Chemical Properties of Matter: Sixth Grade Science
Chemical properties describe a substance's potential to undergo chemical transformations, react with other substances, and form entirely new products with distinct chemical identities.
The Nature of Chemical Properties
While physical properties can be measured without altering the chemical makeup of a substance, chemical properties can only be observed and measured when a substance undergoes a chemical change. A chemical property describes how the atomic bonds of a substance break, rearrange, or resist change when exposed to other elements, compounds, heat, or electricity. Once a chemical property is tested, the original substance is irrevocably transformed into new chemical compounds.
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| CORE CHEMICAL PROPERTIES OF MATTER |
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| Chemical Property | Scientific Definition and Chemical Behavior |
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| Flammability / | The ability of a substance to ignite, burn, and |
| Combustibility | sustain combustion in the presence of oxygen and heat.|
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| Reactivity with | The tendency of a metal to react with atmospheric O2 |
| Oxygen (Oxidation) | to form oxides (such as iron rusting or copper patina)|
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| Reactivity with | How vigorously a material reacts with acids to produce|
| Acids | hydrogen gas, salts, or fizzing effervescence. |
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| Reactivity with | The violent or mild reaction of elements (like sodium |
| Water | or potassium) when dropped into pure water. |
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| Chemical Toxicity | The degree to which a substance damages or poisons |
| | living tissue, enzymes, or cellular metabolism. |
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| Chemical Stability | The resistance of a substance to chemical breakdown |
| (Inertness) | or decomposition over time under normal conditions. |
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Flammability and Combustion
Flammability is the measure of how easily a substance catches fire when exposed to a spark or flame in an oxygen-rich environment. Wood, gasoline, alcohol, and methane gas possess high flammability. When gasoline burns inside an engine cylinder, hydrocarbons react vigorously with oxygen molecules, releasing radiant light and thermal energy while producing entirely new chemical substances: carbon dioxide gas and water vapor. In contrast, substances such as water, helium gas, and sand (silicon dioxide) have zero flammability; they are non-combustible and cannot burn.
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| THE CHEMISTRY OF COMBUSTION |
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| [ FUEL ] + [ OXYGEN ] + [ IGNITION SPARK ] |
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| v v v |
| (Hydrocarbon) (O2 Gas) (Activation Energy) |
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| CHEMICAL REACTION |
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| v |
| [ CARBON DIOXIDE (CO2) ] + [ WATER VAPOR (H2O) ] + [ HEAT & LIGHT ] |
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Oxidation: Rusting Versus Tarnishing
Oxidation is a chemical property describing how readily a substance loses electrons when reacting with oxygen:
- Rusting: Iron and steel react slowly with oxygen in the presence of moisture (water) to form hydrated iron(III) oxide, commonly known as rust (Fe2O3). Rust is a flaky, reddish-brown brittle compound that expands and flakes off, continually exposing fresh iron underneath to further destruction.
- Tarnishing: Silver reacts with trace sulfur compounds in the air to form a dark, thin coating of silver sulfide (Ag2S). Unlike rust, tarnish forms a protective surface barrier that slows further corrosion.
- Patina: Copper reacts over decades with atmospheric oxygen, carbon dioxide, and sulfur to form a beautiful greenish coating of basic copper carbonate, which protects monuments like the Statue of Liberty from corroding away.
Reactivity with Acids and the Carbonate Test
Reactivity with acids is an essential diagnostic chemical property used by geologists. When a drop of dilute hydrochloric acid (HCl) is placed onto the mineral calcite (calcium carbonate, CaCO3), a vigorous chemical reaction occurs immediately. The acid breaks the carbonate bonds, releasing fizzing bubbles of carbon dioxide gas (CO2) in a process called effervescence. Minerals such as quartz (SiO2) lack this chemical property and show zero reaction when acid is applied.
Chemical Inertness: The Noble Gases
Some substances are defined scientifically by their lack of chemical reactivity. The noble gases (helium, neon, argon, krypton, xenon, and radon) located in Group 18 of the periodic table have full outer valence electron shells. Because their electron configurations are completely stable, they do not gain, lose, or share electrons under standard conditions. They are chemically inert—they do not burn, do not rust, and do not react with acids or water. This chemical property makes helium ideal for blimps (unlike flammable hydrogen) and argon ideal for filling incandescent light bulbs to protect hot tungsten filaments.
Exercises and Solutions
Exercise 1: Contrasting Physical and Chemical Properties. Read the following descriptions of pure ethanol (grain alcohol): (1) It is a clear, colorless liquid at room temperature; (2) It has a boiling point of 78.4 degrees Celsius; (3) It has a density of 0.789 g/mL; (4) It ignites readily when exposed to an open spark; (5) It neutralizes certain strong oxidizing reagents to form acetic acid. Categorize each numbered statement as either a physical property or a chemical property, and justify your classification for statements (2) and (4).
Solution 1: Statements (1), (2), and (3) are physical properties; statements (4) and (5) are chemical properties. Statement (2) describes boiling point, which is a physical property because measuring it involves a phase transition from liquid to gas without changing the chemical identity of the ethanol molecules (both liquid and vapor are pure C2H5OH). Statement (4) describes flammability, which is a chemical property because testing ignition causes the ethanol to react with atmospheric oxygen, combusting into completely new substances (carbon dioxide and water vapor).
Exercise 2: Evaluating Protective Chemical Coatings. Architectural engineers designing a marine bridge can choose between structural steel beams and steel coated with a sacrificial zinc layer (galvanized steel). In a coastal environment with salty, humid air, plain steel oxidizes rapidly into rust within months. Explain the chemical property of zinc that prevents the bridge from collapsing and describe what happens at the atomic level during sacrificial protection.
Solution 2: Zinc possesses a higher chemical reactivity with oxygen and corrosive electrolytes than iron. When steel is galvanized, the zinc outer layer acts as a sacrificial anode. The zinc oxidizes preferentially before the underlying iron can react, forming a tough, impermeable barrier of zinc carbonate that shields the metal underneath. Even if the coating is scratched and the bare steel is exposed to salty air, the remaining zinc continues to donate electrons to the iron, chemically preventing the iron atoms from oxidizing into brittle rust and preserving the structural strength of the bridge.