Chapter 2 The Chemical Basis of Life Lecture Outline

Matter and Elements

• Matter: Anything that takes up space and has mass; can be solid, liquid, or gas.

• Elements: Substances that can't be broken down by ordinary chemical means.

  • Examples: carbon, hydrogen, nitrogen, oxygen, sulfur, and phosphorus.

• Atoms are the smallest unit of matter retaining an element's chemical properties.

Atomic Structure

• Atoms consist of a nucleus (protons and neutrons) and orbiting electrons.

• Subatomic Particles:

  • Neutrons: Neutral charge, mass of 1 amu.

  • Protons: +1 charge, mass of 1 amu.

  • Electrons: -1 charge, negligible mass.

• Atomic Number: Number of protons, identifies the element.

• Mass Number: Sum of protons and neutrons.

• Atomic Mass: Average mass of all isotopes of an atom.

• Isotopes: Atoms of the same element with different neutron numbers.

• Radioactive Isotopes: Unstable nuclei that emit radiation, used in PET scans and sterilization.

Organization of Elements

• Atomic Symbol: Abbreviation for an element.

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

• Periods (rows): Indicate number of electron shells.

• Groups (columns): Indicate number of valence electrons.

Electron Arrangement

• Electrons occupy shells or energy levels around the nucleus.

• Octet Rule: Atoms are most stable with eight valence electrons (except for the innermost shell, which needs two).

Chemical Properties and Reactions

• Determined by valence electron arrangement.

• Ions: Atoms that gain or lose electrons.

  • Cations: Positive ions (lose electrons).

  • Anions: Negative ions (gain electrons), named with "-ide" suffix.

• Molecular Formula: Indicates number of atoms in a molecule (e.g., C6H{12}O_6).

• Chemical Reactions: Atoms bonding to form molecules or breaking apart.

  • Reactants: Starting substances.

  • Products: Ending substances.

• Balanced Equations: Same number of atoms for each element on both sides.

• Molecules: Two or more atoms chemically bonded (O2, H2O).

• Compounds: Molecules with two or more different elements (H2O, C6H{12}O6).

• Reversible Reactions: Can proceed in both directions, reaching equilibrium (HCO3^- + H^+ \leftrightarrow H2CO_3).

Chemical Bonds

• Ionic Bonds: Transfer of electrons between ions with opposite charges (e.g., NaCl).

• Covalent Bonds: Sharing electrons.

  • Nonpolar Covalent Bonds: Equal sharing (e.g., O2, CH4).

  • Polar Covalent Bonds: Unequal sharing, creating partial charges (e.g., H_2O).

• Hydrogen Bonds: Attraction between opposite partial charges (critical for water properties, protein and DNA structure).

• Van der Waals Interactions: Weak attractions between molecules due to electron density fluctuations; important for protein structure.