Introduction to General Chemistry: Classification of Matter, Properties, and Measurement

Intro to General Chemistry

Classification of Matter

Chemistry is the study of matter and the changes it undergoes, with the atom as its basic functional unit. Matter is anything that occupies space and has mass. Matter can be classified into several types based on its composition and properties.

• Pure Substance: A type of matter composed of only one kind of atom or molecule. Examples include elements and compounds.

• Mixture: Matter composed of two or more different elements or compounds that are physically mixed together but not chemically combined. Mixtures can be homogeneous (uniform composition) or heterogeneous (non-uniform composition).

Classification Table:

Type	Definition	Examples
Element	Pure substance of one kind of atom	Oxygen (O2), Gold (Au)
Compound	Pure substance of two or more elements chemically combined	Water (H2O), Sodium chloride (NaCl)
Homogeneous Mixture	Uniform composition throughout	Saltwater, Air
Heterogeneous Mixture	Non-uniform composition	Salad, Sand and iron filings

Example: Crystalline sugar is a pure substance; salsa is a heterogeneous mixture.

Physical and Chemical Changes

Changes in matter can be classified as physical or chemical:

• Physical Change: Alters the state or appearance of matter without changing its composition (e.g., melting ice, dissolving sugar in water).

• Chemical Change: Alters the composition of matter, resulting in new substances with different properties (e.g., burning wood, rusting iron).

Phase Changes: Transitions between solid, liquid, and gas states are physical changes. These can be reversible (e.g., melting and freezing) or irreversible (e.g., burning paper).

Example: Dissolving sugar in water is a physical change; burning wood is a chemical change.

Chemical and Physical Properties

• Chemical Property: Observed when a substance undergoes a chemical reaction (e.g., flammability, reactivity with acids).

• Physical Property: Can be measured without changing the substance's chemical identity (e.g., color, melting point, density).

Example: Mercury is a silvery liquid at 25°C (physical property); sodium reacts violently with water (chemical property).

Intensive vs. Extensive Properties

• Intensive Properties: Do not depend on the amount of substance (e.g., density, boiling point, color).

• Extensive Properties: Depend on the amount of substance (e.g., mass, volume, energy).

Example: Density is intensive; mass is extensive.

Measurement in Chemistry

Temperature and Thermal Energy

• Thermal Energy: The sum of kinetic and potential energies of all atoms in an object.

• Temperature: The average kinetic energy of the particles in a substance.

Temperature is measured in units of Celsius (°C), Kelvin (K), or Fahrenheit (°F).

Temperature Conversion Equations:

• $T_{K} = T_{°C} + 273.15$

• $T_{°F} = \frac{9}{5}T_{°C} + 32$

Scientific Notation

• Used to express very large or very small numbers in a compact form.

• General format: $a \times 10^{n}$, where $1 \leq a < 10$ and $n$ is an integer.

Example: $6,800,000 = 6.8 \times 10^{6}$

SI Units and Metric Prefixes

• The International System of Units (SI) is based on seven base units (meter, kilogram, second, ampere, kelvin, mole, candela).

• Metric prefixes indicate multiples or fractions of base units (e.g., kilo-, centi-, milli-).

Prefix	Symbol	Multiplier
kilo-	k	$10^3$
centi-	c	$10^{-2}$
milli-	m	$10^{-3}$

Significant Figures

• Significant figures are the digits in a measurement that are known with certainty plus one estimated digit.

• Rules for counting significant figures depend on the presence of zeros, decimal points, and scientific notation.

Example: 0.00364 has 3 significant figures.

Precision in Measurement

• When recording measurements, include all certain digits plus one uncertain digit.

• When using instruments, always estimate one digit beyond the smallest marked unit.

Significant Figures in Calculations

• For multiplication/division: The result should have the same number of significant figures as the value with the fewest significant figures.

• For addition/subtraction: The result should have the same number of decimal places as the value with the fewest decimal places.

Conversions and Dimensional Analysis

Conversion Factors

• A conversion factor is a ratio that relates two different units (e.g., $1 \text{ hr} = 60 \text{ min}$).

• Used to convert from one unit to another by multiplying by the appropriate ratio.

Dimensional Analysis

• A systematic approach to problem-solving that uses conversion factors to move from one unit to another.

• Set up the calculation so that units cancel, leaving only the desired unit.

Example: To convert 115 minutes to years, use the chain of conversion factors: $115 \text{ min} \times \frac{1 \text{ hr}}{60 \text{ min}} \times \frac{1 \text{ day}}{24 \text{ hr}} \times \frac{1 \text{ year}}{365 \text{ days}}$

Density and Measurement of Objects

Density

• Density is the amount of mass per unit volume.

Density Formula:

• $\text{Density} = \frac{\text{Mass}}{\text{Volume}}$

Units: $\text{g/cm}^3$ for solids and liquids, $\text{g/L}$ for gases.

Density of Geometric Objects

• For regular shapes, use geometric formulas to find volume, then apply the density formula.

Example: For a cube of side $s$, $V = s^3$.

Density of Non-Geometric Objects: Water Displacement

• For irregular objects, volume can be determined by water displacement (difference in water level before and after submerging the object).

Example: If water rises from 200 mL to 265 mL, the object's volume is $265 - 200 = 65$ mL.

Additional info: These notes cover foundational concepts in general chemistry, including classification of matter, properties, measurement, and basic mathematical operations essential for laboratory and theoretical work.