Basic Chemistry

Introduction

Chemistry is fundamental to understanding anatomy and physiology, as all body processes are based on chemical interactions. This section covers the essential chemical principles relevant to biological systems, including matter, energy, atomic structure, chemical bonds, and types of chemical reactions.

Matter and Energy

Definitions and Properties

• Matter: Anything that has mass and occupies space. Matter can be seen, smelled, and/or felt.

• Weight: The effect of gravity on mass.

States of Matter

• Solid: Definite shape and volume.

• Liquid: Changeable shape, definite volume.

• Gas: Changeable shape and volume.

Energy

• Energy: The capacity to do work or put matter into motion.

• Energy does not have mass or take up space.

• The greater the work done, the more energy it uses up.

Forms of Energy

• Kinetic Energy: Energy in action (e.g., movement of muscles).

• Potential Energy: Stored energy (e.g., energy stored in chemical bonds).

Types of Energy in the Body

• Chemical Energy: Stored in bonds of chemical substances.

• Electrical Energy: Results from movement of charged particles.

• Mechanical Energy: Directly involved in moving matter.

• Radiant/Electromagnetic Energy: Travels in waves (e.g., light).

Energy Conversions

• Energy may be converted from one form to another (e.g., chemical energy in food converted to kinetic energy for movement).

• Some energy is always lost as heat during conversions, making it unusable.

Atoms and Elements

Atoms and Elements Overview

• Element: A pure substance that cannot be broken down by ordinary chemical means.

• Four elements make up 96% of the human body: Carbon (C), Oxygen (O), Hydrogen (H), Nitrogen (N).

• Other elements are present in smaller amounts.

• The periodic table lists all known elements.

Atomic Structure

• Atoms are composed of subatomic particles:

  • Protons: Positive charge, mass = 1 amu, located in nucleus.

  • Neutrons: No charge, mass = 1 amu, located in nucleus.

  • Electrons: Negative charge, negligible mass, orbit nucleus in electron shells.

• The number of protons equals the number of electrons in a neutral atom.

• The planetary model shows electrons in orbits around the nucleus.

Identifying Elements

• Each element is identified by:

  • Atomic Number: Number of protons in the nucleus.

  • Mass Number: Total number of protons and neutrons.

  • Isotopes: Atoms with the same number of protons but different numbers of neutrons.

  • Atomic Weight: Average mass of all isotopes of an element.

• Radioisotopes: Unstable isotopes that decompose to more stable forms, sometimes emitting radiation.

Atomic Symbols

• Each element is represented by a one- or two-letter symbol (e.g., O for oxygen, C for carbon).

• Some symbols are derived from Latin names (e.g., Na for sodium, K for potassium).

Combining Matter: Molecules and Compounds

Molecules and Compounds

• Molecule: Two or more atoms bonded together (e.g., O2).

• Compound: Two or more different kinds of atoms bonded together (e.g., H2O).

Mixtures

• Most matter exists as mixtures: two or more components physically intermixed.

• Three basic types of mixtures:

  1. Solutions: Homogeneous mixtures; solute particles are very tiny and do not settle out or scatter light (e.g., saline solution).

  2. Colloids: Heterogeneous mixtures; solute particles are larger than in solutions and scatter light, but do not settle out (e.g., cytosol).

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

Solution Terminology

• Solvent: Substance present in greatest amount (usually water in the body).

• Solute: Substance dissolved in solvent (e.g., glucose in blood plasma).

Concentration of Solutions

• Common ways to express concentration:

  1. Percent (parts solute per 100 parts solvent).

  2. Milligrams per deciliter (mg/dL).

  3. Molarity (moles of solute per liter of solution).

• 1 mole of any substance contains Avogadro's number of molecules: .

Chemical Bonds

Types of Chemical Bonds

• Ionic Bonds: Formed by transfer of electrons from one atom to another, resulting in ions (cations and anions) that are attracted to each other.

• Covalent Bonds: Formed by sharing of two or more valence electrons between atoms.

• Hydrogen Bonds: Weak attractions between a hydrogen atom and an electronegative atom (e.g., oxygen or nitrogen).

Ionic Bonds

• One atom becomes an anion (gains electrons, negative charge).

• One atom becomes a cation (loses electrons, positive charge).

• Attraction of opposite charges forms the ionic bond.

Covalent Bonds

• Atoms share electrons to fill their valence shells.

• Can be single, double, or triple bonds depending on the number of shared electron pairs.

• Nonpolar covalent bonds: Electrons shared equally (e.g., O2).

• Polar covalent bonds: Electrons shared unequally, resulting in partial charges (e.g., H2O).

Hydrogen Bonds

• Attractive force between a hydrogen atom (already covalently bonded to an electronegative atom) and another electronegative atom.

• Important in water, proteins, and nucleic acids.

Chemical Reactions

Types of Chemical Reactions

• Synthesis (Combination) Reactions: Atoms or molecules combine to form a larger, more complex molecule. Used in anabolic (building) processes.

• Decomposition Reactions: Breakdown of a molecule into smaller molecules or atoms. Used in catabolic (bond-breaking) processes.

• Exchange (Displacement) Reactions: Involve both synthesis and decomposition; bonds are both made and broken.

Redox (Oxidation-Reduction) Reactions

• Atoms are reduced when they gain electrons and oxidized when they lose electrons.

• All chemical reactions are either exergonic (release energy) or endergonic (absorb energy).

Chemical Equations

• Chemical reactions can be written as equations showing reactants and products.

• Balanced equations show the same number of each type of atom on both sides.

• Compounds are represented by molecular formulas (e.g., H2O, C6H12O6).

Summary Table: Types of Chemical Bonds

Additional Info

• Atoms strive for stability by filling their outermost electron shell (octet rule).

• Electrons in the valence shell are most involved in chemical bonding.

• Radioisotopes can be used in medical imaging and cancer treatment, but may also pose health risks.