CHEM 170 Exam 1 Study Guide: Foundations of Chemistry

The Chemical World

Chemicals in Everyday Life

Chemicals are the substances that make up everything we encounter in our world, from the air we breathe to the food we eat. Understanding their properties and interactions is fundamental to chemistry.

• Chemicals are defined as substances with a definite composition.

• Examples: Water (H2O), table salt (NaCl), and carbon dioxide (CO2).

The Scientific Method

The scientific method is a systematic approach used to investigate natural phenomena and develop new knowledge.

• Observation: Gathering information through the senses.

• Hypothesis: A tentative explanation for an observation.

• Experimentation: Testing hypotheses through controlled experiments.

• Laws: Statements that summarize experimental results.

• Theories: Explanations that unify laws and observations.

Interpreting Data and Graphs

Identifying patterns in data and interpreting graphs is essential for understanding chemical phenomena.

• Graphs visually represent relationships between variables.

• Patterns help predict outcomes and understand trends.

Measurement and Problem Solving

Scientific Notation

Scientific notation is used to express very large or very small numbers in a concise form.

• Example: $6.02 \times 10^{23}$ (Avogadro's number).

• Format: $a \times 10^n$ where $a$ is a number between 1 and 10, and $n$ is an integer.

Significant Figures

Significant figures reflect the precision of a measured quantity.

• All nonzero digits are significant.

• Zeros between nonzero digits are significant.

• Trailing zeros in a decimal number are significant.

Rounding and Calculations

Numbers are rounded to the correct number of significant figures after calculations.

• Multiplication/Division: Round to the least number of significant figures.

• Addition/Subtraction: Round to the least number of decimal places.

Metric (SI) Units and Prefixes

The metric system uses standard units and prefixes to measure quantities.

• Length: meter (m)

• Mass: kilogram (kg)

• Time: second (s)

• Prefixes: kilo- ($10^3$), centi- ($10^{-2}$), milli- ($10^{-3}$)

Dimensional Analysis and Unit Conversions

Dimensional analysis uses conversion factors to change units between metric and English systems.

• Example: $1 \text{ mile} = 1.609 \text{ kilometer}$

• Conversion factors are ratios used to multiply and cancel units.

Density Calculations

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

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

• Units: g/cm3 or kg/m3

• Used as a conversion factor between mass and volume.

Matter and Energy

Definitions: Matter, Atoms, Molecules

Matter is anything that has mass and occupies space. Atoms are the basic units of matter, and molecules are combinations of atoms.

• Matter: Anything with mass and volume.

• Atom: Smallest unit of an element.

• Molecule: Two or more atoms bonded together.

States of Matter

Matter exists in three primary states: solid, liquid, and gas.

• Solid: Definite shape and volume.

• Liquid: Definite volume, indefinite shape.

• Gas: Indefinite shape and volume.

Classification of Matter

Matter can be classified as elements, compounds, or mixtures.

• Element: Pure substance made of one type of atom.

• Compound: Substance made of two or more elements chemically bonded.

• Mixture: Combination of two or more substances not chemically bonded.

• Homogeneous mixture: Uniform composition.

• Heterogeneous mixture: Non-uniform composition.

Physical vs. Chemical Properties

Physical properties can be observed without changing the substance, while chemical properties describe how a substance reacts.

• Physical properties: Color, density, melting point.

• Chemical properties: Reactivity, flammability.

Physical vs. Chemical Changes

Physical changes alter the form but not the identity of a substance; chemical changes produce new substances.

• Physical change: Melting, boiling, dissolving.

• Chemical change: Burning, rusting.

Temperature and Scales

Temperature measures the average kinetic energy of particles. Three scales are used: Celsius, Fahrenheit, and Kelvin.

• Celsius (°C): Water freezes at 0°C, boils at 100°C.

• Fahrenheit (°F): Water freezes at 32°F, boils at 212°F.

• Kelvin (K): Absolute zero is 0 K.

Atoms and Elements

Atomic Theory

All matter is composed of atoms. Atomic theory explains the structure and behavior of atoms.

• Atoms are indivisible particles.

• Atoms of the same element are identical.

• Atoms combine to form compounds.

