Basic Chemistry Foundations for Anatomy & Physiology

Basic Chemistry Part I

Overview

Chemistry forms the foundation for understanding biological processes in Anatomy & Physiology. The study of the human body begins at the simplest level of organization: atoms and molecules. The types of atoms and the ways they combine to form molecules determine the characteristics of all substances in the body.

• Levels of Organization: Chemicals → Cells → Tissues → Organs → Organ Systems → Organism

• Atoms and Molecules: Atoms are the basic particles of matter; molecules are formed when atoms bond together.

Matter

Matter is anything that has mass and takes up space. All living and non-living things are composed of matter, which exists in three states: solid, liquid, and gas.

• Mass: The amount of matter in an object; does not change with location.

• Weight: The measurement of the pull of gravity on an object; changes with location (e.g., weightless in space).

• States of Matter:

  • Solid: Definite shape and volume

  • Liquid: Definite volume, shape of container

  • Gas: No definite shape or volume

Elements

Elements are pure substances that cannot be broken down into simpler substances by normal chemical reactions. All matter is composed of elements.

• Definition: An element is any substance that cannot be broken down into another substance by a chemical reaction.

• Examples: Carbon (C), Oxygen (O), Hydrogen (H)

• Periodic Table: Organizes all known elements by atomic number and properties.

Periodic Table of Elements

The periodic table lists 92 naturally-occurring elements and several synthetic ones. Each element is represented by a symbol, atomic number, and atomic weight.

• Atomic Number: Number of protons in the nucleus of an atom.

• Elemental Symbol: One or two letters representing the element (e.g., H for hydrogen, Na for sodium).

• Atomic Weight: Average mass of atoms of an element, measured in atomic mass units (amu).

Element	Symbol	Atomic Number	Atomic Weight
Carbon	C	6	12.01
Oxygen	O	8	16.00
Hydrogen	H	1	1.01
Sodium	Na	11	22.99
Calcium	Ca	20	40.08

Additional info: The periodic table is essential for understanding the chemical properties and interactions of elements in biological systems.

Atoms

An atom is the smallest unit of matter that retains the properties of an element. Atoms are composed of subatomic particles: protons, neutrons, and electrons.

• Protons (p): Positive charge, located in the nucleus

• Neutrons (n): Neutral charge, located in the nucleus

• Electrons (e): Negative charge, orbiting the nucleus in electron shells

Atomic Structure: The nucleus contains protons and neutrons; electrons move in shells around the nucleus.

Atomic Number and Atomic Mass

• Atomic Number: Number of protons in the nucleus; determines the identity of the element.

• Atomic Mass: Sum of protons and neutrons in the nucleus. $ext{Atomic Mass} = ext{Number of Protons} + ext{Number of Neutrons}$

Isotopes

• Isotopes: Atoms of the same element with different numbers of neutrons; same atomic number, different atomic mass.

• Radioactive Isotopes: Unstable isotopes that emit energy or particles; used in medical diagnostics (e.g., Technetium-99, Iodine-131).

Electron Shells and Valence Electrons

Electrons occupy energy levels called shells around the nucleus. The arrangement of electrons determines how atoms interact and bond.

• First Shell: Holds up to 2 electrons

• Second Shell: Holds up to 8 electrons

• Valence Shell: Outermost shell; electrons here are called valence electrons and determine chemical reactivity

Molecules and Compounds

Molecules are formed when two or more atoms bond together. Compounds are molecules that contain atoms of more than one element.

• Molecule: Two or more atoms bonded together (e.g., O2, H2)

• Compound: Molecule containing different elements (e.g., H2O, CO2)

• Key Point: All compounds are molecules, but not all molecules are compounds.

Chemical Bonds

Chemical bonds are forces that hold atoms together in molecules and compounds. The main types are ionic, covalent, and hydrogen bonds.

Ions, Cations, and Anions

• Ion: Atom or molecule with a net electric charge due to loss or gain of electrons

• Cation: Positively charged ion (loss of electrons)

• Anion: Negatively charged ion (gain of electrons)

Ionic Bonds

• Formed by the electrical attraction between cations and anions

• Result from the transfer of electrons from one atom to another

• Example: Sodium (Na) loses an electron to become Na+; Chlorine (Cl) gains an electron to become Cl-; Na+ and Cl- attract to form NaCl (table salt)

Covalent Bonds

• Formed when atoms share electrons in their valence shells

• Single covalent bond: sharing one pair of electrons

• Double covalent bond: sharing two pairs of electrons

• Polar Covalent Bond: Unequal sharing of electrons; creates polar molecules (e.g., water)

• Nonpolar Covalent Bond: Equal sharing of electrons

Hydrogen Bonds

• Weak attractions between a slightly positive hydrogen atom in one molecule and a slightly negative atom (oxygen or nitrogen) in another molecule

• Important in stabilizing the structure of proteins and DNA

Chemical Reactions

Chemical reactions involve the making or breaking of chemical bonds, resulting in new substances.

• Reactants: Starting substances in a reaction

• Products: Substances formed by the reaction

• General Equation: $ext{A} + ext{B} ightarrow ext{AB}$

Types of Chemical Reactions

• Decomposition Reaction: Breaks a molecule into smaller parts $ext{AB} ightarrow ext{A} + ext{B}$ Example: Hydrolysis in digestion

• Synthesis Reaction: Combines smaller molecules to form a larger one $ext{A} + ext{B} ightarrow ext{AB}$ Example: Dehydration synthesis in building proteins

• Reversible Reaction: Can proceed in both directions $ext{A} + ext{B} ightleftharpoons ext{AB}$

Enzymes and Activation Energy

Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy required. They are essential for life because they allow reactions to occur at body temperature and pH.

• Activation Energy: Minimum energy required to start a reaction

• Enzyme Function: Lower activation energy, accelerate reaction rate, remain unchanged after the reaction

• Catalyst: Substance that increases reaction rate without being consumed

Additional info: Enzymes are specific to the reactions they catalyze and are crucial for metabolic processes in cells.