Chemistry Comes Alive: Matter, Energy, and Atomic Structure

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Chemistry Comes Alive

Matter and Energy

Understanding the basic concepts of matter and energy is fundamental to the study of anatomy and physiology, as all living things are composed of matter and require energy to function.

Matter: Anything that occupies space and has mass. Most matter can be seen, smelled, or felt.
Mass vs. Weight:
- Mass: The actual amount of matter in an object; remains constant regardless of location or gravity.
- Weight: The force exerted by gravity on an object; varies with gravity.

States of Matter

Solid: Definite shape and volume (e.g., bones, teeth).
Liquid: Definite volume, conforms to container shape (e.g., blood plasma).
Gas: No definite shape or volume (e.g., air in lungs).

Energy: The Mover of Matter

Energy: The capacity to do work or put matter into motion. It has no mass and does not occupy space, but its effects can be measured.
Relationship to Matter: Matter is the substance; energy moves or changes that substance.

Kinetic vs. Potential Energy

Kinetic Energy: Energy in action (e.g., moving atoms, a bouncing ball).
Potential Energy: Stored energy with the potential to do work (e.g., energy stored in chemical bonds, water behind a dam).
Energy Conversion: Energy can be transformed from potential to kinetic and vice versa. For example, opening a dam releases potential energy as kinetic energy.

Forms of Energy Used by the Body

Chemical Energy: Stored in chemical bonds; released during chemical reactions. Example: Energy from food is stored in ATP, which releases energy when its bonds are broken.
Electrical Energy: Results from movement of charged particles (ions). Example: Nerve impulses and muscle contractions rely on electrical currents.
Mechanical Energy: Directly involved in moving matter. Example: Muscle contractions moving limbs.
Radiant/Electromagnetic Energy: Travels in waves (e.g., visible light, UV, X-rays). Example: Visible light enables vision; UV light helps synthesize vitamin D.

Energy Conversion and Inefficiency

Energy conversions are never 100% efficient; some energy is always lost as heat.
In the body, heat maintains body temperature and increases the rate of chemical reactions.

Elements and Atoms

All matter is composed of elements, which are pure substances that cannot be broken down by ordinary chemical means. Atoms are the smallest units of elements that retain their properties.

Major Elements of the Human Body

Oxygen (O): ~65% of body mass; essential for ATP production.
Carbon (C): ~18.5%; backbone of all organic molecules.
Hydrogen (H): ~9.5%; influences pH as a proton (H+).
Nitrogen (N): ~3.2%; found in proteins and nucleic acids.

Lesser Elements (3.9% of Body Mass)

Calcium (Ca): Bones/teeth; muscle contraction, nerve impulses, blood clotting ().
Phosphorus (P): Bones/teeth, nucleic acids, ATP.
Potassium (K): Major intracellular cation (); nerve/muscle function.
Sulfur (S): Component of proteins.
Sodium (Na): Major extracellular cation (); water balance, nerve/muscle function.
Chlorine (Cl): Major extracellular anion ().
Magnesium (Mg): Bone; metabolic cofactor.
Iodine (I): Thyroid hormone synthesis.
Iron (Fe): Hemoglobin, enzymes.

Atomic Symbols

One- or two-letter abbreviations (e.g., O for oxygen, Na for sodium).
Some symbols derive from Latin names (e.g., Na for natrium, K for kalium).

Atomic Structure

Atoms consist of a central nucleus containing protons and neutrons, surrounded by electrons in orbitals.

Proton: Positive charge, 1 atomic mass unit (amu), in nucleus.
Neutron: No charge, 1 amu, in nucleus.
Electron: Negative charge, negligible mass (~0 amu), in orbitals.

Structural Models of the Atom

Planetary Model: Electrons orbit nucleus in fixed paths (outdated).
Orbital Model: Electrons occupy regions of probability (electron clouds); more accurate for predicting chemical behavior.

Identifying Elements

Atomic Number: Number of protons in the nucleus; unique to each element.
Mass Number: Total number of protons and neutrons.
Isotopes: Atoms of the same element with different numbers of neutrons (same atomic number, different mass number).
Atomic Weight: Average of mass numbers of all isotopes of an element.

Radioisotopes

Radioisotopes: Unstable isotopes that decay, emitting radiation.
Radioactivity: Energy released during decay; can be detected and measured.
Clinical Applications: Used in medical imaging and cancer treatment due to their chemical similarity to stable isotopes.
Toxicity: All radioactivity can damage living tissue; some forms cause cancer, while others are used therapeutically.

Table: Major and Lesser Elements in the Human Body

Element	Symbol	Body Mass (%)	Main Functions
Oxygen	O	~65.0	Component of water and organic molecules; required for ATP production
Carbon	C	~18.5	Backbone of all organic molecules
Hydrogen	H	~9.5	Component of water and organic molecules; influences pH
Nitrogen	N	~3.2	Component of proteins and nucleic acids
Calcium	Ca	Variable	Bones/teeth, muscle contraction, nerve function, blood clotting
Phosphorus	P	Variable	Bones/teeth, nucleic acids, ATP
Potassium	K	Variable	Major intracellular cation, nerve/muscle function
Sulfur	S	Variable	Component of proteins
Sodium	Na	Variable	Major extracellular cation, water balance, nerve/muscle function
Chlorine	Cl	Variable	Major extracellular anion
Magnesium	Mg	Variable	Bone, metabolic cofactor
Iodine	I	Variable	Thyroid hormone synthesis
Iron	Fe	Variable	Hemoglobin, enzymes

Key Equations

Atomic Number:
Mass Number:
Atomic Weight:

Example: Isotopes

Carbon-12: 6 protons, 6 neutrons (mass number = 12)
Carbon-14: 6 protons, 8 neutrons (mass number = 14)
Both are isotopes of carbon, differing only in neutron number.

Additional info: Understanding atomic structure and the properties of elements is essential for grasping how molecules form and interact in the body, which underpins all physiological processes.