Chemistry Chapter on Atomic Structure and Properties

Atomic Structure

• Electrons orbit the nucleus in a spherical electron cloud, constituting the electron shell.
• Element's mass number = number of protons + number of neutrons in the nucleus.
• Neutrons carry no charge but contribute significant mass.
• Isotopes are variants of the same element differing in mass due to neutron count; radioisotopes emit radiation and decay at a specific half-life.

Chemical Properties and Atoms

• Atomic weight is crucial for chemical reactions; chemists measure chemicals using atomic weight.
• A mole (mol) is the quantity of an element whose weight in grams equals its atomic weight.
• Atoms can be neutral (equal protons and electrons) or ionic (unequal protons/electrons).
• Energy levels denote specific electron capacity: Level 1 holds 2 electrons; Levels 2 and 3 hold 8 electrons each.

Water and pH Regulation

• Water has a neutral pH of 7.0, with equal concentrations of H+ and OH- ions.
• pH scale ranges:
  • pH < 7 indicates acidity (high H+, low OH-);
  • pH > 7 indicates basicity (low H+, high OH-).
• pH influences physiological functions; excessive H+ can damage cells and proteins, while excess OH- is rare.

Acids, Bases, and Salts

• Acids release H+ ions, lowering pH; thus, they're termed proton donors.
• Excess acidity leads to acidosis; bases accept H+ ions, raising pH (proton acceptors).
• Salts consist of cations and anions but do not release H+ or OH- ions, typically not affecting solution pH.

Buffers

• Buffers consist of weak acids and bases, stabilizing pH by reacting with H+ ions in a reversible manner, neutralizing strong acids or bases.

Organic Compounds

• Organic compounds are large molecules primarily made of carbon, hydrogen, and oxygen.
• Four major classes: carbohydrates, lipids, proteins, nucleic acids.
• Functional groups (e.g., carboxyl, amino, hydroxyl, phosphate) allow interaction with other molecules.

Carbohydrates

• Composed of a carbon/hydrogen/oxygen ratio of ~1:2:1.
• Categories include:
  • Monosaccharides: simple sugars (e.g., glucose, fructose).
  • Disaccharides: two simple sugars (e.g., sucrose) formed via dehydration synthesis and broken down by hydrolysis.
  • Polysaccharides: large chains (e.g., cellulose, starch, glycogen) utilized for energy storage and structure.

Lipids

• Lipids are hydrophobic molecules (e.g., fats, oils), primarily composed of carbon and hydrogen.
• Five main classes include fatty acids, eicosanoids, glycerides, steroids, and phospholipids.
  • Fatty acids can be saturated, monounsaturated, or polyunsaturated.
  • Eicosanoids: signaling molecules derived from arachidonic acid.
  • Glycerides consist of varying numbers of fatty acids for energy, insulation, and protection.
  • Steroids have a four-ring structure; key examples include cholesterol and sex hormones.
  • Phospholipids form cell membranes due to hydrophilic heads and hydrophobic tails.

Proteins

• Composed mainly of carbon, hydrogen, oxygen, and nitrogen; essential for all body functions.
• Seven major functions include support, movement, transport, buffering, metabolic regulation, coordination, and defense.
• Building blocks: amino acids (with central carbon, hydrogen, amino group, carboxylic acid group, and variable side chain).
• Peptide bonds form between amino acids to create polypeptides; proteins require specific folding to function.
• Protein structure levels: primary (amino acid sequence), secondary (hydrogen bonds), tertiary (3D folding), quaternary (multiple chains).

Nucleic Acids

• Large organic molecules made of carbon, hydrogen, oxygen, nitrogen, and phosphorus, responsible for storage and processing molecular information.