Atoms, Elements, Chemical Bonds, and Water: Foundations for Anatomy & Physiology

Module 2.1: Atoms and Elements

Definition of Matter

Matter is anything that has mass and occupies space, existing as solid, liquid, or gas. Chemistry is the study of matter and its interactions.

• Matter includes all substances that make up the physical world.

• States of matter: solid, liquid, gas.

Atoms and Atomic Structure

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

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

• Neutrons (n0): No charge, also found in the nucleus.

• Electrons (e-): Negatively charged, found outside the nucleus in electron shells.

• Atoms are electrically neutral when the number of protons equals the number of electrons.

Electron Shells

Electrons occupy regions called electron shells around the nucleus.

• First shell: holds up to 2 electrons.

• Second shell: holds up to 8 electrons.

• Third shell: can hold up to 18 electrons, but is stable with 8.

Elements and the Periodic Table

An element is a substance that cannot be broken down by chemical means. Each element is defined by its atomic number (number of protons).

• The periodic table organizes elements by atomic number and properties.

• Major elements in the human body: hydrogen, oxygen, carbon, nitrogen.

• Minor elements: minerals and trace elements.

Isotopes and Radioactivity

Isotopes are atoms of the same element with different numbers of neutrons. Radioisotopes are unstable isotopes that emit radiation.

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

• Radioactive decay allows unstable isotopes to become more stable.

Module 2.2: Matter Combined: Mixtures and Chemical Bonds

Mixtures

A mixture is a combination of two or more substances physically intermixed without chemical bonding.

• Suspensions: Large particles, settle out (e.g., blood).

• Colloids: Smaller particles, do not settle out (e.g., cytosol).

• Solutions: Smallest particles, evenly distributed (e.g., salt water).

Type	Particle Size	Settling	Example
Suspension	Large	Settles	Blood
Colloid	Medium	No	Cytosol
Solution	Small	No	Salt water

Chemical Bonds

Chemical bonds are attractive forces holding atoms together in molecules and compounds.

• Molecule: Two or more atoms of the same element bonded together.

• Compound: Two or more atoms of different elements bonded together.

• Macromolecules: Large molecules composed of many atoms.

Valence Electrons and the Octet Rule

Valence electrons are electrons in the outermost shell, determining chemical reactivity.

• Octet rule: Atoms are most stable with eight electrons in their valence shell.

Ions and Ionic Bonds

Ionic bonds form when electrons are transferred from one atom to another, creating ions.

• Cation: Positively charged ion (loss of electrons).

• Anion: Negatively charged ion (gain of electrons).

• Ionic bonds result in the formation of salts.

Covalent Bonds

Covalent bonds form when atoms share electrons. Can be single, double, or triple bonds.

• Electronegativity: Ability of an atom to attract electrons.

• Polar covalent bonds: Unequal sharing of electrons (e.g., water).

• Nonpolar covalent bonds: Equal sharing of electrons (e.g., oxygen gas).

Hydrogen Bonds and Surface Tension

Hydrogen bonds are weak attractions between partially positive hydrogen and partially negative atoms (e.g., oxygen, nitrogen).

• Responsible for water's surface tension.

Module 2.3: Chemical Reactions

Chemical Notation

Chemical equations use symbols to represent reactions.

• Reactants: Starting substances.

• Products: Substances formed.

• Reversible reactions: Indicated by double arrows ($A + B \rightleftharpoons AB$).

Energy in Chemical Reactions

Chemical reactions involve energy changes.

• Potential energy: Stored energy.

• Kinetic energy: Energy of motion.

• Chemical energy: Stored in chemical bonds.

• Electrical energy: Movement of charged particles.

Types of Chemical Reactions

• Catabolic (decomposition) reactions: Break down molecules ($AB \rightarrow A + B$).

• Anabolic (synthesis) reactions: Build larger molecules ($A + B \rightarrow AB$).

• Exchange reactions: Swap components ($AB + CD \rightarrow AD + BC$).

• Oxidation-reduction (redox) reactions: Transfer electrons between atoms.

Reaction Rates and Enzymes

Reaction rates depend on concentration, temperature, particle size, and catalysts.

• Enzymes: Biological catalysts that speed up reactions by lowering activation energy.

• Enzymes are specific to substrates and are not consumed in reactions.

Module 2.4: Inorganic Compounds: Water, Acids, Bases, and Salts

Water

Water is essential for life and has unique properties due to its polar covalent bonds and hydrogen bonding.

• High heat capacity: Absorbs heat without changing temperature quickly.

• High heat of vaporization: Requires much energy to change from liquid to gas.

• Acts as a lubricant and cushion.

• Acts as a solvent for many substances.

Solubility and Hydrophilic/Hydrophobic Substances

• Hydrophilic: Substances that dissolve in water (ionic and polar molecules).

• Hydrophobic: Substances that do not dissolve in water (nonpolar molecules).

Acids and Bases

Acids and bases are defined by their behavior in water.

• Acid: Hydrogen ion donor ($H^+$).

• Base: Hydrogen ion acceptor ($OH^-$).

• Acids increase $H^+$ concentration; bases decrease $H^+$ concentration.

Salts

Salts are ionic compounds formed from the reaction of acids and bases. They dissociate in water to release ions.

Inorganic vs. Organic Compounds

• Inorganic compounds: Do not contain both carbon and hydrogen (e.g., water, salts).

• Organic compounds: Contain both carbon and hydrogen (e.g., carbohydrates, lipids, proteins, nucleic acids).

Key Terms and Concepts

• Atom: Smallest unit of matter.

• Element: Substance made of one type of atom.

• Isotope: Atom with same number of protons, different number of neutrons.

• Ionic bond: Transfer of electrons.

• Covalent bond: Sharing of electrons.

• Hydrogen bond: Weak attraction between polar molecules.

• Enzyme: Protein catalyst in biological reactions.

• Acid: Proton donor.

• Base: Proton acceptor.

• Salt: Ionic compound from acid-base reaction.

Example: Water ($H_2O$) is a polar molecule with hydrogen bonds, making it an excellent solvent and vital for physiological processes.

Additional info: These notes expand on the outline by providing definitions, examples, and context for key concepts in chemistry relevant to anatomy and physiology. All equations are provided in LaTeX format as required.