1: Chemistry & Physics

Atomic Bonding

Definition of an Ion

  • An ion is an atom that carries a positive or negative charge.

Types of Bonds

Ionic Bonds
  • An ionic bond involves the complete transfer of valence electron(s) from one atom to another.
    • This process leaves one atom with a negative charge (anion) and the other with a positive charge (cation).
    • Metals tend to form ionic bonds. They’re also common with acids and bases.
Covalent Bonds
  • A covalent bond involves the equal sharing of electrons between atoms.
    • Single Bond: Created when one pair of electrons is shared.
    • Double Bond: Created when two pairs of electrons are shared.
    • Triple Bond: Created when three pairs of electrons are shared.
Polar Covalent Bonds
  • Atoms share electrons, but the electrons tend to remain closer to one atom than the other.
    • Example: Water, where the region near the oxygen atom is relatively negative and regions near each hydrogen atom are relatively positive.
Van der Waals' Forces
  • Van der Waals' forces describe a very weak intermolecular force that holds molecules of the same type together.

Molecular Bonds in Decreasing Order of Strength

  • Covalent > Ionic > Polar Covalent

Matching Definition to Bond Types

  • Polar Covalent: Unequal sharing of valence electrons.
  • Covalent: Equal sharing of valence electrons.
  • Ionic: Complete transfer of valence electrons.

Atoms

Components of an Atom

An atom is the basic building block that makes up all matter, consisting of:

  1. Protons (+ charge)
  2. Neutrons (no charge)
  3. Electrons (- charge)

Structure of an Atom

  • The protons and neutrons reside at the center of the atom, forming the nucleus.
  • The number of protons in the nucleus determines the atom's atomic number.
  • The electrons orbit the nucleus in the electron cloud, attracted to the nucleus due to their negative charge.

Electron Shells

  • Electrons travel in predictable orbital patterns called shells.
    • Each shell has a predefined number of electrons, which must be complete before filling the next shell.
    • The electrons in the outermost shell are called valence electrons.
    • An incomplete shell allows an atom to react with another atom, while a full shell makes the atom non-reactive (inert).

Molecules

  • Two or more atoms bonded together are called a molecule.

Electrical Charge and Ions

Charge of an Atom

  • An atom will have a:
    • Neutral charge if: ext{# electrons} = ext{# protons}
    • Positive charge if: ext{# electrons} < ext{# protons}
    • Negative charge if: ext{# electrons} > ext{# protons}

Definition of Ions

  • An ion is an atom that carries a positive or negative charge.
    • An atom with a positive charge (it has lost electrons) is called a cation.
    • An atom with a negative charge (it has gained electrons) is called an anion.
  • Metals tend to ionize, while non-metals do not.

Chemical Bonding

Ionic Bond

  • Involves the complete transfer of valence electron(s) from one atom to another, leaving one atom with a negative charge and the other with a positive charge.
  • Metals tend to form ionic bonds and they are common with acids and bases.

Covalent Bond

  • Involves the equal sharing of electrons:
    • Single Bond: One pair of electrons shared.
    • Double Bond: Two pairs of electrons shared.
    • Triple Bond: Three pairs of electrons shared.

Polar Covalent Bond

  • An “in-between” type of bond where atoms share electrons, but the electrons tend to remain closer to one atom.
    • Creates a polar molecule with a relatively positive and negative area.
    • Example: Water.
Implications
  • The polar nature allows different properties such as hydrogen bonding in water.
  • Water as a polar molecule is attracted to other polar molecules and ions which explains why hydrophilic solutes dissolve in water, while non-polar substances do not.

Van der Waals Forces

  • Describe weak intermolecular forces that hold molecules of the same type together.
  • These forces arise from temporary partial charges induced by the motion of electrons around the nuclei of the atoms involved.

Dalton's Law

Definition

  • Dalton's law relates to gas pressures, stating that the total pressure is equal to the sum of the partial pressures exerted by each gas in the mixture:
    • P<em>total=P</em>1+P<em>2+P</em>3+…+PnP<em>{total} = P</em>1 + P<em>2 + P</em>3 + … + P_n

Applications

  • Calculate the pressure of an unmeasured gas.
  • Calculate total pressure in a gas mixture.
  • Convert partial pressure to volume percent, and vice versa.

Practice Questions

  1. Calculate P3:
    • Total Pressure = 100 mmHg
    • P1=20mmHgP_1 = 20 mmHg
    • P2=20mmHgP_2 = 20 mmHg
    • P3=XmmHgP_3 = X mmHg
  2. Calculate the total pressure of a gas mixture:
    • P1=30mmHgP_1 = 30 mmHg
    • P2=40mmHgP_2 = 40 mmHg
    • P3=50mmHgP_3 = 50 mmHg
    • Total = X mmHg

Answers to Practice Questions

  1. X=60extmmHgX = 60 ext{ mmHg}
  2. X=120extmmHgX = 120 ext{ mmHg}

Henry's Law

Definition

  • At a constant temperature, the amount of gas that dissolves in a solution is directly proportional to the partial pressure of that gas over the solution.

