Chapter 1: Chemistry Basics—Matter and Measurement (GOB Chemistry Study Notes)

Chemistry Basics—Matter and Measurement

Classifying Matter: Pure Substance or Mixture

Chemistry begins with understanding the nature of matter, which is anything that occupies space and has mass. Matter can be classified into pure substances and mixtures, each with distinct properties and behaviors.

• Pure Substances: Matter composed of only one type of substance, represented by a single chemical formula or symbol. Pure substances are further classified as elements (e.g., calcium, hydrogen, carbon) or compounds (e.g., water, rust, ibuprofen).

• Mixtures: Combinations of two or more substances that can be separated into their components. Mixtures are classified as homogeneous (uniform composition, e.g., air, coffee) or heterogeneous (non-uniform composition, e.g., vegetable soup, chocolate chip cookies).

• Atoms: The smallest unit of matter retaining unique properties.

Example: Gold is a pure substance (element), coffee is a homogeneous mixture, table salt is a pure substance (compound), and vegetable soup is a heterogeneous mixture.

Elements, Compounds, and the Periodic Table

The periodic table organizes all known elements, providing information about their properties and relationships. Elements are represented by chemical symbols, often derived from their English or Latin names (e.g., Na for sodium, Au for gold).

• Groups: Vertical columns containing elements with similar chemical behaviors. Main-group elements are designated with 'A', transition elements with 'B', and IUPAC numbering uses 1–18.

• Periods: Horizontal rows numbered 1–7. Sections of periods 6 and 7 are set apart at the bottom.

• Metals, Nonmetals, Metalloids: The staircase line separates metals from nonmetals; elements bordering the line (except Al) are metalloids.

• Biologically Essential Elements: Carbon, hydrogen, oxygen, and nitrogen are most abundant in biological molecules. Macronutrients (needed >100 mg/day) include sodium, magnesium, potassium, calcium, and chlorine. Micronutrients (needed <100 mg/day) include iodine, fluorine, iron, zinc, etc.

• Compounds: Pure substances containing two or more chemically combined elements in specific ratios, represented by chemical formulas (e.g., H2O, NaCl).

How Matter Changes: Physical and Chemical Changes

Matter can undergo changes that alter its form or identity. These changes are classified as physical or chemical.

• Physical Change: Alters the state or appearance of matter without changing its chemical identity (e.g., melting ice to water).

• Chemical Change: Results in a new chemical identity, known as a chemical reaction (e.g., burning charcoal to produce carbon dioxide).

• Chemical Equations: Represent chemical reactions, showing reactants, products, and their physical states (s, l, g, aq).

• Balancing Equations: The number of atoms must be equal on both sides, illustrating the law of conservation of mass. Coefficients are used to balance equations.

Example: Balancing the reaction $\mathrm{CH_4 + 2 O_2 \rightarrow CO_2 + 2 H_2O}$ ensures equal numbers of C, H, and O atoms on both sides.

Math Counts: Measurement and Calculations in Chemistry

Accurate measurement and calculation are fundamental in chemistry. The SI (metric) system is used for consistency.

• SI Units: Mass (kilogram, kg), volume (liter, L), length (meter, m).

• Prefixes: Modify units by powers of ten (e.g., kilo-, milli-, micro-).

• Conversion Factors: Used to convert between units (e.g., $1\ \mathrm{mg} = 1 \times 10^{-3}\ \mathrm{g}$).

• Dimensional Analysis: Method for converting units using conversion factors.

• Significant Figures: Digits known with certainty plus one estimated digit; rules for zeros and rounding apply.

• Scientific Notation: Expresses numbers as $C \times 10^n$, where $C$ is the coefficient and $n$ is the exponent.

• Percent: Represents a part per hundred; calculated as $\frac{\text{part}}{\text{whole}} \times 100$.

Example: $10,000\ \mathrm{cg} \times \frac{1 \times 10^{-2}\ \mathrm{g}}{1\ \mathrm{cg}} = 100\ \mathrm{g}$

Matter: The “Stuff” of Chemistry

Understanding mass, volume, density, and specific gravity is essential for quantifying matter.

• Mass: Amount of material in an object, measured in grams (g).

• Volume: Space occupied by matter, measured in milliliters (mL) or cubic centimeters (cm3).

• Density: Ratio of mass to volume, $d = \frac{m}{V}$; used as a conversion factor.

• Specific Gravity: Ratio of sample density to water density; unitless.

• Temperature: Measured in Fahrenheit (°F), Celsius (°C), and Kelvin (K); conversions: $\mathrm{C} = \frac{\mathrm{F} - 32}{1.8}$, $\mathrm{K} = \mathrm{C} + 273$.

• States of Matter: Solid (definite shape/volume), liquid (definite volume, shape of container), gas (fills container, no definite shape/volume).

Example: Density of gold brick: $d = \frac{1100\ \mathrm{g}}{85\ \mathrm{mL}} = 13\ \mathrm{g/mL}$

Measuring Matter: Accuracy, Precision, and Health Applications

Measurement in chemistry and health requires both accuracy (closeness to true value) and precision (repeatability). SI and U.S. customary units are used, and conversion factors are essential for dosing and health calculations.

• Accuracy: Measurements close to the actual value.

• Precision: Measurements consistent with each other.

• Unit Conversions: Essential for health professionals (e.g., 1 kg = 2.205 lb).

• Dosing Calculations: Use conversion factors to determine correct medication dosages.

• Drop Units: IV medications measured in drops per milliliter (gtt/mL).

• Percents in Health: Used for active ingredient, adult dose, and nutrition labeling.

Example: Acetaminophen dose for a 42 lb child: $7.5\ \mathrm{mg/kg} \times \frac{1\ \mathrm{kg}}{2.2\ \mathrm{lb}} \times 42\ \mathrm{lb} = 140\ \mathrm{mg}$

Summary Table: Properties of States of Matter

Property	Solid	Liquid	Gas
Shape	Definite shape	Adopts shape of container	Adopts shape of container
Volume	Definite volume	Definite volume	Fills volume of container
Kinetic energy	Lowest	Intermediate	Highest
Particle arrangement	Closely packed, fixed	Loosely packed, random	Far apart, random
Attraction between particles	Very strong	Strong	Practically none