CHEM 108 Exam 1 Study Guide: Foundations of Chemistry, Atomic Structure, and the Periodic Table

Classification and Properties of Matter

Types of Matter

Matter can be classified based on its composition and uniformity. Understanding these classifications is fundamental to chemistry.

• Pure Substances: Have a fixed composition and distinct properties. Examples include elements (e.g., O2, Fe) and compounds (e.g., H2O, NaCl).

• Mixtures: Combinations of two or more substances that retain their individual properties. Mixtures can be:

  • Homogeneous Mixtures (Solutions): Uniform composition throughout (e.g., saltwater).

  • Heterogeneous Mixtures: Non-uniform composition (e.g., salad, sand in water).

Example: Air is a homogeneous mixture, while a salad is a heterogeneous mixture.

Physical and Chemical Properties

Properties of matter are categorized based on whether they involve a change in composition.

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

• Chemical Properties: Describe a substance's ability to undergo changes that transform it into different substances (e.g., flammability, reactivity).

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

• Intensive Properties: Independent of the amount of matter (e.g., density, boiling point).

Example: Density is an intensive property; mass is an extensive property.

Physical vs. Chemical Change

• Physical Change: Alters appearance but not composition (e.g., melting ice).

• Chemical Change: Produces new substances (e.g., burning wood).

Conservation Laws

• Law of Conservation of Matter: Matter is neither created nor destroyed in a chemical reaction.

• Law of Conservation of Energy: Energy cannot be created or destroyed, only transformed.

Measurement and Calculations in Chemistry

SI Units and Metric Prefixes

Chemists use the International System of Units (SI) for measurements. Prefixes indicate powers of ten.

• Milli- (m): $10^{-3}$

• Kilo- (k): $10^{3}$

• Other prefixes range from $10^{9}$ (giga-) to $10^{-9}$ (nano-).

Unit Conversions and Dimensional Analysis

• Use conversion factors to change units (e.g., $1\ \text{kg} = 1000\ \text{g}$).

• Dimensional analysis ensures units cancel appropriately.

Example: To convert 5 km to meters: $5\ \text{km} \times \frac{1000\ \text{m}}{1\ \text{km}} = 5000\ \text{m}$

Volume and Density Calculations

• Volume of a Cube: $V = a^3$ (where $a$ is the length of a side)

• Volume of a Cylinder: $V = \pi r^2 h$

• Volume of a Sphere: $V = \frac{4}{3} \pi r^3$

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

Example: If a cube has sides of 2 cm, $V = (2\ \text{cm})^3 = 8\ \text{cm}^3$.

Scientific Notation and Significant Figures

• Scientific notation expresses numbers as $a \times 10^n$.

• Significant figures reflect the precision of a measurement.

• Answers to calculations must have the correct number of significant figures and units.

Example: $0.00045$ in scientific notation is $4.5 \times 10^{-4}$.

Accuracy vs. Precision

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

• Precision: How close repeated measurements are to each other.

Atomic Structure and the Periodic Table

Atomic Symbols and Isotopes

• Each element is represented by a unique symbol (e.g., H for hydrogen, Fe for iron).

• Atomic number ($Z$): Number of protons.

• Mass number ($A$): Number of protons + neutrons.

• Isotope Symbol: $^{A}_{Z}\text{X}$, where X is the element symbol.

Example: $^{14}_{6}\text{C}$ is a carbon isotope with 6 protons and 8 neutrons.

Structure of the Atom

• Atoms consist of a nucleus (protons and neutrons) and electrons in surrounding orbitals.

• Electrons are negatively charged, protons are positive, neutrons are neutral.

Calculating Atomic Weight

• Atomic weight is the weighted average of isotopic masses based on natural abundance.

Formula: $\text{Atomic Weight} = \sum (\text{Isotopic Mass} \times \text{Fractional Abundance})$

The Periodic Table

• Elements are arranged by increasing atomic number.

• Periods: Horizontal rows.

• Groups (Columns): Vertical columns with similar properties.

• Special Groups:

  • Alkali Metals: Group 1

  • Alkaline Earth Metals: Group 2

  • Coinage Metals: Group 11 (Cu, Ag, Au)

  • Halogens: Group 17

  • Noble Gases: Group 18

The Mole and Dimensional Analysis

The Mole Concept

• One mole contains $6.022 \times 10^{23}$ entities (Avogadro's number).

• Used to relate mass, number of particles, and volume in chemical calculations.

Example: 1 mole of H2O contains $6.022 \times 10^{23}$ molecules.

Dimensional Analysis

• Systematic approach to problem-solving using conversion factors.

• Ensures correct units and significant figures in calculations.

Electromagnetic Radiation and Atomic Models

Wavelength, Frequency, and the Speed of Light

• Electromagnetic radiation is characterized by its wavelength ($\lambda$) and frequency ($\nu$).

• They are related by the speed of light ($c$):

$c = \lambda \nu$

Where $c = 2.998 \times 10^8\ \text{m/s}$

• Different types of electromagnetic radiation have different wavelengths and frequencies (e.g., gamma rays, X-rays, UV, visible, IR, microwaves, radio waves).

Dual Nature of Light

• Light exhibits both wave-like and particle-like properties.

• Key experiments: Photoelectric effect (particle nature), diffraction (wave nature).

Energy of a Photon

• The energy ($E$) of a photon is proportional to its frequency and inversely proportional to its wavelength:

$E = h \nu$

Where $h$ is Planck's constant ($6.626 \times 10^{-34}\ \text{J} \cdot \text{s}$)

$\lambda = \frac{c}{\nu}$

Atomic Models and Electron Configuration

The Bohr Model of the Atom

• Electrons orbit the nucleus in fixed energy levels.

• Explains line spectra of hydrogen but not more complex atoms.

Orbit vs. Orbital

• Orbit: Fixed path in Bohr model.

• Orbital: Region of space with high probability of finding an electron (quantum model).

Pauli Exclusion Principle

• No two electrons in an atom can have the same set of four quantum numbers.

Aufbau Principle and Hund’s Rule

• Aufbau Principle: Electrons fill orbitals in order of increasing energy.

• Hund’s Rule: Electrons occupy degenerate orbitals singly before pairing up, maximizing unpaired electrons with parallel spins.

Electron Configuration

• Describes the arrangement of electrons in an atom.

• Uses spdf notation and noble gas shorthand.

• Example for oxygen: 1s2 2s2 2p4

• Valence electrons are in the outermost shell; core electrons are in inner shells.

Orbital Diagrams

• Visual representations of electron configurations using arrows for electrons and boxes/lines for orbitals.

Effective Nuclear Charge and Atomic Radii

• Effective Nuclear Charge (Zeff): The net positive charge experienced by valence electrons.

• Increases across a period, causing atomic radii to decrease.

Table: Common SI Prefixes

Prefix	Symbol	Factor
kilo-	k	$10^{3}$
milli-	m	$10^{-3}$
nano-	n	$10^{-9}$
giga-	G	$10^{9}$
centi-	c	$10^{-2}$
micro-	\mu	$10^{-6}$

Table: Selected Groups of the Periodic Table

Group Name	Group Number	Example Elements
Alkali Metals	1	Li, Na, K
Alkaline Earth Metals	2	Mg, Ca
Coinage Metals	11	Cu, Ag, Au
Halogens	17	F, Cl, Br, I
Noble Gases	18	He, Ne, Ar

Additional info: Some explanations and examples have been expanded for clarity and completeness, as is standard in academic study guides.