Chapter 2: The Chemical Level of Organization – Study Notes

The Chemical Level of Organization

Introduction to the Chemical Level

The chemical level of organization is foundational to understanding anatomy and physiology. Chemistry is the science that deals with the structure of matter, including the structure of atoms, basic chemical building blocks, and how atoms combine to form increasingly complex structures.

• Chemistry: The study of matter and its interactions.

• Structure of atoms: Atoms are the basic units of matter.

• Complex structures: Atoms combine to form molecules and compounds essential for physiological processes.

Atoms and Atomic Structure

Matter and Atoms

Matter is anything that takes up space and has mass. All matter is composed of atoms, which join together to form chemicals with distinct characteristics. These chemical characteristics determine physiological functions at the molecular and cellular levels.

• Matter: Anything with mass and volume.

• Atoms: The smallest units of matter, forming chemicals.

• Chemical characteristics: Influence physiology and cellular function.

Subatomic Particles

Atoms are made up of three main subatomic particles:

• Protons: Positively charged, 1 mass unit.

• Neutrons: Neutral charge, 1 mass unit.

• Electrons: Negatively charged, very low mass.

Atomic Structure

The structure of an atom consists of a nucleus and an electron cloud. The atomic number is determined by the number of protons in the nucleus.

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

• Nucleus: Contains protons and neutrons.

• Electron cloud: Spherical area containing electrons.

• Electron shell: A two-dimensional representation of the electron cloud.

Principal Elements in the Human Body

Several elements are essential for human physiology. The following tables summarize their significance:

Element	% of Total Body Weight	Significance
O (Oxygen)	65.0	Component of water and other compounds; essential for respiration.
C (Carbon)	18.6	Found in all organic molecules.
H (Hydrogen)	9.7	Component of water and most compounds in the body.
N (Nitrogen)	3.2	Found in proteins, nucleic acids, and other organic compounds.
Ca (Calcium)	1.8	Important for bones, teeth, membrane function, nerve impulses, muscle contraction, and blood clotting.
P (Phosphorus)	1.0	Found in bones, teeth, nucleic acids, and high-energy compounds.
K (Potassium)	0.4	Important for membrane function, nerve impulses, and muscle contraction.

Element	% of Total Body Weight	Significance
Na (Sodium)	0.2	Important for blood volume, membrane function, nerve impulses, and muscle contraction.
Cl (Chlorine)	0.2	Important for blood volume, membrane function, and water absorption.
Mg (Magnesium)	0.06	Cofactor for many enzymes.
S (Sulfur)	0.04	Found in many proteins.
Fe (Iron)	0.007	Essential for oxygen transport and energy capture.
I (Iodine)	0.002	Component of hormones of the thyroid gland.
Trace elements	<0.01	Some function as cofactors; functions of many trace elements are poorly understood.

Isotopes and Atomic Mass

An element is a pure substance composed of atoms of only one kind. The atomic number (number of protons) determines its chemical properties. Isotopes are versions of elements with different mass numbers, which is the sum of protons and neutrons.

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

• Mass number: $\text{Mass number} = \text{Number of protons} + \text{Number of neutrons}$

Example: Hydrogen has three isotopes: Hydrogen-1 (1 proton), Deuterium (1 proton, 1 neutron), Tritium (1 proton, 2 neutrons).

Electrons and Energy Levels

Electrons in the electron cloud determine the reactivity of an atom. The cloud contains shells, or energy levels, that can hold a limited number of electrons. Lower shells fill first, and the outermost shell (valence shell) determines bonding.

• Valence shell: Outermost electron shell; determines chemical bonding.

• Electron configuration: Influences how atoms interact and form molecules.

Additional info: Atoms are most stable when their valence shell is full, leading to chemical bonding through electron sharing, gaining, or losing.