Learn & Review: Atoms, Chemical Bonds, Water, pH: Chemistry - Microbiology for Pre-Med/Nursing

Review of Important Chemistry Concepts for Understanding Microorganisms

This video reviews essential chemistry concepts relevant to understanding the structure and function of microorganisms, including atoms, ions, chemical bonds, pH, and water.

Components of an Atom

• Proton:
  • Positively charged particle.
  • Located in the nucleus.
  • Mass: 1 atomic mass unit (amu).
  • Charge: +1.
  • The number of protons defines the element.
• Electron:
  • Negatively charged particle.
  • Found in energy shells around the nucleus.
  • Mass: Negligible.
  • Charge: -1.
  • Valence electrons (electrons in the outermost shell) determine an atom's chemical properties and reactivity.
    • Atoms with an incomplete outer shell (e.g., 7 electrons) are reactive and tend to form bonds.
    • Atoms with a full outer shell (e.g., 8 electrons) are stable and unreactive.
• Neutron:
  • Neutrally charged particle.
  • Located in the nucleus.
  • Mass: 1 amu.
  • Charge: 0.

Electronegativity

• Definition: The measure of an atom's ability to attract electrons towards itself.
• Trends on the Periodic Table:
  • Decreases as you go down a group.
  • Increases as you go from left to right across a period.
• Significance: Helps understand ion formation and the nature of covalent bonds (polar vs. nonpolar). Fluorine is the most electronegative element.

Atoms and Ions

• Uncharged Atom: Has an equal number of protons and electrons, resulting in no net charge.
• Ion: Has an unequal number of protons and electrons, resulting in a net positive or negative charge.
  • Cation:
    • A positive ion.
    • Forms when an atom loses an electron(s).
    • Number of electrons < Number of protons.
    • Mnemonic: "I positively love cats."
  • Anion:
    • A negative ion.
    • Forms when an atom gains an electron(s).
    • Number of electrons > Number of protons.
    • Mnemonic: Anakin Skywalker was negative.

Chemical Bonds

• Covalent Bond:
  • Formed by the sharing of electrons between two atoms.
  • Strongest and most common type in living organisms.
  • Nonpolar Covalent Bond: Electrons are shared equally due to no difference in electronegativity between atoms.
    • Example: Bond between hydrogen and carbon.
  • Polar Covalent Bond: Electrons are shared unequally; pulled closer to the more electronegative atom.
    • Example: Bond between oxygen and hydrogen (oxygen is more electronegative, gaining a slight negative charge; hydrogen gains a slight positive charge).
• Ionic Bond:
  • Results from the electrostatic attraction between a cation (positive ion) and an anion (negative ion).
  • Example: Sodium chloride (NaCl).
• Hydrogen Bond:
  • A weak attractive force between a weakly positive hydrogen atom on one molecule and a weakly negative oxygen, nitrogen, or fluorine atom on another molecule.
  • No electrons are lost, gained, or shared.
  • Example: Bonds between two water molecules.

Water and Related Terms

• Solvent: A substance capable of dissolving another substance. Water is an excellent solvent due to its polarity.
• Solute: The substance that is being dissolved.
• Hydrophilic:
  • "Water-loving."
  • Molecules that can form hydrogen bonds with water and dissolve in it.
  • Example: Polar sugar molecules.
  • Mnemonic: "I'm in love with Phil."
• Hydrophobic:
  • "Water-fearing."
  • Nonpolar substances that do not form hydrogen bonds with water and do not dissolve in it.
  • Example: Oils and fats.

pH

• Definition: A measure of the hydrogen ion (H+) concentration of a solution. Calculated as the negative logarithm of the H+ concentration.
• pH Scale: Ranges from 0 to 14.
  • A change of one pH unit represents a tenfold change in H+ concentration.
• Neutral: pH of 7. Equal concentration of hydrogen ions (H+) and hydroxide ions (OH-).
• Acid:
  • pH less than 7.
  • Donates hydrogen ions (H+) to the solution.
  • H+ concentration > OH- concentration.
  • Examples: Stomach acid, lemon juice.
• Base (Alkaline):
  • pH greater than 7.
  • Removes hydrogen ions (H+) from the solution.
  • H+ concentration < OH- concentration.
  • Examples: Ammonia, bleach.

Quiz Review

1. A cation is a positive ion that forms when an atom loses an electron to a more electronegative atom.
2. A nonpolar covalent bond is formed when electrons are shared equally between atoms.
3. A hydrogen bond is a weak attractive force between a hydrogen atom on one molecule and an oxygen atom on another molecule.
4. A water-loving molecule that can be dissolved in water is described as hydrophilic.
5. A substance that donates hydrogen ions into a solution, resulting in a pH less than seven, is considered an acid.