Applications

  • Prolonged anesthetic emergence in hypothermic patients.
  • Overpressuring the vaporizer.
  • Increasing FiO2 increases PaO2.
Solubility Coefficients
  • Each gas has a unique solubility coefficient representing how easily it can be put into a solution:
    • Oxygen: 0.003 mL/dL/mmHg
    • Carbon dioxide: 0.067 mL/dL/mmHg
  • $CO2$ is ~20 times more soluble than $O2$.

Fick's Law of Diffusion

Definition

  • Fick's law describes the transfer rate of a gas through a tissue medium:
    • Rate of Transfer Proportional To:
    • Partial pressure difference (driving force)
    • Diffusion coefficient (solubility)
    • Membrane surface area
    • Rate of Transfer Inversely Proportional To:
    • Membrane thickness
    • Molecular weight

Applications

  • Cardiac output calculation.
  • Placental drug transfer.

Graham's Law

Definition

  • States that the molecular weight of a gas determines how fast it can diffuse through a membrane:
    • Rate of diffusion (or effusion) is inversely proportional to the square root of the gas's molecular weight.
  • Smaller molecules diffusing faster than larger ones.

Applications

  • Second gas effect (using $N_2O$ to hasten the onset of a volatile anesthetic).
  • High fresh gas flow is turbulent as it passes through the annular space.

Gas Laws

Boyle's Law

  • States the volume and pressure of a gas are inversely proportional at constant temperature:
    • P<em>1imesV</em>1=P<em>2imesV</em>2P<em>1 imes V</em>1 = P<em>2 imes V</em>2

Charles' Law

  • At constant pressure, the temperature and volume of a gas are directly proportional:
    • rac{V1}{T1} = rac{V2}{T2}

Gay-Lussac's Law

  • At a constant volume, the temperature and pressure of a gas are directly proportional:
    • rac{P1}{T1} = rac{P2}{T2}

Ideal Gas Law

  • Unifies the three gas laws into one equation:
  • PV=nRTPV = nRT
  • $P$ = pressure, $V$ = volume, $n$ = number of moles, $R$ = constant (0.0821 L-atm/K-mole), $T$ = temperature.

Ohm's Law & Poiseuille's Law

Ohm's Law

  • States that the current passing through a conductor is directly proportional to the voltage and inversely proportional to the resistance:
    • ext{Current} = rac{ ext{Voltage}}{ ext{Resistance}}

Poiseuille's Law

  • Adaptation of Ohm's law for fluid flow; flow is directly proportional to pressure gradient and inversely proportional to resistance.
    • Q = rac{ ext{AP} imes ext{R}^4}{8 ext{nL}}
    • Applications: Increasing the radius increases flow significantly.
    • Example: Doubling the radius increases flow by a factor of 16.

Flow Characteristics

Types of Flow
  1. Laminar Flow:
    • Re < 2000
    • Molecules travel in parallel patterns.
  2. Turbulent Flow:
    • Re > 4000
    • Molecules travel in chaotic patterns (producing eddies).
  3. Transitional Flow:
    • Re=2000−4000Re = 2000 - 4000
    • Chaotic in center and laminar near walls.
Reynolds' Number
  • Useful for predicting flow types based on
  • Resistance of laminar flow depends on viscosity, turbulent flow depends on density.

Examples of Gas Laws in Practice

Boyle's Law
  • Useful for understanding changes in volume during diaphragm contraction; used in pneumatic ventilation.
Charles' Law
  • Important for understanding changes in gas volume with temperature; e.g., LMA cuff failures.
Gay-Lussac's Law
  • Important for understanding pressure changes during heating; e.g., oxygen tank explosions.

Summary of Gas Laws

  • Boyle's, Charles', and Gay-Lussac's laws each affect how gases behave under varying conditions and can be summarized by a mnemonic: "Paid TV Can Be Great".

Radiation Safety

Ionizing Radiation

  • Can remove electrons from atoms and create free radicals, leading to cellular damage, chromosomal injury, and malignancies.
  • Exposure follows the inverse square law: Exposure is inversely proportional to the square of the distance from the source.

Safe Exposure Guidelines

  • The minimum safe distance in OR is 6 feet.
  • Maximum yearly exposure for adults is 5 rem, for fetuses it is 0.5 rem (or 0.05 rem/month).

Protection Methods

  1. Distance
  2. Duration
  3. Shielding (e.g., lead aprons)

Miscellaneous Concepts

Key Definitions

  1. Evaporation: Transition from liquid to gas at a temp below boiling point.
  2. Boiling: Occurs when vapor pressure equals atmospheric pressure.
  3. Specific Heat: Amount of heat to increase 1 gram of a substance by 1°C.
  4. Latent Heat of Vaporization: Calories to convert 1 gram of liquid to vapor without a temp change.
  5. Critical Temperature: Highest temp for gas to exist as liquid.
  6. Critical Pressure: Minimum pressure to liquefy a gas at its critical temperature.
Units of Measurement
  • Common pressure conversions include:
    • 1 atm = 760 mmHg = 760 torr = 1 bar = 100 kPa = 1033 cm H2O = 14.7 lb/in².