Basic Chemistry for Anatomy & Physiology: Matter, Energy, and Chemical Reactions

Part 1: Basic Chemistry

Definition of Concepts: Matter and Energy

This section introduces the foundational concepts of matter and energy, which are essential for understanding chemical processes in the human body.

• Matter: Anything that occupies space and has mass. Matter exists in solid, liquid, and gaseous states.

• Energy: The capacity to do work or put matter into motion. The greater the work being performed, the more energy is used in doing it.

Energy exists in two states:

• Kinetic Energy: The energy of motion or movement (energy in action).

• Potential Energy: Stored energy, which has the potential to do work but is not currently active.

Major Forms of Energy

• Chemical Energy: Energy stored in the bonds of chemical substances. When these bonds are rearranged during chemical reactions, the stored potential energy is released and transformed into kinetic energy, which can then be used to perform work.

• Electrical Energy: Energy resulting from the movement of charged particles. In the human body, electrical energy is crucial for various functions, such as nerve impulse transmission, generated when ions move across cell membranes.

• Mechanical Energy: Energy directly involved in moving matter. For example, when you ride a bicycle, your legs provide the mechanical energy that moves the pedals.

• Radiant Energy: (Electromagnetic radiation) Energy that travels in waves, such as visible light, ultraviolet waves, and X-rays. Note: This topic may not be covered in detail.

Elements, Atoms, and Atomic Structure

Chemical Elements

A chemical element is a unique substance that cannot be broken down into simpler substances by ordinary chemical methods. The four elements that form the bulk of body matter are:

• Carbon (C)

• Oxygen (O)

• Hydrogen (H)

• Nitrogen (N)

Atomic Structure

• Atom: The smallest particle of an element that retains the properties of that element. Atoms are composed of three main subatomic particles:

  • Protons: Positively charged particles located in the nucleus. Mass = 1 atomic mass unit (AMU).

  • Neutrons: Neutral particles found in the nucleus. Mass = 1 AMU.

  • Electrons: Negatively charged particles that orbit the nucleus in electron shells. Negligible mass (0.0005 AMU).

Atomic Number, Atomic Mass, Isotopes, and Radioisotopes

• Atomic Number: The number of protons in an atom's nucleus. It defines the element.

• Atomic Mass: The sum of protons and neutrons in the nucleus. For example, carbon-12 has 6 protons and 6 neutrons, so its atomic mass is 12 AMU.

• Isotopes: Atoms of the same element with different numbers of neutrons. Isotopes have identical chemical properties but different atomic masses.

• Radioisotopes: Isotopes that are unstable and undergo spontaneous decay, emitting radiation. This process is known as radioactivity and involves the emission of alpha particles, beta particles, or gamma rays.

How Matter is Combined: Molecules and Mixtures

Molecules and Compounds

• Molecule: A particle consisting of two or more atoms joined together by chemical bonds. If the atoms are of the same element, the molecule is called a molecule of that element (e.g., O2).

• Compound: A substance composed of two or more different elements, chemically combined (e.g., H2O).

Mixtures

• Mixture: A physical combination of two or more substances. No chemical bonding occurs between the components. Types of mixtures include:

  • Solutions: Homogeneous mixtures with uniform composition (e.g., salt water).

  • Colloids: Heterogeneous mixtures with particles that do not settle out (e.g., cytosol in cells).

  • Suspensions: Heterogeneous mixtures with large, often visible solutes that tend to settle out (e.g., blood).

Distinguishing Compounds and Mixtures

• Mixtures: Components can be separated by physical means (straining, filtering, evaporation). Properties of components remain unchanged. Can be homogeneous or heterogeneous.

• Compounds: Components can only be separated by chemical means (breaking bonds). Always homogeneous, with elements uniformly bonded.

Chemical Bonding

Role of Electrons in Chemical Bonding

Electrons occupy regions called electron shells around an atom's nucleus. The outermost shell is the valence shell, and electrons here are most involved in chemical bonding.

Types of Chemical Bonds

• Ionic Bonds: Formed when electrons are completely transferred from one atom to another, resulting in charged ions (e.g., NaCl).

• Covalent Bonds: Formed when atoms share electron pairs. If shared equally, the bond is nonpolar (e.g., CO2); if shared unequally, it is polar (e.g., H2O).

• Hydrogen Bonds: Weak bonds between a hydrogen atom (already covalently linked to an electronegative atom) and another electronegative atom.

Polar vs. Nonpolar Molecules

• Nonpolar Molecules: Electrically symmetrical; electrons are shared equally, resulting in no distinct positive or negative poles.

• Polar Molecules: Electrically asymmetrical; electrons are shared unequally, resulting in partial positive and negative charges (e.g., water).

Chemical Reactions

Types of Chemical Reactions

• Synthesis Reaction: Involves bond formation. Two or more substances combine to form a more complex product. General equation: $A + B \rightarrow AB$

• Decomposition Reaction: A molecule is broken down into smaller molecules or constituent atoms. General equation: $AB \rightarrow A + B$

• Exchange Reaction: Involves both synthesis and decomposition; bonds are both made and broken. General equation: $AB + CD \rightarrow AD + CB$

Irreversibility of Chemical Reactions in the Body

• Energy Release: Many biological reactions release energy, making the reverse reaction impractical.

• Product Removal: If a product is continuously removed (e.g., CO2 exhaled from the lungs), the reverse reaction cannot occur.

Factors Affecting Chemical Reaction Rates

• Temperature: Higher temperatures increase kinetic energy, leading to more frequent and forceful collisions, thus increasing reaction rates.

• Concentration: Higher concentrations of reactants increase the probability of successful collisions, accelerating the reaction.

• Particle Size: Smaller particles move faster and collide more frequently and forcefully, resulting in faster reaction rates.

Summary Table: Types of Chemical Reactions

Type	Description	General Equation	Example
Synthesis	Bond formation; two or more substances combine	$A + B \rightarrow AB$	Amino acids join to form a protein molecule
Decomposition	Breaking down of a molecule into smaller parts	$AB \rightarrow A + B$	Glycogen broken down to release glucose units
Exchange	Bonds are both made and broken; atoms are exchanged	$AB + CD \rightarrow AD + CB$	ATP transfers phosphate group to glucose

Additional info: These notes provide a concise overview of basic chemistry concepts relevant to Anatomy & Physiology, including matter, energy, atomic structure, chemical bonding, and types of chemical reactions. Understanding these principles is essential for further study of physiological processes.