Chemical Principles in Anatomy & Physiology: Matter, Energy, Atoms, Elements, and Mixtures

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Chemical Principles

Matter and Energy

Understanding 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 is anything that occupies space and has mass. It includes gases, liquids, and solids.
Mass is the amount of matter (or chemical substance) in an object and remains constant regardless of location.
Weight reflects gravity's effect on mass and can vary depending on location (e.g., astronauts are weightless in space but have the same mass).
Energy is less tangible than matter, has no mass, does not occupy space, and is measured by its effects on matter. It is defined as the capacity to do work or put matter into motion.
Key Point: Matter is the substance; energy is the mover of the substance.
All living things require energy for growth and function; energy use gives us "life."
Example: A baseball player who hits a ball over the fence uses more energy than a batter who just bunts the ball.

Composition of Matter: Atoms and Elements

Atoms

Atoms are the basic building blocks of matter and are the smallest units of elements that retain the properties of the element.

Each element is composed of more or less identical particles called atoms.
Atoms are extremely small, typically less than 0.1 nanometers in diameter ( inch).
Atoms of each element differ from those of other elements, giving each element unique physical and chemical properties.
Physical properties are detectable by senses (e.g., color, temperature, texture).
Chemical properties pertain to how atoms interact with other atoms (bonding behavior).
Example: Iron rusts, gasoline burns in air, animals digest food.

Elements

Elements are fundamental substances that cannot be broken down into simpler substances by ordinary chemical methods.

Common elements in the human body include: Oxygen, Carbon, Hydrogen, Nitrogen, Calcium, Phosphorus, Potassium, Sulfur, Sodium, Chlorine, Magnesium, Iodine, Iron, Chromium, Cobalt, Copper, Fluorine, Manganese, Molybdenum, Selenium, Silicon, Tin, Vanadium, Zinc.
Four elements make up about 96% of body weight: Carbon, Oxygen, Hydrogen, Nitrogen.

Element Symbols

Each element is designated by a one- or two-letter chemical shorthand called an atomic symbol.

Usually, the symbol uses the first letter(s) of the element's name (e.g., C = carbon, O = oxygen, Ca = calcium).
Some symbols are derived from Latin names (e.g., Na = sodium, from natrium).

Atomic Structure

Subatomic Particles

Atoms consist of smaller particles: protons, neutrons, and electrons, each differing in mass, charge, and position.

Protons: Positive charge, located in the nucleus.
Neutrons: Neutral charge, located in the nucleus.
Electrons: Negative charge, orbiting the nucleus; charge equal in magnitude to the proton's positive charge.
Atoms are electrically neutral overall, meaning equal numbers of protons and electrons.
Example: Hydrogen atom has one proton and one electron, no neutrons.

Atomic Structure Diagram

Additional info: The nucleus contains protons and neutrons, while electrons orbit in shells around the nucleus.

Identifying Elements

Atomic Number

The atomic number is a key identifier for elements.

Atomic number = number of protons in the nucleus.
Written as a subscript to the left of the atomic symbol (e.g., for hydrogen).
Since the number of protons equals the number of electrons in a neutral atom, atomic number also indicates the number of electrons.

Mass Number

The mass number is the sum of protons and neutrons in an atom.

Mass number = number of protons + number of neutrons.
Electrons have negligible mass and are ignored in mass calculations.
Written as a superscript to the left of the atomic symbol (e.g., for carbon-12).
Isotopes are atoms of the same element with different numbers of neutrons (and thus different mass numbers).
Example: Carbon has three isotopes: (6 protons, 6 neutrons), (6 protons, 7 neutrons), (6 protons, 8 neutrons).

Atomic Weight (Atomic Mass)

Atomic weight is the average of the relative weights (mass numbers) of all isotopes of an element, considering their abundance in nature.

Atomic weight is approximately equal to the mass number of the most abundant isotope.
Example: Hydrogen's atomic weight is 1.008, indicating its lightest isotope is most abundant.

Radioisotopes

Radioactivity and Isotopes

Some isotopes are unstable and undergo radioactive decay, emitting particles or energy from their nucleus.

Types of radioactive emission: Alpha, Beta, Gamma.
Alpha rays: lowest penetrating power, least damaging to tissue.
Gamma rays: highest penetrating power, most damaging.
Each radioisotope has a characteristic half-life, the time required for half of its atoms to decay.
Half-lives vary from hours to thousands of years.

Molecules and Compounds

Molecules

Atoms rarely exist alone; they combine chemically to form molecules.

If two or more atoms of the same element combine, the result is a molecule of that element (e.g., , ).
Example: Two hydrogen atoms bond to form hydrogen gas (); two oxygen atoms bond to form oxygen gas ().

Compounds

Compounds are formed when two or more different kinds of atoms bind together.

Example: Two hydrogen atoms and one oxygen atom form water (); four hydrogen atoms and one carbon atom form methane ().
Compounds are chemically pure substances; all molecules of a compound are identical.
A molecule is the smallest particle of a compound that retains its specific characteristics.
Properties of compounds are usually very different from those of the atoms they contain.

Classes of Compounds

Organic compounds: Contain carbon; usually covalently bonded and often large molecules.
Inorganic compounds: Do not contain carbon (exceptions: carbon dioxide and carbon monoxide are considered inorganic). Examples include water, salts, acids, and bases.

Mixtures

Types of Mixtures

Mixtures are substances composed of two or more components physically intermixed. Most matter exists as mixtures, which are classified into three basic types:

Solutions: Mixtures of two or more components that may be gases, liquids, or solids. The substance in greatest quantity is the solvent (usually water in the body), and substances in smaller amounts are solutes.
True solutions are transparent; solutes are minute and do not settle out or scatter light.
Concentration of a solution is often expressed in molarity (moles per liter):
Colloids: Mixtures with larger solute particles than solutions; appear translucent or milky, scatter light, but do not settle out. Colloids can undergo sol-gel transformations (e.g., Jell-O, cytoplasm in cells).
Suspensions: Mixtures with large, visible solutes that tend to settle out unless kept in suspension by mixing or movement (e.g., blood cells in plasma).

Mixtures vs. Compounds

Mixtures do not involve chemical bonding between components; compounds do.
Mixture components can be separated by physical means (straining, filtering, evaporation); compounds require chemical means (breaking bonds).
Properties of atoms or molecules are unchanged in mixtures but altered in compounds.

Table: Key Elements in the Human Body

Element	Atomic Number	Mass Number	Atomic Mass	Role in Body
Hydrogen (H)	1	1	1.008	Component of water and organic molecules
Carbon (C)	6	12	12.01	Backbone of organic molecules
Nitrogen (N)	7	14	14.01	Component of proteins and nucleic acids
Oxygen (O)	8	16	16.00	Essential for cellular respiration
Sodium (Na)	11	23	22.99	Electrolyte, nerve impulse transmission
Chlorine (Cl)	17	35	35.45	Electrolyte, acid-base balance
Potassium (K)	19	39	39.10	Electrolyte, muscle contraction

Table: Types of Mixtures

Type	Particle Size	Appearance	Settling	Example
Solution	Small (atoms, ions, molecules)	Transparent	No settling	Salt water, plasma
Colloid	Intermediate	Translucent/milky	No settling	Cytoplasm, Jell-O
Suspension	Large (visible particles)	Opaque	Settles out	Blood cells in plasma

Additional info: These chemical principles form the foundation for understanding cellular structure, metabolism, and physiological processes in the human body.