Introduction to the Chemical Level of Organization

Overview

This chapter introduces the foundational concepts of chemistry as they apply to anatomy and physiology. Understanding the chemical basis of life is essential for comprehending how biological processes occur at the molecular level.

• Purpose: To introduce the language and fundamental concepts of chemistry.

• Discuss how matter is organized.

• Explain how chemical bonds form and how chemical reactions occur.

• Compare and contrast organic and inorganic compounds.

How Matter is Organized

States of Matter

Matter is anything that has mass and occupies space. In biological systems, matter exists in three primary forms:

• Solid: Has definite shape and volume.

• Liquid: Has definite volume but takes the shape of its container.

• Gas: Has neither definite shape nor volume.

All forms of matter are composed of chemical elements.

Chemical Elements

Major and Minor Elements in the Body

Chemical elements are substances that cannot be broken down into simpler substances by ordinary chemical means. Each element is represented by a unique chemical symbol.

• O = oxygen

• C = carbon

• H = hydrogen

• N = nitrogen

These elements make up the majority of the human body. Other important elements include:

• Na = sodium

• K = potassium

• Ca = calcium

• Cl = chloride

• Fe = iron

Atoms

Structure and Properties

Atoms are the smallest units of matter that retain the properties and characteristics of an element. All chemical elements are composed of atoms.

• Protons (p+): Positively charged particles located in the nucleus.

• Neutrons (n0): Neutral particles located in the nucleus.

• Electrons (e-): Negatively charged particles that orbit the nucleus in shells.

Atoms are represented by models such as the electron cloud model and the electron shell model.

Atomic Number and Mass Number

Definitions and Calculations

Atoms are identified by their chemical symbol, atomic number, and mass number.

• Atomic number: The number of protons in the nucleus of an atom. In a neutral atom, this is also equal to the number of electrons.

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

Example: For Carbon (C):

• Atomic number = 6

• Mass number = 12

• Number of neutrons = 12 - 6 = 6

Atomic Structure of Elements

Electron Configuration

The arrangement of electrons in shells around the nucleus determines the chemical properties of an element.

• Protons and neutrons are present in the nucleus.

• Electrons are present in shells around the nucleus.

• Shells fill from inside to outside as atomic number increases.

• Each shell can hold a maximum number of electrons:

  • Shell 1: Maximum of 2 electrons

  • Shell 2: Maximum of 8 electrons

  • Shell 3: Maximum of 8 electrons

• The outermost shell is called the valence shell.

Example: Carbon (C) has 6 electrons: 2 in the first shell, 4 in the second shell.

Chemical Bonds

Formation and Types

A chemical bond occurs when atoms are held together by forces of attraction. The number of electrons in the valence shell determines the likelihood that an atom will form a chemical bond with another atom. Atoms are most stable when their valence shell is full.

• Ionic Bonds: Formed when one atom transfers electrons to another, resulting in the formation of ions (charged particles).

• Covalent Bonds: Formed when atoms share electrons. Can be single, double, or triple bonds depending on the number of electron pairs shared.

• Hydrogen Bonds: Result from the attraction of oppositely charged parts of molecules, especially in water. These bonds create surface tension.

Example: Carbon (C) forms covalent bonds by sharing electrons to fill its valence shell.

Summary Table: Major Elements and Their Atomic Structure

Key Terms and Concepts

• Atom: The smallest unit of an element that retains its properties.

• Element: A pure substance made of only one kind of atom.

• Proton: Positively charged particle in the nucleus.

• Neutron: Neutral particle in the nucleus.

• Electron: Negatively charged particle orbiting the nucleus.

• Valence Shell: The outermost electron shell of an atom.

• Chemical Bond: The force that holds atoms together in molecules.

Equations and Formulas

• Number of Neutrons:

Summary

This chapter provides the chemical foundation necessary for understanding biological processes in anatomy and physiology. Mastery of these concepts is essential for further study of cellular and molecular mechanisms in the human body.