Classification and Properties of Matter

Elements, Compounds, and Mixtures

Matter can be classified as elements, compounds, or mixtures based on its composition and properties.

• Element: A pure substance consisting of only one type of atom (e.g., O2, Fe).

• Compound: A substance formed from two or more elements chemically combined in fixed proportions (e.g., H2O, NaCl).

• Mixture: A physical combination of two or more substances where each retains its own properties (e.g., air, saltwater).

Example: In a reaction where two unknown liquids form a solid and another liquid, we cannot determine if the substances are elements or compounds solely from the reaction type.

Physical vs. Chemical Properties and Changes

Properties and changes of matter are classified as physical or chemical:

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

• Chemical Property: Describes a substance's ability to undergo a specific chemical change (e.g., reactivity with water, flammability).

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

• Chemical Change: Results in the formation of new substances (e.g., rusting iron).

Example: Melting an ice cube is a physical process because it changes state from solid to liquid without altering the chemical identity (H2O).

Example: Reacting uranium with cold water is a chemical property, while its color or density are physical properties.

Classification Table: Physical vs. Chemical Properties

Extensive vs. Intensive Properties

Properties of matter are also classified as:

• Extensive Property: Depends on the amount of substance (e.g., mass, volume).

• Intensive Property: Independent of the amount of substance (e.g., density, temperature, color).

Example: Volume is an extensive property, while temperature is intensive.

Measurement and Units in Chemistry

Temperature Scales and Conversions

Temperature can be measured in Celsius (°C), Fahrenheit (°F), or Kelvin (K). The Kelvin scale is the SI unit for temperature.

• Conversion from Fahrenheit to Kelvin:

Example: 13°F = 263 K (rounded to the nearest whole number).

Scientific Notation and Significant Figures

• Scientific Notation: Expresses numbers as a product of a coefficient and a power of ten (e.g., ).

• Significant Figures: Digits in a measurement that are known with certainty plus one estimated digit.

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

Example: has 3 significant figures.

SI Units and Prefixes

• Base SI Units: meter (m), kilogram (kg), second (s), kelvin (K), mole (mol), ampere (A), candela (cd).

• Common Prefixes: kilo- (k, ), milli- (m, ), micro- (μ, ), nano- (n, ).

Example: 513 mK/s = 0.513 K/s.

Derived Units and Kinetic Energy

Kinetic energy in classical mechanics is given by:

• Unit of Energy: Joule (J), where .

• SI Prefixes: kJ (kilojoule), MJ (megajoule), pJ (picojoule), etc.

Example: For a car, kJ or MJ may be convenient; for an electron, pJ or fJ may be appropriate.

Density and Volume Calculations

• Density (): , where is mass and is volume.

• Volume of a Sphere:

Example: To find the mass of a copper sphere, first calculate the volume using its radius, then multiply by the density.

Significant Figures in Calculations

• Addition/Subtraction: The result should have the same number of decimal places as the measurement with the fewest decimal places.

• Multiplication/Division: The result should have the same number of significant figures as the measurement with the fewest significant figures.

Example: (rounded to two decimal places).

Atoms, Isotopes, and the Periodic Table

Atomic Structure and Isotopes

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

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

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

Example: represents germanium (Ge), since atomic number 32 corresponds to Ge.

Ion Formation

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

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

Example: Removing 6 electrons from forms .

Isotopic Abundance Calculations

To calculate the mass or percentage of an isotope in a sample:

• Use the formula:

Example: For chlorine isotopes, use the given abundances and masses to find the mass of in 100 g of chlorine.

Classification of Elements

Metals, Nonmetals, and Metalloids

• Metals: Good conductors, malleable, ductile, shiny (e.g., Na, Ca).

• Nonmetals: Poor conductors, brittle, dull (e.g., N, Br).

• Metalloids: Properties intermediate between metals and nonmetals (e.g., Si).

Periodic Table Groups

• Alkali Metals: Group 1 (e.g., Na, K).

• Alkaline Earth Metals: Group 2 (e.g., Ba, Ca).

• Halogens: Group 17 (e.g., Cl, At).

• Noble Gases: Group 18 (e.g., Ne).

Main-Group vs. Transition Elements

• Main-Group Elements: Groups 1, 2, and 13–18.

• Transition Elements: Groups 3–12 (e.g., vanadium is in group 5B, a transition metal).

Visualizing Elements and Molecules

Atomic and molecular representations help visualize the structure of elements and compounds:

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

• Diatomic Molecular Element: Pairs of atoms bonded together (e.g., O2, N2).

States of Matter at Standard Conditions

• At standard temperature and pressure, most elements are solids, but some exist as liquids (e.g., Hg, Br2) or gases (e.g., N2, O2).

Electron Gain and Loss: Ions and Periodic Trends

• Metals tend to lose electrons to form cations.

• Nonmetals tend to gain electrons to form anions.

Example: Al and Pb are expected to lose electrons; N and O are expected to gain electrons.

Common Element Names and Symbols

Summary Table: Metals vs. Nonmetals

Summary Table: Group Names

Additional info: Some explanations and tables have been expanded for clarity and completeness, and standard definitions have been provided to ensure the notes are self-contained and suitable for exam preparation.