Chemistry and Physics Fundamentals: Units, Atoms, Equations

Posted on Jul 9, 2025 in Documentation, Library, and Archive Management

Key Topics in Chemistry and Physics Fundamentals

Chapter 1: Physical Quantities and Measurement Systems

Defining Physical Quantities

A physical quantity is a measure of fundamental properties such as mass, length, time, and temperature.

Common Measurement Systems

  • MKS System: Mass (kilograms, kg), Length (meters, m), Time (seconds, s), Temperature (Kelvin, K)
  • CGS System: Mass (grams, g), Length (centimeters, cm), Time (seconds, s), Temperature (Kelvin, K)

Metric Prefixes and Powers of Ten

PrefixSymbolValuePower of 10
petaP1,000,000,000,000,0001015
teraT1,000,000,000,0001012
gigaG1,000,000,000109
megaM1,000,000106
kilok1,000103
hectoh100102
decada10101
1100
decid0.110-1
centic0.0110-2
millim0.00110-3
microµ0.00000110-6
nanon0.00000000110-9
picop0.00000000000110-12
femtof0.00000000000000110-15

Extensive vs. Intensive Properties

  • Extensive Properties: Depend on the amount of matter present (e.g., Energy, Mass).
  • Intensive Properties: Do not depend on the amount of matter present (e.g., Density, Pressure, Temperature).

Note: Pressure is not equivalent to energy per unit volume.

Chapter 2: Atomic Structure and Composition

Atomic Composition

Atoms are composed of subatomic particles: protons, neutrons, and electrons, which carry electrical charges.

  • Electrical forces within neutral atoms typically balance out.
  • Typical nucleus size: 10-13 cm

Subatomic Particle Masses

  • Electron Mass: 9.1 x 10-28 g or 9.1 x 10-31 kg
  • Proton Mass: 1.67 x 10-24 g or 1.7 x 10-27 kg
  • Neutron Mass: 1.67 x 10-24 g or 1.7 x 10-27 kg (slightly heavier than a proton)

Key Atomic Concepts

  • Atomic Number (Z): The number of protons in an atom’s nucleus, defining the element.
  • To count atoms in a chemical formula, identify each element and its subscript.
  • Atomic Mass Units (AMUs): Used to express atomic and molecular masses.
  • Isotopes: Different versions of the same atom, having the same number of protons but different numbers of neutrons.
  • Average Atomic Mass: The weighted average of the masses of an element’s isotopes. Calculated as: (percent abundance of isotope 1 × mass of isotope 1) + (percent abundance of isotope 2 × mass of isotope 2) + …
  • Avogadro’s Number (NA): 1 mole (mol) = 6.022 × 1023 particles (atoms, molecules, ions, etc.).

Key Conversions and Fundamental Units

Fundamental Units of Measurement

  • The basic unit of length is the meter (m).
  • The basic unit of volume is the liter (L).
  • The basic unit of mass is the gram (g).

Temperature Conversions

  • °F = 9/5(°C) + 32
  • °C = 5/9(°F – 32)
  • K = °C + 273

Pressure Conversions

  • 1 atm = 760 mmHg = 760 torr

Length Conversions

  • 1 inch (in) = 2.54 centimeters (cm)
  • 1 foot (ft) = 12 inches (in)
  • 1 yard (yd) = 36 inches (in)
  • 1 mile = 5280 feet (ft)

Mass Conversions

  • 1 pound (lb) = 454 grams (g)
  • 1 pound (lb) = 16 ounces (oz)
  • 1 metric ton = 1000 kg
  • 1 ton (US) = 2000 pounds (lb)

Volume Conversions

  • 1 quart (qt) = 0.946 liters (L)
  • 1 milliliter (mL) = 1 cubic centimeter (cc or cm3)
  • For water only: 1 milliliter (mL) = 1 cubic centimeter (cm3) = 1 gram (g)
  • 1 gallon (gal) = 4 quarts (qt)
  • 1 quart (qt) = 2 pints (pt)
  • 8 fluid ounces (fl oz) = 1 cup
  • 16 fluid ounces (fl oz) = 1 pint (pt)
  • 32 fluid ounces (fl oz) = 1 quart (qt)

How to Balance a Chemical Equation

When balancing chemical equations, you should only change the coefficients in front of the chemical symbols. Never change the subscripts within the chemical compounds. The following steps outline the balancing process:

  1. Count Atoms: Add up the number of each kind of atom on both the reactants side and the products side of the chemical equation.

  2. Apply Coefficients: Use coefficients in front of each compound to balance the number of each kind of atom or polyatomic ion, one at a time. This may require trial and error, moving back and forth between the reactants and products. For simplicity, start by balancing the atoms or polyatomic ions that appear in the fewest compounds.

  3. Verify Balance: Check the equation to ensure that each kind of atom or polyatomic ion is balanced on both sides.

  4. Simplify Coefficients: Put the balanced equation into its lowest terms. If all coefficients can be evenly divided by the same positive integer, then do so.