Chemistry Foundations for Anatomy & Physiology

Matter

Definition and States of Matter

Matter is anything that has mass and occupies space. In the context of anatomy and physiology, understanding matter is essential because all living organisms are composed of matter in various forms.

• Solid – Definite shape and volume.

• Liquid – Definite volume, changeable shape.

• Gas – Changeable shape and volume.

Energy

Types and Forms of Energy

Energy is the capacity to do work or put matter into motion. It is fundamental to physiological processes such as muscle contraction and nerve impulse transmission.

• Kinetic energy – Energy in action.

• Potential energy – Stored (inactive) energy.

Forms of energy include:

• Chemical – Stored in the bonds of chemical substances.

• Electrical – Results from movement of charged particles.

• Mechanical – Directly involved in moving matter.

• Radiant/Electromagnetic – Energy traveling in waves (e.g., visible light, ultraviolet light, X-rays).

Composition of Matter

Elements and Atoms

Elements are substances that cannot be broken down by ordinary chemical means. Atoms are the building blocks of each element.

• Major elements of the human body: Carbon (C), Hydrogen (H), Nitrogen (N), Oxygen (O). These make up about 96% of the human body.

• Lesser elements: Calcium (Ca), Phosphorus (P), Potassium (K), Sulfur (S), Sodium (Na), Chlorine (Cl). These make up about 3.9% of the body.

• Trace elements: Make up less than 0.01% of the body and are required in minute amounts, often as part of enzymes.

Atomic Structure

Subatomic Particles

An atom is the smallest subdivision of an element. Atoms consist of subatomic particles:

• Electrons – Negative charge, found in the orbits around the nucleus, mass is 1/2000 that of a proton.

• Protons – Positive charge, found in the nucleus, mass of 1 atomic mass unit (amu).

• Neutrons – No charge, found in the nucleus, mass of 1 amu.

Electrons usually equal the number of protons, making the atom electrically neutral.

• Atomic number – Number of protons.

• Mass number – Total number of protons and neutrons.

• Atomic weight – Average of the mass numbers of all isotopes.

• Isotopes – Atoms of the same element with different numbers of neutrons.

Example:

• $^{12}C$ (6 protons + 6 neutrons) – stable

• $^{14}C$ (6 protons + 8 neutrons) – unstable

Atomic Radiation

Some isotopes emit radiation, known as atomic radiation. Types include:

• Alpha – Slow and non-penetrating.

• Beta – Faster and penetrating.

• Gamma – Very fast and deeply penetrating.

Radioisotopes have clinical uses in medical imaging and treatment.

Models of the Atom

• Planetary Model – Electrons move around the nucleus in fixed, circular orbits.

• Orbital Model – Regions around the nucleus where electrons are most likely to be found.

Chemical Bonds and Compounds

Molecules, Compounds, and Mixtures

Chemical bonds hold atoms together to form molecules and compounds. Mixtures are physical combinations of substances, while compounds are chemical combinations.

• Molecule – Two or more atoms held together by chemical bonds.

• Compound – Two or more different kinds of atoms chemically bonded together.

• Mixture – Two or more components physically intermixed (not chemically bonded).

• Solution – Homogeneous mixture of components.

• Solvent – Substance present in greatest amount in a solution.

Concentration of Solutions

• Expressed by percent (e.g., 10%, 20%) or parts (ppm, ppb).

Molarity (Moles per Liter)

• One mole of an element or compound equals its atomic or molecular weight (sum of atomic weights) in grams.

Colloids and Suspensions

• Colloids (emulsions) – Heterogeneous mixtures whose solutes do not settle out.

• Suspensions – Heterogeneous mixtures with visible solutes that tend to settle out.

Mixtures Compared with Compounds

• No chemical bonding in mixtures.

• Mixtures can be separated by physical means; compounds cannot.

• Mixtures can be heterogeneous or homogeneous; all compounds are homogeneous.

Chemical Bonds

Types of Chemical Bonds

Atoms combine by bonds, which are attractive forces holding atoms together. Bonds are formed using electrons in the outermost energy level (valence shell).

• Octet rule – Atoms react to have 8 electrons in their valence shell.

• Formula to calculate number of electrons in an orbit: $2n^2$

Covalent Bond

• Formed by sharing of electrons.

• Most important bond for biological molecules.

• Single bond: Sharing one pair of electrons.

• Double bond: Sharing two pairs of electrons.

• Electrons shared equally produce nonpolar molecules (e.g., $H_2$, $N_2$, $CO_2$).

• Unequal sharing produces polar molecules (e.g., $H_2O$, glucose).

Ionic Bond

• Formed when atoms gain or lose electrons to become ions.

• Ions are charged atoms: cations (+), anions (−).

• The bond between ions is the ionic bond.

• Example: $Na^+ + Cl^- \rightarrow NaCl$

• Electrons are donated, not shared.

• Atoms are linked by opposite charges.

• Ionic compounds form crystals instead of individual molecules.

Hydrogen Bond

• Formed between a hydrogen atom and two other atoms (one must be oxygen or nitrogen).

• Very weak bond, rapidly formed and broken.

• Important in biological systems (e.g., water molecules, DNA, proteins).

Chemical Reactions

Types of Chemical Reactions

Chemical reactions occur when chemical bonds are formed, rearranged, or broken. Reactions contain reactants and products, and are written in symbolic form using chemical equations.

• Synthesis reaction – Reactant molecules combine to form larger molecules. $A + B \rightarrow AB$

• Decomposition reaction – Reactant molecules break down to form simpler molecules. $AB \rightarrow A + B$

• Exchange reaction – Reactant molecules change positions. $AB + CD \rightarrow AC + BD$

• Reversible reaction – Products can change back to reactants. $A + B \rightleftharpoons AB$

Summary Table: Major and Lesser Elements of the Human Body

Element	Symbol	Approximate % of Body	Function
Carbon	C	18.5%	Primary component of all organic molecules
Hydrogen	H	9.5%	Component of water and most organic molecules
Nitrogen	N	3.2%	Component of proteins and nucleic acids
Oxygen	O	65%	Component of water; needed for cellular respiration
Calcium	Ca	1.5%	Component of bones and teeth; needed for muscle contraction
Phosphorus	P	1.0%	Component of bones and nucleic acids
Potassium	K	0.4%	Major cation in cells; needed for nerve function
Sulfur	S	0.3%	Component of proteins
Sodium	Na	0.2%	Major cation in extracellular fluid; needed for nerve function
Chlorine	Cl	0.2%	Major anion in extracellular fluid

Additional info:

• Understanding basic chemistry is essential for grasping physiological processes such as metabolism, cellular respiration, and molecular interactions in the human body.