CHEM1113 Essential Concepts - module 1 08/26/25

Scientific Method and Core Ideas

  • Science is empirical: knowledge comes from observation and experiment.

  • Hypothesis: tentative explanation; must be falsifiable.

  • Scientific Law: concise statement that summarizes past observations and predicts future ones; cannot be violated by experiments.

  • Theory: well-established set of ideas explaining why a phenomenon occurs; validated by experiments but never proven beyond doubt.

  • Matter is composed of particles; chemistry seeks to understand matter and its properties.

Building Blocks and History of Matter

  • Early ideas: Leucippus and Democritus proposed indivisible particles (atoms).

  • Classical view: Plato/Aristotle argued matter has no smallest parts and can be divided into proportions of fire, air, earth, water.

Matter from Particulate Perspective

  • Matter consists of particles; properties arise from how particles are arranged.

  • Matter = anything with mass and volume.

  • Chemistry studies matter and its properties.

Macroscopic, Microscopic, and Symbolic Domains

  • Macroscopic: what we can see (e.g., water H₂O).

  • Microscopic: particles (atoms, molecules).

  • Symbolic: formulas and equations representing matter.

States and Classification of Matter

  • States: solid, liquid, gas; changes with temperature.

  • Gas is compressible; solid is not.

  • Mass vs Weight: weight depends on gravity; mass is constant.

  • Classification by composition: element, compound, homogeneous mixture, heterogeneous mixture.

Physical vs Chemical Properties and Changes

  • Physical property/change: does not alter composition.

  • Chemical property/change: involves change in composition.

Intensive vs Extensive Properties

  • Intensive: do not depend on amount (e.g., density, temperature, boiling point).

  • Extensive: depend on amount (e.g., mass, length, volume, total energy).

Measurements and Units

  • Measurement involves a quantity with three parts: magnitude, unit, and uncertainty.

  • Base SI units: extLength=extmeter(m),extMass(kg),extTime(s),extTemperature(K),extAmountofsubstance(mol),<br>extElectriccurrent(A),extLuminousintensity(cd)ext{Length} = ext{meter }(m), ext{ Mass }(kg), ext{ Time }(s), ext{ Temperature }(K), ext{ Amount of substance }(mol), <br>ext{ Electric current }(A), ext{ Luminous intensity }(cd)

  • Three basic parts of a quantity: magnitude, unit, and uncertainty.

  • Common length, mass, volume, temperature, and time units.

Temperature Scales and Conversions

  • Celsius (°C), Fahrenheit (°F), Kelvin (K).

  • Conversions:

    • T(K)=t(∘C)+273.15T(K) = t(^{\circ}C) + 273.15

    • from Celsius to Fahrenheit: ∘F=1.8(∘C)+32^{\circ}F = 1.8(^{\circ}C) + 32

  • Absolute zero is 0 K (−273.15 °C).

Density and its Calculation

  • Density is an intensive property: ρ=mV\rho = \frac{m}{V}

  • Temperature affects densities of liquids and gases.

  • Example: mercury has density ρHg=13.6 g/cm3\rho_{Hg} = 13.6\ \text{g/cm}^3 at standard conditions.

Energy and Work

  • Work: W=F⋅dW = F \cdot d

  • Energy: capacity to do work; unit is the Joule: 1 J=1 kg m2 s−21\ \text{J} = 1\ \mathrm{kg\, m^2\, s^{-2}}

Measurement Errors: Precision and Accuracy

  • Random (indeterminate) errors: unpredictable; can be reduced by repeated measurements.

  • Systematic (determinate) errors: bias in one direction; harder to detect.

  • Accuracy: closeness to true value.

  • Precision: closeness of a set of measurements to each other.

Significant Figures and Measurements

  • Significant figures convey measurement precision; rules depend on zeros, decimals, and exact values.

  • Exact values (in definitions or counted values) have infinite sig figs.

  • Examples of exact values: 1 in = 2.54 cm; 1 mole = 6.02×10²³ units.

Dimensional Analysis (Factor-Label Method)

  • Convert units by multiplying by appropriate factors to cancel units and achieve desired units.

  • Example approach: set up conversion factors from known relationships and cancel units progressively.

