Matter, Energy & Bonds: Foundations for Anatomy & Physiology

Matter, Energy & Bonds

Introduction

Understanding the basic principles of matter, energy, and chemical bonds is essential for studying Anatomy & Physiology. These concepts explain the structure and behavior of atoms and molecules, which form the basis of all biological processes in the human body.

Subatomic Particles and Atomic Structure

Electrons, Protons & Neutrons

Atoms are composed of three fundamental subatomic particles: protons, neutrons, and electrons. Their arrangement and properties determine the identity and behavior of each atom.

• Protons: Positively charged particles located in the nucleus; each has a mass of 1 atomic mass unit (AMU).

• Neutrons: Neutral particles also found in the nucleus; mass is 1 AMU.

• Electrons: Negatively charged particles found in orbitals around the nucleus; mass is negligible (~0 AMU).

Summary Table: Subatomic Particles

Particle Name	Location	Charge	Mass
Electron	Orbitals	-1	~0
Proton	Nucleus	+1	1
Neutron	Nucleus	No Charge	1

Atomic Number vs. Mass Number

• Atomic Number: The number of protons in the nucleus; defines the element.

• Mass Number: The sum of protons and neutrons in the nucleus.

Formula:

$\text{Atomic Mass} = n(\text{Protons}) + n(\text{Neutrons})$

Atoms are usually electrically neutral, meaning the number of protons equals the number of electrons.

Electron Shells and the Octet Rule

Electrons occupy specific energy levels called electron shells around the nucleus. The arrangement of electrons in these shells determines the atom's chemical properties.

• 1st shell: Holds up to 2 electrons.

• 2nd shell: Holds up to 8 electrons.

• 3rd shell: Holds up to 8 electrons ("satisfied" with 8; Octet Rule).

• Atoms may have more than three shells.

The Octet Rule states that atoms are most stable when their outermost shell contains 8 electrons.

Atoms, Elements, and Major Elements in the Body

Atoms vs. Elements

An atom is the smallest unit of matter that retains the properties of an element. An element is a pure substance made up of only one kind of atom.

• Each element has unique chemical properties.

• Examples: Hydrogen and Oxygen are elements; a water molecule (H2O) is a compound made of these elements.

Major Elements in the Human Body

• Oxygen (O)

• Carbon (C)

• Hydrogen (H)

• Nitrogen (N)

These four elements make up over 96% of the human body's mass.

Isotopes and Radioisotopes

Definitions and Properties

Isotopes are atoms of the same element that differ in the number of neutrons, resulting in different mass numbers. Radioisotopes are unstable isotopes that decay over time, emitting radiation.

• Isotopes have identical chemical behavior but may differ physically.

• Radioisotopes undergo radioactive decay, releasing alpha, beta, or gamma radiation.

Example: Hydrogen has three isotopes: Protium (1 proton), Deuterium (1 proton, 1 neutron), and Tritium (1 proton, 2 neutrons; radioactive).

Applications of Radioisotopes

• Medical Imaging: Radioisotopes are used as tracers to visualize organ function.

• Radiation Therapy: Used to treat cancer by damaging cancerous cells.

• Diagnosis: Examples include Gallium-67, Iodine-123, and Iodine-125 for thyroid and metabolic disorders.

Mixtures: Solutions, Colloids, and Suspensions

Definitions and Differences

Mixtures are combinations of two or more substances that are physically blended but not chemically bonded.

• Solution: Homogeneous mixture with very small, evenly distributed particles; solute is dissolved in solvent (e.g., salt water).

• Colloid: Mixture with small, evenly distributed particles that do not settle out (e.g., milk).

• Suspension: Heterogeneous mixture with large, unevenly distributed particles that settle out when left undisturbed (e.g., blood cells in plasma).

Solute: Substance dissolved. Solvent: Substance that dissolves the solute (often water in biological systems).

Valence Shells and Chemical Reactivity

Role of Valence Electrons

The valence shell is the outermost electron shell of an atom. The number of electrons in this shell determines the atom's chemical reactivity.

• Atoms with full valence shells are chemically inert (stable).

• Atoms with incomplete valence shells are chemically reactive and tend to form bonds to achieve stability (Octet or Duet Rule).

Ions and Electrolytes

Definitions and Biological Importance

Ions are charged particles formed when atoms gain or lose electrons. Electrolytes are substances that dissociate into ions in water and can conduct electricity.

• Cation: Positively charged ion (loss of electrons).

• Anion: Negatively charged ion (gain of electrons).

• Electrolytes are essential for nerve impulse transmission, muscle contraction, and maintaining fluid balance.

Chemical Bonds: Types and Biological Examples

Overview of Chemical Bonds

Chemical bonds are forces that hold atoms together in molecules and compounds. The type of bond depends on how valence electrons are distributed.

• Ionic Bonds: Formed by the transfer of electrons from one atom to another, resulting in oppositely charged ions that attract each other (e.g., NaCl).

• Non-polar Covalent Bonds: Electrons are shared equally between atoms (e.g., O2 molecule).

• Polar Covalent Bonds: Electrons are shared unequally, creating partial charges (e.g., H2O).

• Hydrogen Bonds: Weak attractions between polar molecules, often involving hydrogen (e.g., between water molecules, within proteins and DNA).

• Van der Waals Forces: Weak attractions due to temporary polarization in nonpolar molecules.

Comparison Table: Types of Chemical Bonds

Bond Type	Mechanism	Strength	Biological Example
Ionic	Transfer of electrons	Strong (in dry state)	NaCl (table salt)
Non-polar Covalent	Equal sharing of electrons	Strongest	O2 molecule
Polar Covalent	Unequal sharing of electrons	Strong	H2O (water)
Hydrogen	Attraction between polar molecules	Weak	Between water molecules, DNA strands
Van der Waals	Temporary polarization	Very weak	Lipid interactions

Example: Water (H2O) is held together by polar covalent bonds, and water molecules interact via hydrogen bonds.

Additional info: Academic context and examples have been expanded for clarity and completeness.