Chapter 2: Basic Chemistry – Essentials of Human Anatomy & Physiology

Matter and Energy

Definition and States of Matter

Matter is defined as anything that occupies space and has mass. 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; takes the shape of its container.

• Gas: Neither definite shape nor volume.

Physical and Chemical Changes

Matter can undergo changes that are either physical or chemical:

• Physical changes: Do not alter the basic nature of a substance (e.g., change of state: solid, liquid, gas).

• Chemical changes: Alter the chemical composition of a substance, resulting in new substances.

Energy and Its Forms

Energy is the ability to do work and is fundamental to physiological processes.

• Kinetic energy: Energy in action, performing work.

• Potential energy: Stored energy, available for use.

Forms of Energy

• Chemical energy: Stored in chemical bonds of substances.

• Electrical energy: Results from movement of charged particles.

• Mechanical energy: Directly involved in moving matter.

• Radiant energy: Travels in waves; part of the electromagnetic spectrum.

Energy Conversion in the Body

• ATP (Adenosine Triphosphate): Traps chemical energy from food in its bonds, making it available for cellular work.

Composition of Matter

Elements and Their Biological Importance

Elements are the fundamental units of matter. The human body is primarily composed of four elements:

1. Oxygen (O): 65% of body mass; essential for cellular respiration.

2. Carbon (C): 18.5%; backbone of all organic molecules.

3. Hydrogen (H): 9.5%; found in water and most organic compounds.

4. Nitrogen (N): 3.2%; component of proteins and nucleic acids.

The periodic table lists all known elements, many of which play roles in physiology.

Table: Common Elements Making Up the Human Body

Element	Atomic Symbol	Percentage of Body Mass	Role
Oxygen	O	65.0	Major component of organic/inorganic molecules; essential for ATP production.
Carbon	C	18.5	Primary element in organic molecules.
Hydrogen	H	9.5	Component of all organic molecules.
Nitrogen	N	3.2	Component of proteins and nucleic acids.

Atoms and Subatomic Particles

Atoms are the building blocks of elements. Each atom consists of subatomic particles:

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

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

• Electrons (e-): Negatively charged, orbit the nucleus.

Table: Subatomic Particles

Particle	Position in Atom	Mass (amu)	Charge
Proton (p+)	Nucleus	1	+
Neutron (n0)	Nucleus	1	0
Electron (e-)	Orbits nucleus	1/2000*	-

*Electron mass is so small it is often considered 0 amu.

Atomic Models

Planetary and Orbital Models

Two models describe atomic structure:

• Planetary model: Atom as a miniature solar system; protons and neutrons in nucleus, electrons in orbitals.

• Orbital model: Electrons depicted as a cloud of negative charge outside the nucleus.

Electrons determine chemical behavior and bonding properties.

Identifying Elements

Atomic Number, Mass Number, and Weight

• Atomic number: Number of protons; unique to each element.

• Atomic mass number: Sum of protons and neutrons.

• Atomic weight: Approximate mass of the most abundant isotope.

Isotopes

Isotopes are atoms of the same element with different numbers of neutrons, resulting in different atomic masses.

Molecules and Compounds

Definitions and Examples

• Molecule: Two or more atoms of the same element combined chemically. Example: $H + H ightarrow H_2$

• Compound: Two or more atoms of different elements combined chemically. Example: $4H + C ightarrow CH_4$ (methane)

Properties of Compounds

Compounds have properties different from the individual elements that compose them (e.g., sodium chloride is table salt, but sodium and chlorine are hazardous alone).

Chemical Bonds and Chemical Reactions

Types of Chemical Bonds

• Ionic bonds: Formed by complete transfer of electrons from one atom to another, resulting in ions (anions and cations).

• Covalent bonds: Formed by sharing electrons between atoms; can be single or double bonds.

Role of Electrons in Bonding

• Electrons occupy energy levels (shells); only those in the outermost shell (valence shell) participate in bonding.

• Atoms are stable when their valence shell is full (usually 8 electrons, except for shell 1 which holds 2).

• Atoms with incomplete valence shells are chemically reactive.

Table: Chemically Inert and Reactive Elements

Element	Valence Electrons	Reactivity
Helium (He)	2	Inert
Neon (Ne)	8	Inert
Hydrogen (H)	1	Reactive
Carbon (C)	4	Reactive
Oxygen (O)	6	Reactive
Sodium (Na)	1	Reactive

Summary

This chapter provides foundational knowledge of basic chemistry as it applies to human anatomy and physiology, including the nature of matter and energy, atomic structure, chemical bonding, and the biological significance of elements and compounds.