Chapter 1: Introduction to Matter and Measurement – General Chemistry Study Notes

Matter and Measurement

Chemistry: The Central Science

Chemistry is the study of the properties and behavior of matter. It is fundamental to understanding many science-related fields, including energy, biochemistry, technology, and medicine.

• Matter is anything that has mass and occupies space.

• Chemistry explores how matter interacts, transforms, and can be measured.

Classification of Matter

Matter can be classified by its state and composition.

States of Matter

• Solid: Definite shape and volume.

• Liquid: Definite volume, shape adapts to container.

• Gas: No definite shape or volume, expands to fill container.

• Example: Water exists as ice (solid), liquid water, and water vapor (gas).

Classification by Composition

Matter is further classified as:

• Pure substances: Uniform composition and distinct properties.

• Mixtures: Composed of two or more substances, properties reflect those of components.

Types of Pure Substances

• Element: Cannot be decomposed into simpler substances.

• Compound: Can be decomposed into simpler substances; consists of two or more elements in fixed proportions.

Types of Mixtures

• Homogeneous mixture (solution): Uniform composition throughout.

• Heterogeneous mixture: Variable composition throughout the sample.

Law of Constant Composition

Compounds have a definite composition, meaning the relative number of atoms of each element is the same in any sample. This is known as the Law of Constant Composition (or Law of Definite Proportions).

Properties of Matter

Physical vs. Chemical Properties

• Physical properties: Can be observed without changing the substance (e.g., boiling point, density, mass, volume).

• Chemical properties: Can only be observed when a substance is changed into another (e.g., flammability, reactivity with acid).

Intensive vs. Extensive Properties

• Intensive properties: Independent of the amount of substance (e.g., density, boiling point, color).

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

Changes in Matter

• Physical changes: Do not alter the composition of a substance (e.g., changes of state, temperature, volume).

• Chemical changes: Result in new substances (e.g., combustion, oxidation, decomposition).

Example: Changes in State

Converting between solid, liquid, and gas is a physical change. For example, melting ice or evaporating water does not change the molecular composition (still H2O).

Chemical Reactions

During a chemical reaction, substances are converted to new substances. For example, hydrogen and oxygen react to form water:

$2H_2 + O_2 \rightarrow 2H_2O$

Separating Mixtures

Mixtures can be separated by exploiting differences in physical properties:

• Filtration: Separates solids from liquids/solutions.

• Distillation: Uses differences in boiling points to separate components of a homogeneous mixture.

• Chromatography: Separates substances based on their ability to adhere to a solid surface.

Measurement in Chemistry

Quantitative Concepts

• Units of measurement

• Measured and calculated quantities

• Uncertainty in measurement

• Significant figures

• Dimensional analysis

SI Units

Physical Quantity	Name of Unit	Abbreviation
Mass	Kilogram	kg
Length	Meter	m
Time	Second	s or sec
Temperature	Kelvin	K
Amount of substance	Mole	mol

Metric System Prefixes

Prefix	Abbreviation	Meaning	Example
Kilo	k	$10^3$	1 kilogram (kg) = $10^3$ grams (g)
Centi	c	$10^{-2}$	1 centimeter (cm) = $10^{-2}$ meters (m)
Milli	m	$10^{-3}$	1 milliliter (mL) = $10^{-3}$ liters (L)
Micro	μ	$10^{-6}$	1 microgram (μg) = $10^{-6}$ grams (g)

Mass, Length, and Volume

• Mass: Amount of material in an object. SI base unit is kilogram (kg); metric system uses gram (g).

• Length: Measure of distance. Base unit is meter (m).

• Volume: Derived from length ($m \times m \times m = m^3$). Common units: liter (L), milliliter (mL), cubic centimeter (cm3).

Temperature

• Celsius scale: Based on water properties. 0°C = freezing point, 100°C = boiling point.

• Kelvin scale: SI unit, based on gases. No negative values; absolute zero is 0 K.

• Conversion: $K = ^\circ C + 273.15$

• Fahrenheit scale: Not used in science. Conversion: $^\circ F = \frac{9}{5}(^\circ C) + 32$ and $^\circ C = \frac{5}{9}(^\circ F - 32)$

Density

• Density is a physical property defined as mass per unit volume.

• Common units: g/mL or g/cm3.

Formula:

$D = \frac{m}{V}$

Numbers in Chemistry

Exact vs. Inexact Numbers

• Exact numbers: Counted or defined (e.g., 12 eggs in a dozen).

• Inexact numbers: Measured, subject to instrument limitations and uncertainty.

Uncertainty in Measurement

• All measurements have some degree of inaccuracy due to instrument limitations.

• Different devices offer different precision and accuracy.

Accuracy vs. Precision

• Accuracy: Closeness of a measurement to the true value.

• Precision: Closeness of repeated measurements to each other.

Significant Figures

• Digits that reflect the precision of a measurement.

• Rules:

  1. All nonzero digits are significant.

  2. Zeroes between significant digits are significant.

  3. Zeroes at the beginning are not significant.

  4. Zeroes at the end are significant if a decimal is present.

• For addition/subtraction: round to the least significant decimal place.

• For multiplication/division: round to the least number of significant figures in any number used.

Dimensional Analysis

• Method for converting one quantity to another using conversion factors.

• Example: $1 \text{ in.} = 2.54 \text{ cm}$

• Set up ratios to cancel units and convert measurements.

Practice and Application

• Exercises on distinguishing elements, compounds, and mixtures.

• Problems involving unit conversions, density calculations, and significant figures.

Example: Calculate the density of a substance with mass 10 g and volume 2 mL:

$D = \frac{10\,g}{2\,mL} = 5\,g/mL$

Example: Convert 25°C to Kelvin:

$K = 25 + 273.15 = 298.15\,K$

Additional info: These notes expand on the provided slides with definitions, examples, and formulas for clarity and completeness.