JF

Chemistry: Matter, Properties, and Changes

What is Chemistry?

  • Definition: Chemistry is the study of matter and its properties, including what happens when matter interacts with other matter.

  • Importance: Chemistry is fundamental to everyday life and various job sectors.

    • Examples: Used in gardening (fertilizers), constitutes our DNA, is present in laundry and dish soap, impacts wildlife (e.g., acid rain making rain acidic, harming aquatic life and forests), and is crucial in the makeup and food nutrition industries, among many others.

Matter

  • Definition: Matter is anything that has mass and volume; anything that weighs something and takes up space.

  • Examples: A dog, food, a chair, humans, paper towel, water.

  • Types of Matter:

    • Elements:

      • Definition: The basic building blocks of everything; substances consisting of only one type of atom. They are what you find on the periodic table.

      • Examples: Oxygen, Nitrogen, Potassium, Sodium, Gold, Nickel, Copper, Helium.

    • Compounds:

      • Definition: Two or more elements that are chemically bonded together. They cannot be physically pulled apart.

      • Examples: H2O (water, made up of hydrogen and oxygen bonded together), CO2 (carbon dioxide), NaCl (sodium chloride, or table salt).

    • Mixtures:

      • Definition: Two or more elements or compounds that are physically mixed but not chemically bonded. Their components can often be separated.

      • Examples: Coffee (where coffee grounds and water mix but don't chemically combine), sugar water (sugar dissolves but does not chemically bond with water), Gatorade, salad (components are visibly separate).

Classification of Matter

  • Pure Substances:

    • Definition: Consist of only one type of particle.

    • Includes: Elements and Compounds.

    • Explanation for Compounds: A compound like water (H2O) is considered a pure substance because every single water particle is identical, consisting of two hydrogen atoms and one oxygen atom chemically bonded. In a glass of pure water, all particles are H2O, making it one type of particle.

  • Mixtures:

    • Definition: Consist of more than one type of particle.

    • Types of Mixtures:

      • Solutions (Homogeneous Mixtures):

        • Definition: A mixture that is mixed well and looks like one uniform substance. The components are not chemically combined.

        • Examples: Sugar water (looks like just water but contains both sugar and water particles), coffee, the air around us (looks like one thing but is a mixture of oxygen, carbon dioxide, nitrogen, and other gases), rainwater (looks like water but contains minerals), brass (a metal alloy made of different metals, but appears as one uniform metal).

      • Mechanical Mixtures (Heterogeneous Mixtures):

        • Definition: A mixture where the different parts are visibly distinguishable and do not mix uniformly. These are easier to identify as mixtures.

        • Examples: Salad (you can see the lettuce, cucumber, onion, etc.), toothpaste (if different colors are visible), pizza, sandwiches.

Properties and Changes of Matter

  • Physical Properties:

    • Definition: Observable characteristics of a substance, describing what you notice about it.

    • Categories:

      • Qualitative Properties: Descriptions without numbers (e.g., color, texture, smell).

      • Quantitative Properties: Descriptions that involve numbers or quantities (e.g., wind blowing at 5 kilometers per hour).

  • Physical Changes:

    • Definition: Changes that do not alter the chemical makeup of the materials involved. The identity of the substance remains the same, but its size, shape, or state may change.

    • Specifics: While the chemical makeup doesn't change, new physical properties might emerge (e.g., sweet taste of sugar water).

    • Examples:

      • Dissolving: Dissolving sugar into water changes the water's taste (a new physical property) but the sugar remains sugar and water remains water; they haven't chemically reacted or bonded. The sugar can be recovered by boiling off the water.

      • Changing State of Matter: Freezing water still results in H_2O, just in a solid state.

      • Changing Size or Shape: Ripping a sheet of paper in half still leaves you with paper; only its size has changed.

      • Other Examples: Breaking glass, mixing candies in a bowl, shredding paper, folding paper, melting ice, chopping wood, cutting hair, dry ice sublimation (changing state), boiling water, breaking eggs.

  • Chemical Properties:

    • Definition: Describes a substance's ability to react and form new substances. These properties are used to test for chemical changes.

    • Examples: Paper is flammable, iron rusts in the presence of oxygen, food rots.

  • Chemical Changes (Chemical Reactions):

    • Definition: Changes in substances that alter their chemical makeup, resulting in the formation of entirely new substances with new physical and chemical properties.

    • Examples:

      • Burning Paper: A blank white sheet of paper chemically changes into gray ash, which has a different chemical composition.

      • Rusting Iron: Iron chemically reacts with oxygen to form rust, a new substance.

      • Food Rotting/Ripening: A green banana becomes sweeter as it yellows because the chemical compounds within it change, producing more sugar. The actual chemical makeup of the banana is altered.

      • Other Examples: Cooking an egg (changes its chemical makeup), anything to do with baking or cooking, electroplating, creating batteries, a rotten banana, the reaction between vinaigrette and baking soda, fireworks, a chemical battery.

    • Five Signs of Chemical Changes (Evidence): Since we cannot see chemical makeup directly, these observable signs indicate a chemical change has occurred:

      • Bubbles forming (indicating gas formation).

      • Color change.

      • Odor change.

      • Solid forms (precipitate).

      • Energy changes (e.g., heat released or absorbed, light produced).