Chem 101 Exam 1 Study Guide: Chapters 1–4

Elements, Atoms, and Atomic Structure

Atoms vs. Elements

An atom is the smallest unit of matter that retains the properties of an element. An element is a pure substance consisting of only one type of atom, characterized by its atomic number.

• Atom: Basic unit of an element; contains protons, neutrons, and electrons.

• Element: Substance made entirely of one type of atom; defined by atomic number.

• Example: Oxygen (O) is an element; an oxygen atom is a single unit of this element.

Subatomic Particles and Nuclear Model

Atoms are composed of three main subatomic particles:

• Protons: Positively charged, located in the nucleus.

• Neutrons: Neutral, located in the nucleus.

• Electrons: Negatively charged, orbit the nucleus.

Atomic Number, Chemical Symbol, and Atomic Symbols

• Atomic Number (Z): Number of protons in the nucleus; identifies the element.

• Chemical Symbol: One- or two-letter abbreviation for an element (e.g., Na for sodium).

• Full Atomic Symbol: $^{A}_{Z} \text{X}$ where X is the symbol, A is mass number, Z is atomic number.

• Example: $^{23}_{11} \text{Na}$ represents sodium with mass number 23.

Periodic Table Organization and Groups

• Elements are grouped by shared properties.

• Main Groups: 1A (alkali metals), 2A (alkaline earth metals), 7A (halogens), 8A (noble gases).

• Elements classified as metals, nonmetals, or metalloids based on location.

Isotopes, Atomic Number, and Mass Number

• Isotopes: Atoms of the same element with different numbers of neutrons.

• Atomic Number: Number of protons.

• Mass Number: Sum of protons and neutrons.

• Average Atomic Mass: Weighted average based on isotope abundance.

• Formula: $\text{Average Atomic Mass} = \sum (\text{Isotope Mass} \times \text{Fractional Abundance})$

Element Names and Symbols

• Required to know names and symbols for elements 1–30, plus Br, I, Ag, Au, Sn, Pb, Hg, Sr, Ba, Rb, Cs.

Electromagnetic Spectrum, Electron Configuration, and Periodic Trends

Electromagnetic Radiation: Wavelength, Energy, Frequency

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

• Relationship: $E = h\nu$ and $c = \lambda\nu$

• Energy: Higher frequency means higher energy.

• Example: X-rays have higher energy than UV light.

White Light vs. Atomic Line Spectrum

• White Light: Contains all wavelengths; produces a continuous spectrum.

• Atomic Line Spectrum: Discrete lines; each corresponds to a specific electron transition.

• Line Spectra: Emission of light at specific wavelengths by excited atoms.

Bohr Atom and Electron Transitions

• Bohr Model: Electrons occupy fixed orbits with quantized energy levels.

• Quantum Number (n): Specifies energy level.

• Excited State: Electron at higher energy level.

• Ground State: Electron at lowest energy level.

• Electron Transitions: Movement between energy levels emits or absorbs light.

Quantum Mechanical Model

• Electrons occupy orbitals defined by quantum numbers.

• Principal Quantum Number (n): Main energy level/shell.

• Sublevels: s, p, d, f.

• Number of Orbitals: s (1), p (3), d (5), f (7).

• Electrons per Sublevel: s (2), p (6), d (10), f (14).

• Orbital Shapes: s (sphere), p (dumbbell), d (cloverleaf).

Electron Configurations

• Full Configuration: Lists all occupied orbitals starting with 1s.

• Condensed Configuration: Uses noble gas core.

• Valence Orbital Diagram: Shows valence electrons.

• Core vs. Valence Electrons: Core are inner electrons; valence are outermost.

Lewis Dot Symbols, Cations, and Anions

• Lewis Dot Symbol: Shows valence electrons as dots around element symbol.

• Cation: Formed by loss of electrons (positive charge).

• Anion: Formed by gain of electrons (negative charge).