Nuclear Theory of the Atom

The nuclear theory describes the atom as having a dense nucleus containing protons and neutrons, surrounded by electrons.

• Nucleus: Contains protons and neutrons.

• Electrons: Orbit the nucleus.

Subatomic Particles

Atoms are made of protons, neutrons, and electrons, each with distinct properties.

• Proton: Positive charge, located in nucleus.

• Neutron: No charge, located in nucleus.

• Electron: Negative charge, orbits nucleus.

Atomic Symbols and Numbers

Each element has a unique atomic symbol and number, which can be found on the periodic table.

• Atomic number (Z): Number of protons.

• Atomic mass: Weighted average mass of isotopes.

Periodic Table Classification

The periodic table organizes elements by increasing atomic number and groups them by similar properties.

• Groups: Columns with similar properties.

• Metals: Conductive, malleable.

• Nonmetals: Insulating, brittle.

• Metalloids: Properties intermediate between metals and nonmetals.

Isotopes and Mass Notation

Isotopes are atoms of the same element with different numbers of neutrons. Mass notation is used to represent isotopes.

• Isotope: Same atomic number, different mass number.

• Mass number (A): Sum of protons and neutrons.

• Isotope notation: Element-A or AElement

Average Atomic Mass Calculation

The average atomic mass is calculated using the fractional abundance and mass of each isotope.

• Formula: $\text{AM} = f_1M_1 + f_2M_2 + \ldots + f_nM_n$

• AM: Average atomic mass

• fn: Fractional percent of the isotope

• M: Mass of the isotope

Chemical Composition

The Mole Concept

The mole is a counting unit used to relate the mass of a substance to the number of particles.

• 1 mole: $6.022 \times 10^{23}$ particles (Avogadro's number)

• Used to convert between grams, moles, and number of atoms/molecules.

Dimensional Analysis for Chemical Quantities

Dimensional analysis is used to convert between mass, moles, and number of particles using conversion factors.

• Example: $\text{grams} \rightarrow \text{moles} \rightarrow \text{atoms}$

• Conversion factors: Molar mass, Avogadro's number.

Electrons in Atoms and the Periodic Table

Electromagnetic Radiation and Energy

Electromagnetic radiation (light) has different types and energies, which affect atomic behavior.

• Types: Gamma rays, X-rays, UV, visible, IR, microwaves, radio waves.

• Energy increases with frequency.

Bohr Model of the Atom

The Bohr model describes electrons in fixed orbits around the nucleus, each with specific energy levels.

• Electrons move between orbits by absorbing or emitting energy.

Quantum-Mechanical Model

The quantum-mechanical model describes electrons as occupying orbitals, regions of space with a high probability of finding an electron.

• Orbitals: s, p, d, f

• Electron configuration shows how electrons are distributed among orbitals.

Electron Configurations and Orbital Diagrams

Electron configurations and orbital diagrams represent the arrangement of electrons in an atom.

• Example: $1s^2 2s^2 2p^6$

• Abbreviated configurations use noble gas notation.

Valence Electrons

Valence electrons are the outermost electrons and determine chemical properties.

• Elements in the same group have the same number of valence electrons.

Chemical Properties and Valence Electrons

The chemical properties of elements are largely determined by their valence electrons.

• Elements with similar valence electron counts behave similarly.

Periodic Trends

Periodic trends describe how properties change across the periodic table.

• Atomic size: Increases down a group, decreases across a period.

• Ionization energy: Decreases down a group, increases across a period.

• Metallic character: Increases down a group, decreases across a period.

Reference Information

Useful Conversion Factors

• 1 mile = 1.609 kilometer

• 2.2 pounds = 1 kilogram

• Volume of a cube: $a^3$ (where $a$ is the length of a side)

• Volume of a sphere: $\frac{4}{3}\pi r^3$ (where $r$ is the radius)

Sample Electron Configuration

• Example: $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2 4d^{10} 5p^6 6s^2 4f^{14} 5d^{10} 6p^6 7s^2 5f^{14} 6d^{10} 7p^6$

Additional info: Academic context and explanations have been expanded for clarity and completeness based on the study guide topics.