Metric Prefixes and Derived Units

  • Prefixes (multipliers):

    • kilo (k): 10310^3, mega (M): 10610^6, giga (G): 10910^9, tera (T): 101210^{12}, peta (P): 101510^{15}, exa (E): 101810^{18}

    • deci (d): 10−110^{-1}, centi (c): 10−210^{-2}, milli (m): 10−310^{-3}, micro (\mu): 10−610^{-6}, nano (n): 10−910^{-9}, pico (p): 10−1210^{-12}, femto (f): 10−1510^{-15}, atto (a): 10−1810^{-18}

  • Derived units: speed speed=distancetime\text{speed} = \frac{\text{distance}}{\text{time}}; volume V=length×width×height=m3V = \text{length} \times \text{width} \times \text{height} = \text{m}^3; 1\ \text{m}^3 = 1000\ \text{L}</p></li></ul><h3collapsed="false"seolevelmigrated="true">DimensionalAnalysis:PracticeandApplications</h3><ul><li><p>Practiceproblemsillustrateconvertingbetweenunits(e.g.,volumetomassviadensity;distancetovelocity;energyunits).</p></li></ul><h3collapsed="false"seolevelmigrated="true">QuantitativevsQualitativeObservations</h3><ul><li><p>Qualitative:descriptive(color,state).</p></li><li><p>Quantitative:measurementswithnumbersandunits.</p></li></ul><h3collapsed="false"seolevelmigrated="true">DimensionalConsistencyandCalculations</h3><ul><li><p>Useconsistentunitsthroughoutcalculations;reportfinalanswerswithappropriatesignificantfigures.</p></li></ul><h3collapsed="false"seolevelmigrated="true">QuickReference:KeyEquations</h3><ul><li><p>Density:</p></li></ul><h3 collapsed="false" seolevelmigrated="true">Dimensional Analysis: Practice and Applications</h3><ul><li><p>Practice problems illustrate converting between units (e.g., volume to mass via density; distance to velocity; energy units).</p></li></ul><h3 collapsed="false" seolevelmigrated="true">Quantitative vs Qualitative Observations</h3><ul><li><p>Qualitative: descriptive (color, state).</p></li><li><p>Quantitative: measurements with numbers and units.</p></li></ul><h3 collapsed="false" seolevelmigrated="true">Dimensional Consistency and Calculations</h3><ul><li><p>Use consistent units throughout calculations; report final answers with appropriate significant figures.</p></li></ul><h3 collapsed="false" seolevelmigrated="true">Quick Reference: Key Equations</h3><ul><li><p>Density:\rho = \frac{m}{V}</p></li><li><p>Massviadensity:</p></li><li><p>Mass via density:m = \rho V</p></li><li><p>Weight:</p></li><li><p>Weight:W = m g</p></li><li><p>Energy/Work:</p></li><li><p>Energy/Work:J = \mathrm{kg\, m^2\, s^{-2}}</p></li><li><p>Temperatureconversions:</p></li><li><p>Temperature conversions:T(K) = t(^{\circ}C) + 273.15,\quad ^{\circ}F = 1.8(^{\circ}C) + 32</p></li><li><p>Speed:</p></li><li><p>Speed:\text{speed} = \frac{\text{distance}}{\text{time}}</p></li><li><p>Volume:</p></li><li><p>Volume:V = \text{length} \times \text{width} \times \text{height} = \text{m}^3,\quad 1\ \text{m}^3 = 1000\ \text{L}$$

  • Derived units and common conversions are based on the SI system above.

Observations and Data Types

  • Observations/data are used to formulate hypotheses, theories, and laws.

  • Distinguish between measurement types (qualitative vs quantitative) and ensure units and uncertainties are reported.

Quick Facts for Last-Minute Review

  • Matter states and compressibility: gas compressible; solid incompressible.

  • Major classifications: element, compound, homogeneousmixture, heterogeneous mixture.

  • Distinguish physical vs chemical properties and changes.

  • Distinguish intensive vs extensive properties.

  • Understand the role of measurement uncertainty and rounding rules when reporting results.

  • Master the use of dimensional analysis for unit conversions.