Chapter 2: The Chemistry of Life

Objectives

• Atomic Structure: Describe an atom and how atomic structure affects interactions between atoms.

• Formation of Molecules and Compounds: Compare ways in which atoms combine to form molecules and compounds.

• Organic vs. Inorganic Compounds: Distinguish between organic and inorganic compounds.

• Chemical Properties of Water: Explain how chemical properties of water make life possible.

• ATP Function: Discuss the structure and function of adenosine triphosphate (ATP).

Atoms and Atomic Structure

Definition and Properties

• Atom: The smallest unit of matter that retains its original properties.

• Nucleus: Central core of atom containing protons and neutrons.

• Protons: Positively charged subatomic particles.

• Neutrons: Subatomic particles with no charge.

• Electrons: Negatively charged subatomic particles that orbit the nucleus.

• Electrical Neutrality: Atoms have equal numbers of protons and electrons, resulting in no overall charge.

• Chemical Reactions: Can cause atoms to become charged (ions).

Elements

• Element: Substance composed of one or more identical atoms; cannot be broken down by chemical means.

• Atomic Number: Defined by the number of protons in the nucleus.

Periodic Table of Elements

The periodic table organizes elements by atomic number and properties. The first three rows include:

Major and Trace Elements in the Human Body

• Major Elements: Oxygen (O), Carbon (C), Hydrogen (H), Nitrogen (N)

• 7 Mineral Elements: Calcium (Ca), Phosphorus (P), Magnesium (Mg), Potassium (K), Sodium (Na), Chloride (Cl), Sulfur (S)

• 13 Trace Elements: Chromium (Cr), Cobalt (Co), Copper (Cu), Fluorine (F), Iron (Fe), Manganese (Mn), Molybdenum (Mo), Nickel (Ni), Selenium (Se), Silicon (Si), Vanadium (V), Zinc (Zn)

Electron Shells

• Electron Shells: Regions surrounding the nucleus containing electrons.

• 1st Shell: Holds up to 2 electrons (closest to nucleus).

• 2nd Shell: Holds up to 8 electrons.

• 3rd Shell: Holds up to 18 electrons, but is stable with 8.

• Valence Shell: Outermost shell; electrons here are called valence electrons.

• Some atoms may have more than 3 shells.

Stability and Chemical Bonds

Stability of Atoms

• Duet Rule: Atoms with 2 or fewer electrons are stable when their outer shell has 2 electrons (e.g., Hydrogen).

• Octet Rule: Atoms are most stable with 8 electrons in the valence shell.

• Unstable atoms are more likely to form chemical bonds.

Chemical Bonds

• Molecule: Forms when 2 or more atoms of the same element are chemically bonded.

• Compound: Forms when 2 or more atoms of different elements are chemically bonded.

Ionic Bonds

• Ionic Bond: Electrons are transferred between a metal atom and a nonmetal atom.

• Ion: Charged particle.

• Cation: Positively charged ion.

• Anion: Negatively charged ion.

• Oppositely charged ions attract to form electrolytes (salts).

Covalent Bonds

• Covalent Bond: Electrons are shared between two or more nonmetal atoms; strongest type of chemical bond.

• Single bond: 1 electron pair shared.

• Double bond: 2 electron pairs shared.

• Triple bond: 3 electron pairs shared.

• Nonpolar Covalent Bond: Electrons are shared equally (e.g., O2, N2, CO2, H2).

• Polar Covalent Bond: Electrons are shared unequally, creating partial positive and negative poles.

Hydrogen Bonds

• Hydrogen Bond: Weak attractions between partially positive and partially negative atoms in polar covalent molecules (not true bonds).

Relative Bond Strength

• Weakest: Hydrogen Bonds

• Polar Covalent Bonds

• Covalent Bonds: Single < Double < Triple

• Ionic Bonds: Relatively strong but variable

Physiologically Important Properties of Water

Water in the Human Body

• Water makes up 50–65% of the mass of the human body.

Surface Tension

• Water molecules cluster together and form hydrogen bonds, creating a 'web' of molecular connections.

• Surface tension is the reason water forms droplets.

Solubility

• Solution: Solvent with dissolved solutes.

• Solvent: Liquid that dissolves solutes (water is the body's solvent).

• Solute: Dissolved molecules (e.g., sugar, salt).

• Hydrophobic Solutes: Cannot dissolve nonpolar molecules.

High Heat Capacity

• Water absorbs heat without significant temperature change.

Thermoregulation

• Water carries heat with it when changing from liquid to gas (e.g., sweating cools the body).

Protection & Lubrication

• Water cushions and protects body structures.

• Acts as a lubricant between adjacent surfaces (e.g., joints).

Organic vs. Inorganic Molecules

Definitions and Comparison

Adenosine Triphosphate (ATP)

Structure and Function

• ATP: Adenosine triphosphate is the primary energy carrier in cells.

• Energy is released when ATP is hydrolyzed to ADP (adenosine diphosphate) and inorganic phosphate.

Equation for ATP hydrolysis:

• ATP powers cellular processes such as muscle contraction, nerve impulse transmission, and biosynthesis.

Additional Info

• Periodic Table: The "red staircase" on the periodic table separates metals (left) from nonmetals (right).

• Free Radicals: Unstable, reactive molecules with unpaired electrons; can damage cells and DNA.

• Antioxidants: Prevent cellular damage by donating electrons to free radicals; found in fruits and vegetables.