• Predicting Ions: Main group elements form ions to achieve noble gas configuration.

Periodic Trends

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

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

• Ionization Energy: Energy required to remove an electron; increases across a period.

• Electron Affinity: Tendency to gain an electron; increases across a period.

Compounds and Formulas

Classification of Matter

• Element: Pure substance of one type of atom.

• Compound: Substance of two or more elements chemically combined.

• Mixture: Physical combination of elements and/or compounds.

• Heterogeneous Mixture: Non-uniform composition.

• Homogeneous Mixture: Uniform composition.

Phases of Matter

• Solid: Definite shape and volume.

• Liquid: Definite volume, indefinite shape.

• Gas: Indefinite shape and volume.

Chemical vs. Physical Properties/Changes

• Chemical Property: Ability to undergo chemical change (e.g., reactivity).

• Physical Property: Observable without changing composition (e.g., melting point).

• Chemical Change: Produces new substances.

• Physical Change: Alters form, not composition.

Formulas for Compounds

• Binary Ionic Compound: Combination of cation and anion.

• Ionic Compound: Metal + nonmetal; may contain polyatomic ions.

• Molecular Compound: Nonmetal + nonmetal.

• Acid: Compound that releases H+ in water.

• Formula Writing: Combine ions to balance charges.

Naming Compounds

• Binary Molecular: Use prefixes (mono-, di-, etc.) and element names.

• Binary Ionic: Name cation, then anion; variable charge cations use Roman numerals.

• Polyatomic Ions: Memorize ammonium, hydroxide, acetate, carbonate, nitrite, nitrate, phosphate, sulfate, perchlorate.

• Acids: Simple acids (hydrochloric acid), oxo acids (sulfuric acid).

Table: Common Polyatomic Ions

Ion Name	Formula
Ammonium	NH4+
Hydroxide	OH-
Acetate	CH3COO-
Carbonate	CO32-
Nitrite	NO2-
Nitrate	NO3-
Phosphate	PO43-
Sulfate	SO42-
Perchlorate	ClO4-

Measurements and Conversions

SI Base Units and Metric Prefixes

• Mass: kilogram (kg)

• Length: meter (m)

• Time: second (s)

• Temperature: kelvin (K)

• Common Metric Prefixes: kilo-, centi-, milli-, micro-, nano-, etc.

Temperature Conversions

• Celsius to Kelvin: $K = ^\circ C + 273.15$

• Kelvin to Celsius: $^\circ C = K - 273.15$

Scientific Notation

• Expresses very large or small numbers as $a \times 10^n$.

• Used to simplify calculations and comparisons.

Significant Figures

• Significant Figures: Digits that represent measured values.

• Rules: All nonzero digits are significant; zeros between nonzero digits are significant; leading zeros are not significant; trailing zeros are significant if after a decimal.

• Exact Numbers: Have infinite significant figures (e.g., counting numbers).

Calculations with Significant Figures

• Addition/Subtraction: Result has same decimal places as least precise measurement.

• Multiplication/Division: Result has same number of significant figures as measurement with fewest significant figures.

Metric Conversions

• Convert between units using metric prefixes.

• One-step and two-step conversions may be required.

Density Calculations

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

• Used as a conversion factor in calculations.

• Example: If mass = 10 g and volume = 2 mL, density = 5 g/mL.

Study Strategies and Resources

• Review ALEKS topics and assignments.

• Use posted reference materials and periodic table during practice.

• Master key equations and skills at the end of each chapter.

• Practice textbook problems (suggested problems listed for each chapter).

• Redo worksheet and lecture problems.

• Attend office hours and drop-in sessions for help.

• Form study groups for collaborative learning.

Exam Format and Guidelines

• Exam includes multiple choice, fill-in-the-blank, and show-your-work problems.

• Show all work, including units and labels, for partial credit.

• No outside materials or smart devices allowed.

• Reference sheets and periodic table provided.

• Follow academic integrity guidelines.