ $):$ 13 $</li><li>Neutrons ($ n $):$ A - Z = 27 - 13 = 14 $</li><li>Electrons ($ e^- $):$ 13 $</li><li>Aluminium ion (Al$ ^{3+} $):</li><li>Protons ($ p^+ $):$ 13 $</li><li>Neutrons ($ n $):$ 14 $</li><li>Electrons ($ e^- $):$ p^+ - \text{charge} = 13 - (+3) = 10 $</li></ul></li></ul><h5 collapsed="false" seolevelmigrated="true">5. Relative Atomic Mass</h5><ul><li>Definition: The average relative atomic mass ($ \text{Ar} $) of an element is the weighted average of the masses of its naturally occurring isotopes, taking into account their fractional abundances.</li><li>Calculation: It is calculated using the formula:$ \text{Ar} = \sum{i} f{i} A_{i} $where:<ul><li>$ f_{i} $is the isotopic fractional abundance of isotope$ i $(the fraction of that isotope in the natural sample).</li><li>$ A_{i} $is the isotopic mass (in atomic mass units, amu) of isotope$ i $.</li><li>Practical computation: To calculate the average relative atomic mass, multiply the mass of each isotope by its fractional abundance and then sum these products.</li></ul></li></ul><h5 collapsed="false" seolevelmigrated="true">6. Medical Applications of Isotopes (Example: Iodine-131)</h5><ul><li>Isotopes, particularly radioactive isotopes, are widely used in medicine for both diagnostic detection and therapeutic treatment due to their unique nuclear properties.</li><li>Iodine-131 ($ ^{131}\text{I} $) as an example:<ul><li>Detection (Diagnosis): Used to assess thyroid gland function.</li><li>Administered as radioactive sodium iodide, which mimics non-radioactive iodine and is readily absorbed by thyroid cells.</li><li>The uptake and distribution of the$ ^{131}\text{I} $in the thyroid can be measured externally using radiation detectors, providing information about thyroid activity (e.g., hyperthyroidism, hypothyroidism, or the presence of nodules).</li><li>Treatment (Therapy): Used to treat hyperthyroidism and certain types of thyroid cancer.</li><li>When administered in higher doses, the$ ^{131}\text{I}$$ concentrates in the overactive thyroid cells.
It emits gamma radiation, which destroys the hyperactive or cancerous thyroid cells, reducing hormone production or eliminating cancerous tissue.

Key Idea: The medical utility of radioactive isotopes stems from their ability to be selectively incorporated into specific tissues or organs and their emission of detectable or therapeutic radiation.