CHEM 1411: Essential Ideas

Chemistry in Context

• Chemistry: Study of matter's composition, properties, and interactions.

• Historical views: Greeks (four elements), Alchemists (base to noble metals).

• Central Science: Interconnected with many other STEM disciplines.

• Everyday Examples: Digestion, polymer synthesis, oil refining.

The Scientific Method

• Based on observation and experimentation.

• Hypothesis: A tentative explanation of observations.

• Law: Summarizes vast experimental observations, describes/predicts natural phenomena.

• Theory: A well-substantiated, comprehensive, testable explanation of nature.

The Domains of Chemistry

• Macroscopic Domain: Realm of things large enough to be sensed directly.

• Microscopic Domain: Realm of things too small to be sensed directly, visited in imagination or via microscope.

• Symbolic Domain: Specialized language representing macroscopic and microscopic components (e.g., chemical symbols, formulas, equations).

Phases of Matter

• Matter: Anything that occupies space and has mass.

• Common States:

  • Solid: Rigid, definite shape.

  • Liquid: Flows, takes container's shape.

  • Gas: Takes both shape and volume of container.

• Plasma: A fourth state of matter, gaseous with electrically charged particles, found in high-temperature environments (stars, lightning).

Mass vs. Weight

• Mass: Measure of the amount of matter in an object; constant regardless of location.

• Weight: Force gravity exerts on an object; varies with gravitational force.

Law of Conservation of Matter

• No detectable change in total matter quantity when matter converts from one type to another (applies to chemical and physical changes).

Pure Substances and Mixtures

• Pure Substance: Constant composition.

  • Element: Cannot be broken down chemically into simpler substances (e.g., Au, O); consists of one type of atom.

  • Compound: Two or more elements chemically bonded, can be broken down chemically (e.g., $H_2O$); properties differ from constituent elements.

• Mixture: Two or more types of matter, varying amounts, separable by physical changes.

  • Homogeneous Mixture (Solution): Uniform composition, appears visually the same throughout (parts not visible).

  • Heterogeneous Mixture: Composition varies from point to point, visible different parts.

Physical Separation of Mixtures

• Filtration: Separates insoluble solids from liquids.

• Evaporation: Separates a solute from a solvent in a solution.

• Distillation: Separates components based on boiling point differences.

• Separating Funnel: Separates immiscible liquids.

• Chromatography: Separates components based on differential travel across a surface.

• Magnet: Separates magnetic from non-magnetic substances.

• Crystallization: Forms pure solid particles from a solution.

• Floatation: Separates based on density differences.

Atoms and Molecules

• Atom: Smallest particle of an element retaining its properties and capable of chemical combination.

• Molecule: Two or more atoms connected by strong chemical bonds.

Physical and Chemical Properties

• Physical Property: Characteristic not associated with a change in chemical composition (e.g., density, color, melting point, electrical conductivity).

  • Physical Change: Change in state or properties without altering chemical composition (e.g., phase changes like melting/boiling, separating mixtures).

• Chemical Property: Describes how matter changes into another type of matter (e.g., flammability, toxicity, reactivity, heat of combustion).

  • Chemical Change: Process converting one or more substances into new substances (e.g., tarnishing, combustion); signs include bubbles, color/odor change, light/energy output, precipitate formation.

Extensive and Intensive Properties

• Extensive Property: Depends on the amount of matter present (e.g., mass, volume, heat, length).

• Intensive Property: Does not depend on the amount of matter present (e.g., density, temperature).

Measurements

• Scientific Notation: Expressed as $C \times 10^n$, where 1 \le C < 10 and $n$ is an integer.

  • Multiplication: Multiply coefficients, add exponents.

  • Division: Divide coefficients, subtract exponents.

  • Raising to a Power: Raise coefficient to power, multiply exponents.

• Information in a Measurement: A number (magnitude), a unit (standard of comparison), and an indication of uncertainty.

• Units: International System of Units (SI units) is an updated metric system.

  • SI Base Units: Length (meter, m), Mass (kilogram, kg), Time (second, s), Temperature (Kelvin, K), Volume (cubic meter, $m^3$).

Common SI Base Units

• Length: Meter (m).

• Mass: Kilogram (kg).

• Temperature: Kelvin (K) is the SI unit; Celsius ($°C$) is also allowed. $T<em>K = T</em>{°C} + 273.15$.

• Time: Second (s).

Derived SI Units: Volume and Density

• Volume: Amount of space occupied; standard SI unit is cubic meter ($m^3$).

  • $1 dm^3 = 1 L$, $1 cm^3 = 1 mL$.

• Density: Ratio of mass to volume ($density = \frac{mass}{volume}$).

  • Standard SI unit: $kg/m^3$. Common units: $g/cm^3$ (solids/liquids), $g/L$ (gases).

  • Density of water is $1.00 g/mL$ at $4 °C$.

  • Generally, density decreases as temperature increases.

Measurement Uncertainty, Accuracy, and Precision

• Exact Numbers: Obtained by counting or by definition (e.g., $1 ft = 12 in$); free from uncertainty.

• Measured Numbers: Obtained from measuring tools; always have uncertainty, one uncertain digit is estimated.

• Accuracy: How close a measurement is to the true or accepted value.

• Precision: How similar results are when a measurement is repeated.

Significant Figures

• All digits in a measurement, including the uncertain last digit.

• Rules for Significance:

  • Nonzero digits are always significant.

  • Captive zeros (between nonzeros) are significant.

  • Trailing zeros are significant if to the right of the decimal point, or in scientific notation.

  • Leading zeros (left of first nonzero) are not significant.

  • Trailing zeros in a whole number without a decimal point are generally not significant.

Rounding Off Calculated Answers

• If dropped digit < 5: retained numbers remain the same.

• If dropped digit > 5: last retained digit increases by 1.

• If dropped digit = 5: round to the nearest even value for the retained digit.

Significant Figures with Calculations

• Multiplication/Division: Result has the same number of significant figures as the measurement with the fewest significant figures.

• Addition/Subtraction: Result has the same number of decimal places as the measurement with the fewest decimal places.

Mathematical Treatment of Measurement Results

• Dimensional Analysis (Factor-Label Method): Uses conversion factors to relate units and calculate desired quantities.

• Conversion Factor: A ratio of two equivalent quantities expressed with different measurement units (e.g., $rac{2.54 cm}{1 in}$).

Conversion of Temperature Units

• Celsius to Fahrenheit: $T<em>{°F} = (\frac{9}{5} T</em>{°C}) + 32$

• Fahrenheit to Celsius: $T<em>{°C} = \frac{5}{9} (T</em>{°F} - 32)$

• Celsius to Kelvin: $T<em>K = T</em>{°C} + 273.15$

• Kelvin to Celsius: $T<em>{°C} = T</em>K - 273.15$