The Chemical Level of Organization: Foundations for Anatomy & Physiology

The Chemical Level of Organization

Introduction

The chemical level of organization is the foundation of anatomy and physiology, focusing on the elements, atoms, and chemical bonds that make up all living matter. Understanding these basics is essential for grasping how the human body functions at the molecular level.

Learning Objectives

• Understand what elements and atoms are, as well as what they are made up of.

• Understand how different chemical bonds work.

• Identify important inorganic compounds in humans.

• Identify important organic compounds in humans.

Overview of the Chemical Level of Organization

Basic Concepts

• The smallest, most fundamental material components of the human body are basic chemical elements.

• Human chemistry includes both organic compounds (carbon-based, produced by the body) and inorganic compounds (from the environment).

• Elements can form both inorganic and organic chemical compounds important to biological life (e.g., water, glucose, proteins).

Elements and Atoms

Definition of Matter and Elements

• Matter is anything that takes up space and has mass.

• All living things are formed of matter.

• An element is a substance that cannot be broken down into simpler substances by chemical reactions.

• Elements are made up of atoms.

Periodic Table and Elements in the Human Body

• The periodic table organizes elements by their properties.

• The human body is composed of several key elements, including carbon, hydrogen, oxygen, nitrogen, calcium, and phosphorus.

• Some elements must be obtained from the environment, as the body cannot synthesize them.

Major Elements in the Human Body

Element	Symbol	Approximate % of Body Weight
Oxygen	O	65%
Carbon	C	18%
Hydrogen	H	10%
Nitrogen	N	3%
Calcium	Ca	1.5%
Phosphorus	P	1%
Other elements	Various	Trace

Atoms: Structure and Properties

• An atom is the smallest quantity of an element that retains its unique properties.

• Atoms are made up of subatomic particles: protons (positive charge), neutrons (neutral), and electrons (negative charge).

• The number of protons determines the element's identity (atomic number).

• The number of neutrons plus protons gives the mass number.

Atomic Number and Mass Number

• Atomic number (Z): Number of protons in the nucleus.

• Mass number (A): Number of protons plus neutrons.

$\text{Atomic Number} = \text{Number of Protons}$ $\text{Mass Number} = \text{Number of Protons} + \text{Number of Neutrons}$

Calculating Neutrons

• Number of neutrons = Mass number - Atomic number

$\text{Number of Neutrons} = \text{Mass Number} - \text{Atomic Number}$

Isotopes

• Atoms of the same element with different numbers of neutrons are called isotopes.

• Isotopes have the same chemical properties but different physical properties (e.g., mass).

Electron Behaviour

Electron Shells and Energy Levels

• Electrons are located in energy levels (shells) around the nucleus.

• The energy level of an electron is correlated with its distance from the nucleus.

• Electrons tend to fill the lowest available energy levels first.

• The first shell can hold up to 2 electrons; higher shells can hold more.

Valence Electrons and Chemical Reactivity

• The outermost electrons are called valence electrons.

• The outer electron shell is called the valence shell.

• If the valence shell is full, the atom is unreactive (inert).

• If the valence shell is incomplete, the atom is reactive and can form chemical bonds.

Chemical Bonds

Overview

• Atoms combine to form molecules through chemical bonds.

• Chemical bonds are attractions between atoms that allow them to achieve stable electron configurations.

Covalent Bonds

• Covalent bonds are formed by the sharing of electrons between atoms.

• These are the strongest types of chemical bonds.

• When electrons are shared equally, the molecule is nonpolar; when shared unequally, the molecule is polar.

Polar vs. Nonpolar Covalent Bonds

• Nonpolar covalent bond: Electrons are shared equally.

• Polar covalent bond: Electrons are shared unequally, creating regions of partial positive and negative charge.

• Example: Water (H2O) is a polar molecule.

Hydrogen Bonds

• Hydrogen bonds are weak attractions between a hydrogen atom (attached to a highly electronegative atom like oxygen or nitrogen) and another electronegative atom.

• Hydrogen bonds are important in stabilizing the structure of water and biological molecules like DNA and proteins.

• Hydrogen bonding gives water its unique properties, such as high surface tension and boiling point.

Ionic Bonds

• Ionic bonds are formed when electrons are transferred from one atom to another, resulting in charged ions.

• A positively charged ion is called a cation; a negatively charged ion is called an anion.

• Oppositely charged ions attract each other to form ionic bonds.

• Compounds formed by ionic bonds are called ionic compounds (e.g., salts).

Properties of Ionic Compounds

• Ionic compounds form crystals with a definite size and number of atoms.

• Salts are found in nature as crystals of various sizes and shapes.

Chemical Reactions

Definition and Examples

• Chemical reactions involve the formation and breaking of chemical bonds, resulting in changes to the composition of matter.

• Reactants are the starting materials; products are the results of the reaction.

• Example: Formation of water from hydrogen and oxygen.

$2H_2 + O_2 \rightarrow 2H_2O$

Summary Table: Types of Chemical Bonds

Bond Type	Mechanism	Strength	Example
Covalent	Sharing of electrons	Strongest	Water (H2O)
Ionic	Transfer of electrons	Strong	Sodium chloride (NaCl)
Hydrogen	Attraction between polar molecules	Weak	Between water molecules

Key Terms

• Element: Pure substance made of only one kind of atom.

• Atom: Smallest unit of an element retaining its properties.

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

• Cation: Positively charged ion.

• Anion: Negatively charged ion.

• Covalent bond: Bond formed by sharing electrons.

• Ionic bond: Bond formed by transfer of electrons.

• Hydrogen bond: Weak bond between polar molecules.

• Reactant: Starting material in a chemical reaction.

• Product: Result of a chemical reaction.

Additional info: This guide expands on the original notes by providing definitions, examples, and context for each concept, ensuring a comprehensive understanding suitable for college-level Anatomy & Physiology students.