1.3 Physical and Chemical Properties

The characteristics that distinguish one substance from another are called properties.
A physical property is a characteristic of matter that is not associated with a change in its chemical composition.
Examples of physical properties: $\text{density}, \ \text{color}, \ \text{hardness}, \ tm, \ tb, \ \text{electrical conductivity}$ .
Some physical properties (like density and color) can be observed without a change in physical state; others require a physical change (e.g., melting iron, freezing water).

A physical change is a change in the state or properties of matter without any accompanying change in the chemical identities of the substances.
Examples: wax melting, sugar dissolving in coffee, steam condensing to liquid water.
Other physical changes: magnetizing/demagnetizing metals; grinding solids into powders.

A chemical property is the ability to change from one type of matter into another (or the inability to change).
Examples of chemical properties: flammability, toxicity, acidity, and various types of reactivity.
Iron rusts (with oxygen and water) — rust is a different kind of matter from the original iron, oxygen, and water. Chromium does not oxidize.
Nitroglycerin explodes easily; neon is very unreactive.
A chemical change always produces matter that differs from the matter present before the change (e.g., rust formation, gas production in explosions).
Additional examples of chemical changes: copper reacting with nitric acid; combustion; cooking, digestion, or rotting of food; browning of a banana.
Example reactions: $\text{Cu} + 2\,\text{HNO}3 \rightarrow \text{Cu(NO}3)2 + \text{NO}2\uparrow$ ; burning cellulose with oxygen → $\text{CO}2 + \text{H}2\text{O}$ ; cooking red meat involves chemical changes (e.g., iron oxidation in myoglobin).

An extensive property depends on the amount of matter present (e.g., mass, volume).
Example: a gallon of milk has more mass than a cup of milk.
An intensive property does not depend on the amount of matter (e.g., temperature).
Temperature consistency example: if a gallon and a cup of milk are both at 20 °C, mixing them keeps the temperature at 20 °C.
Distinguish heat vs temperature: a small drop of hot oil on the skin causes brief discomfort, a pot of hot oil causes severe burns; both at the same temperature, but the pot contains more heat (an extensive property).
Notation: state variables for phases are often represented as $s,\ l,\ g$ for solid, liquid, and gas.

The NFPA 704 hazard identification system provides safety information about substances.
The diamond has four colored sections: red (flammability), blue (health), yellow (reactivity), white (special hazards).
Scale for each section ranges from 0 to 4, where 0 = no hazard and 4 = extremely hazardous.
Special hazards in the white section may indicate oxidizers, corrosive, radioactive, etc.

Elements can be grouped by similar properties in the periodic table.
Some elements conduct heat and electricity well; others do not.
Elements are broadly classified as metals (good conductors), nonmetals (poor conductors), and metalloids (intermediate conductivities).
The periodic table places similar-property elements near each other.

The periodic table shows grouping by similar properties; elements in the same column (group) tend to have similar chemical behavior.
Visual cues: background color indicates metal/metalloid/nonmetal; symbol color indicates state at a given condition (solid, liquid, or gas).
You will learn more about the periodic table as you study chemistry.