1.3 Physical and Chemical Properties

1.3 Physical and Chemical Properties

• Learning objectives

  • Identify properties of and changes in matter as physical or chemical

  • Identify properties of matter as extensive or intensive

• Key concepts

  • Properties: the characteristics that distinguish one substance from another.

  • Physical property: a property of matter that is not associated with a change in its chemical composition.

  • Physical properties include: density, color, hardness, melting point, boiling point, and electrical conductivity.

  • Some physical properties (e.g., density and color) may be observed without changing the physical state of the matter. Other physical properties (e.g., the melting temperature of iron or the freezing temperature of water) are observed only as matter undergoes a physical change.

  • Physical change: a change in the state or properties of matter without any accompanying change in the chemical identities of the substances contained in the matter.

  • Examples of physical changes: wax melts; sugar dissolves in coffee; steam condenses into liquid water; magnetizing and demagnetizing metals (e.g., security tags); grinding solids into powders.

  • In each physical-change example, there is a change in the physical state, form, or properties of the substance, but no change in chemical composition.

  • Figures referenced: Figure 1.18 (illustrations of physical changes: wax melting and steam condensation).

• Chemical properties

  • Chemical property: the change of one type of matter into another type (or the inability to change).

  • Examples of chemical properties: flammability, toxicity, acidity, and various types of reactivity.

  • Iron rusts in the presence of oxygen and water (rust formation is a chemical property/behavior). Chromium does not oxidize under the same conditions (oxidation resistance).

  • Nitroglycerin is very dangerous because it explodes easily; neon is very unreactive.

  • Figure 1.19 contrasts iron rusting with chromium not oxidizing.

• Chemical changes

  • A chemical change always produces one or more types of matter that differ from the matter present before the change.

  • Examples:

  • Rust formation: rust is a different kind of matter from iron, oxygen, and water that produced it.

  • Explosion of nitroglycerin: the gases produced are very different from the original substance.

  • Copper reacting with nitric acid (lab example).

  • All forms of combustion (burning).

  • Cooking, digestion, or rotting of foods.

  • Figure 1.20 shows several chemical changes: copper with nitric acid, combustion of a match, cooking red meat, and banana browning.

• Observations and classifications of properties

  • Extensive properties: depend on the amount of matter present.

  • Examples: mass and volume.

  • A larger amount of matter has a larger extensive property value (e.g., a gallon of milk has more mass than a cup of milk).

  • Formal statement: an extensive property P_ext ∝ amount of matter (e.g., mass m or volume V).

  • Intensive properties: do not depend on the amount of matter present.

  • Example: temperature.

  • When two samples at the same temperature are combined, the temperature remains the same (T_combined = T each).

  • Related concept: heat vs temperature. A drop of hot cooking oil vs a pot of hot oil can have the same temperature but very different amounts of heat.

    • Heat (distinct but related to temperature) is an extensive property: the pot contains more heat than the drop.

    • Conceptual relation: if we denote heat content by H, then a larger sample typically has a larger H (i.e., H ∝ amount).

  • Practical distinction helps predict behavior: e.g., a small sample and a large sample at the same temperature may behave differently in terms of heat transfer and energy content.

• Chemistry in Everyday Life: Hazard Diamond (NFPA 704)

  • The NFPA 704 Hazard Identification System provides quick safety information about hazards.

  • The hazard diamond has four colored sections within a larger diamond:

  • Top (red) = Fire hazard (flammability/flash point)

  • Left (blue) = Health hazard

  • Right (yellow) = Reactivity hazard

  • Bottom (white) = Special hazards (e.g., oxidizer, corrosive, water-reactive, biohazard, radioactive)

  • Each hazard is rated on a scale from 0 to 4 (0 = no hazard; 4 = extremely hazardous).

  • Flash point scales (top red) in the example:

  • 4: Below $73^{\circ}\mathrm{F}$

  • 3: Below $100^{\circ}\mathrm{F}$

  • 2: Above $100^{\circ}\mathrm{F}$ not exceeding $200^{\circ}\mathrm{F}$

  • 1: Above $200^{\circ}\mathrm{F}$

  • 0: Will not burn

  • Health hazard (blue) and reactivity hazard (yellow) scales run 0–4; higher numbers indicate greater hazard.

  • White section highlights special hazards such as oxidizers, corrosives, acids, bases, radioactive materials, etc.

  • The NFPA 704 system was developed to provide safety information about substances and assist in risk assessment and safe handling.

• Metals, nonmetals, and metalloids; periodic table organization

  • Elements can be grouped by similar properties into three broad classes:

  • Metals: good conductors of heat and electricity

  • Nonmetals: poor conductors

  • Metalloids: intermediate conductivities

  • The periodic table places elements with similar properties near each other, enabling predictions of behavior and reactivity.

  • Figure 1.22 details the periodic table with:

  • Background color coding indicating metal, metalloid, or nonmetal

  • Element symbol color indicating the state of matter (solid, liquid, or gas)

• The Periodic Table excerpt (illustrative data from Figure 1.22)

  • Example entries and basic data (atomic number, approximate atomic mass):

  • Hydrogen (H): atomic number $1$; atomic mass $1.008$

  • Lithium (Li): atomic number $3$; atomic mass $6.94$

  • Beryllium (Be): atomic number $4$; atomic mass $9.012$

  • Sodium (Na): atomic number $11$; atomic mass $22.99$

  • Magnesium (Mg): atomic number $12$; atomic mass $24.31$

  • Aluminum (Al): atomic number $13$; atomic mass $26.98$

  • Silicon (Si): atomic number $14$; atomic mass $28.09$

  • Phosphorus (P): atomic number $15$; atomic mass $30.97$

  • Sulfur (S): atomic number $16$; atomic mass $32.06$

  • Chlorine (Cl): atomic number $17$; atomic mass $35.45$

  • Argon (Ar): atomic number $18$; atomic mass $39.95$

  • The excerpt also shows later elements and a broader arrangement by periods and groups, with a color-coded scheme to indicate metals, metalloids, nonmetals and states of matter.

• Connections and implications

  • Distinguishing physical vs chemical properties helps predict how substances will behave in reactions.

  • Distinguishing extensive vs intensive properties informs how properties scale with amount.

  • NFPA hazard diamond supports workplace safety and risk assessment.

  • Understanding metals, nonmetals, and metalloids, as well as periodic trends, aids in predicting element behavior and reactivity.

• Practical takeaways and cautions

  • Safety first: handle reactive substances (e.g., nitroglycerin) with appropriate precautions.

  • Be mindful of the difference between temperature and heat when interpreting data or making qualitative judgments about energy content.

  • Common examples of physical vs chemical changes to reinforce understanding (e.g., wax melting vs iron rusting).

• Summary of key distinctions

  • Physical properties do not alter chemical identity; physical changes do not form new substances.

  • Chemical properties describe a substance’s potential to undergo chemical change.

  • Chemical changes produce new substances; physical changes do not.