Chap 2 Elements, Atoms, Molecules, and Compounds

• An element is a pure substance consisting of one type of atom.
• An atom is the smallest unit of matter that retains the chemical properties of an element.
• A molecule is two or more atoms held together by chemical bonds.
• A compound is a substance composed of two or more different elements chemically bonded.
• The six elements that make up 98.5% of body weight are oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus.
• Atoms consist of protons, neutrons, and electrons.
• Protons have a positive charge and are located in the nucleus.
• Neutrons have no charge and are located in the nucleus.
• Electrons have a negative charge and orbit the nucleus in electron shells.
• The number of electrons in a neutral atom equals the number of protons.
• Number of neutrons is the atomic mass minus the number of protons
• The atomic number is the number of protons in an atom.
• The mass number is the total number of protons and neutrons in an atom's nucleus.
• Isotopes are atoms of the same element with different numbers of neutrons.
• Radioactive isotopes are unstable isotopes that emit radiation as they decay.
• Radioactive isotopes are used in medicine for:
  • Tracers in diagnostic imaging
  • Radiation therapy to treat cancer
• Cations are positively charged ions formed when an atom loses electrons.
• Anions are negatively charged ions formed when an atom gains electrons.
• Chemical bonds in order of relative strength: covalent bonds, ionic bonds, hydrogen bonds, van der Waals interactions.
• The octet rule states that atoms tend to gain, lose, or share electrons in order to achieve a full outer electron shell with eight electrons, providing stability.
• Ionic bonds result from the transfer of electrons between atoms, creating ions that are attracted to each other.
• Nonpolar covalent bonds involve equal sharing of electrons between atoms.
• Polar covalent bonds involve unequal sharing of electrons between atoms, creating partial charges.
• Hydrogen bonds are weak bonds between a hydrogen atom in one molecule and a highly electronegative atom (like oxygen or nitrogen) in another molecule.
• DNA is linked by hydrogen bonds
• A mixture is a combination of substances that are physically mixed but not chemically bonded.
• A solution is a homogeneous mixture where a solute is dissolved in a solvent.
• A solute is the substance being dissolved.
• A solvent is the substance doing the dissolving.
• A colloid is a mixture with particles larger than those in a solution but small enough to remain dispersed.
• A suspension is a mixture with large particles that will settle out over time An example is blood
• Five biologically important properties of water:
  • Cohesion
  • Adhesion
  • High heat capacity
  • Excellent solvent
  • Essential reactant
• Hydrophilic molecules mix easily with water.
• Hydrophobic molecules do not mix easily with water.
• Hydrolysis is the breakdown of a molecule by the addition of water.
• Dehydration synthesis is the formation of a molecule by removing water.
• pH is a measure of the acidity or alkalinity of a solution.
• An acid is a substance that donates hydrogen ions (H+) to a solution.
• A base is a substance that accepts hydrogen ions or releases hydroxide ions (OH-) into a solution.
• A buffer is a substance that resists changes in pH by accepting or donating hydrogen ions.
• Energy is the capacity to do work.
• Work is the movement of an object or a change in its physical properties.
• Potential energy is stored energy.
• Kinetic energy is the energy of motion.
• Decomposition reactions break down molecules into smaller components (e.g., hydrolysis).
• Synthesis reactions combine molecules to form larger molecules (e.g., dehydration synthesis).
• Factors that increase reaction rates:
  • Higher temperature
  • Higher concentration of reactants
  • Presence of a catalyst
• Metabolism is the sum of all chemical reactions in the body.
• Anabolism is the synthesis of complex molecules from simpler ones.
• Catabolism is the breakdown of complex molecules into simpler ones
• An organic molecule is one that contains carbon.
• Macromolecules are large polymers.
• Polymers are molecules made of repeating monomer subunits.
• Monomers are the building blocks of polymers.
• Carbohydrates are composed of monosaccharides (monomers) linked together.
• Lipids are related through their hydrophobic nature and include triglycerides, phospholipids, and steroids; functions vary from energy storage to cell membrane structure.
• Triglycerides consist of a glycerol molecule and three fatty acids; phospholipids have a phosphate group and two fatty acids.
• Triglycerides are transported in the human body via lipoproteins.
• The "parent" steroid from which other steroids are synthesized is cholesterol.
• Amino acids are the monomers of proteins, linked by peptide bonds.
• Protein structure has four levels:
  • Primary (amino acid sequence)
  • Secondary (local folding patterns like alpha-helices and beta-sheets)
  • Tertiary (3D structure of a single protein)
  • Quaternary (arrangement of multiple protein subunits).
• Fibrous proteins are elongated and structural
• Globular proteins are compacted and functional
• Proteins can denature (lose their structure) due to:
  • Heat
  • pH changes
• Enzymes are biological catalysts that speed up chemical reactions by lowering activation energy.
• The three nucleic acids in the human body are:
  • DNA
  • RNA
  • ATP
• Nucleotides are composed of a sugar, a phosphate group, and a nitrogenous base.

This lesson covers the basics of elements, atoms, molecules, and compounds. It also discusses the structure of atoms, including protons, neutrons, and electrons. Key concepts like atomic number, mass number, and isotopes are explained.