Essentials of Biology - Chemical Basis of Life Summary

The Chemical Basis of Life

Elements and Matter

  • Matter:
    • Anything that takes up space and has mass.
    • Exists as solid, liquid, or gas.
    • Composed of elements.
  • Element:
    • Cannot be broken down into another substance by ordinary chemical means.
    • Differ in chemical and physical properties.
    • Abundant elements in organisms: carbon, hydrogen, nitrogen, oxygen, sulfur, and phosphorus.

Atomic Structure

  • Atomic Theory: Elements consist of atoms.
  • Atom: Smallest unit of matter retaining element's chemical properties.
  • Atoms consist of:
    • Nucleus: Contains protons and neutrons.
    • Electrons: Orbit around the nucleus.
  • Subatomic Particles:
    • Neutrons: 0 charge, mass 1 amu.
    • Protons: +1 charge, mass 1 amu.
    • Electrons: -1 charge, mass ~0 amu.
  • Mass number: Sum of protons and neutrons.
  • Atomic number: Number of protons, distinguishes elements.
  • Atomic mass: Average mass number for all isotopes of an atom.
  • Atomic symbol: Abbreviation for the element.

Periodic Table

  • Displays elements by chemical and physical characteristics.
  • Elements organized by atomic number in rows and columns.
  • Rows (periods): Indicate number of energy shells.
  • Columns (groups): Indicate number of electrons in outermost shell.

Isotopes

  • Atoms of the same element with different numbers of neutrons.
  • Radioactive isotopes: Unstable nuclei that emit radiation.
  • PET Scan:
    • Uses radioactive tracers.
    • Detects tumors, Alzheimer's, epilepsy, stroke.

Electron Arrangement and Chemical Properties

  • Electrons occupy electron shells or energy levels.
  • Octet Rule: Atoms are more stable with eight electrons in the valence shell (outermost shell).
  • Valence shell: Outermost electron shell.
  • Chemical properties depend on electron arrangement in the valence shell.

Chemical Reactions and Equations

  • Reactants: Substances at the beginning of a chemical reaction.
  • Products: Substances at the end of a chemical reaction.
  • Law of Conservation of Matter: Atoms are neither created nor destroyed.
  • Balanced Equation: Equal number of atoms for each element on both sides.
  • Molecule: Two or more atoms chemically bonded.
  • Compound: Molecule made of atoms from 2 or more different elements.
  • Reversible Reactions: Can proceed in both directions, leading to equilibrium.

Chemical Bonds

  • Chemical Bond: Forces holding atoms together.
  • Types of Bonds:
    • Ionic Bonds: Transfer of electrons, attraction between opposite charges.
    • Covalent Bonds: Sharing electrons to complete outer shell.
      • Polar Covalent Bonds: Unequal sharing of electrons, partial charges (δ+ or δ–).
      • Nonpolar Covalent Bonds: Equal sharing of electrons.
    • Hydrogen Bonds: Attraction of opposite partial electrical charges.
    • Van der Waals Interactions: Weak attractions between molecules due to temporary fluctuations in electron density.

Ionic Bonds and Electrolytes

  • Electron Transfer: Movement of electrons from one element to another.
  • Ions: Charged atoms.
    • Cations: Positive ions formed by losing electrons.
    • Anions: Negative ions formed by gaining electrons.
  • Salts: Solid substances formed by ionic bonds.
  • Electrolytes: Ions (e.g., sodium, potassium, calcium) necessary for nerve impulse conduction, muscle contractions, and water balance.