Intro to General Chemistry

Classification of Matter

Understanding the difference between elements, compounds, and mixtures is foundational in chemistry. Elements are pure substances consisting of only one type of atom, while compounds are substances formed from two or more elements chemically bonded in fixed proportions.

• Element: A substance that cannot be broken down into simpler substances by chemical means.

• Compound: A substance composed of two or more elements chemically combined.

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

• Example: Water (H2O) is a compound; oxygen (O2) is an element.

Physical and Chemical Properties & Changes

Physical vs. Chemical Processes

Physical changes affect the form of a substance, not its chemical identity. Chemical changes result in the formation of new substances.

• Physical Process: Change in state (e.g., melting ice cube), shape, or appearance without altering chemical composition.

• Chemical Process: Change that produces new substances (e.g., reaction of uranium with cold water).

• Example: Melting an ice cube is a physical process; rusting iron is a chemical process.

Physical and Chemical Properties

Properties are characteristics used to identify substances. Physical properties can be observed without changing the substance, while chemical properties describe a substance's ability to undergo chemical changes.

• Physical Properties: Color, density, melting point, boiling point, luster, malleability.

• Chemical Properties: Reactivity with water, acid, or other chemicals; flammability; ability to oxidize.

• Example Table:

Measurement and Units

Extensive vs. Intensive Properties

Properties of matter are classified as extensive or intensive. Extensive properties depend on the amount of substance, while intensive properties do not.

• Extensive Properties: Volume, mass, length.

• Intensive Properties: Temperature, density, concentration, hardness, luster.

• Example: Volume is extensive; temperature is intensive.

Temperature Conversions

Temperature can be measured in Celsius, Fahrenheit, or Kelvin. The Kelvin scale is the SI unit for temperature.

• Conversion Formula:

• To convert from Fahrenheit to Kelvin:

• Example: 13°F = K

Scientific Notation

Scientific notation expresses numbers as a product of a coefficient and a power of ten.

• Format:

• Increasing coefficient: Exponent decreases.

• Decreasing coefficient: Exponent increases.

• Example: has 3 significant figures.

SI Units and Prefixes

SI units are the standard units for scientific measurements. Prefixes indicate multiples or fractions of units.

• Kinetic Energy Formula:

• Common SI prefixes: kilo (k, ), mega (M, ), milli (m, ), micro (, ), pico (p, )

• Example: 513 mK/s = K/s

Significant Figures

Significant figures reflect the precision of a measurement. The rules for determining significant figures depend on the type of operation performed.

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

• Addition/Subtraction: Result has the same number of decimal places as the measurement with the fewest decimal places.

• Example: 780 + 6.97 - 81.197 = 705.77 (rounded to two decimal places)

Chemical Quantities & Calculations

Density and Mass Calculations

Density is defined as mass per unit volume. It is used to identify substances and convert between mass and volume.

• Density Formula:

• Volume of a Sphere:

• Example: For a sphere with diameter 3.95 cm, cm,

Unit Conversions

Unit conversions are essential for expressing measurements in appropriate SI units.

• Example: Converting micrograms per cubic meter (g/m3) to grams for a given volume.

Atoms & Elements

Atomic Symbols and Isotopes

Elements are represented by symbols, and isotopes are atoms of the same element with different numbers of neutrons.

• Atomic Symbol: where A = mass number, Z = atomic number, X = element symbol.

• Isotope Example: Cl and Cl are isotopes of chlorine.

• Calculating Isotopic Abundance: Weighted average based on natural abundance.

Classification of Elements

Elements are classified as metals, nonmetals, and metalloids based on their properties.

• Metals: Good conductors, malleable, ductile.

• Nonmetals: Poor conductors, brittle, varied states.

• Metalloids: Properties intermediate between metals and nonmetals.

Periodic Table Groups

Elements are grouped in the periodic table based on similar properties.

• Alkali Metals: Group 1A

• Alkaline Earth Metals: Group 2A

• Halogens: Group 7A

• Noble Gases: Group 8A

Main-Group vs. Transition Elements

Main-group elements are found in groups 1A-8A, while transition metals are in the center of the periodic table.

• Main-group elements: Groups 1A-8A

• Transition metals: Groups 3B-12B

• Example: Vanadium is a transition metal, not a main-group element.

Chemical Reactions & Molecular Views

Acid-Base Reactions

Acid-base reactions involve the transfer of protons between reactants, often producing a salt and water.

• General Reaction:

• Example: HCl + NaOH → NaCl + H2O

Molecular Representations

Molecular-level views help visualize the arrangement of atoms and molecules in elements and compounds.

• Atomic Element: Individual atoms (e.g., triangles for X).

• Diatomic Element: Molecules composed of two atoms (e.g., squares for Y).

Additional Info

• Some elements exist only as solids at standard conditions (e.g., iron, copper).

• Significant figures are crucial for reporting scientific measurements accurately.

• Unit conversions and dimensional analysis are essential skills in laboratory and theoretical chemistry.