Science Reviewer PDF

Science Reviewer Particulate Nature of Matter Matter is made of tiny particles called atoms. There is space between the particles. Particles are always moving. Forces act between the particles. Atoms can be broken into smaller particles (subatomic particles). States of Matter Soli...

Science Reviewer Particulate Nature of Matter Matter is made of tiny particles called atoms. There is space between the particles. Particles are always moving. Forces act between the particles. Atoms can be broken into smaller particles (subatomic particles). States of Matter Solid Has a definite shape and volume. Particles are packed tightly and vibrate in place. Hard to compress (low compressibility). High density. Does not flow. Liquid Takes the shape of its container (no fixed shape). Has a definite volume. Particles are close but can slide past each other. Low compressibility. Flows easily. Gas Has no definite shape or volume. Particles are far apart and move freely. Easy to compress (high compressibility). Low density. Flows easily. Phase Changes Definition: A phase change is a change from one state of matter (solid, liquid, gas) to another. These are physical changes because  they: Only affect physical appearance, not chemical make-up. Are reversible. What Happens During a Phase Change Heat energy is absorbed or released: Heat absorbed: Molecules speed up and move farther apart. Heat released: Molecules slow down and move closer together. Types of Phase Changes Melting: Solid to liquid (heat absorbed, molecules speed up and move apart). Freezing: Liquid to solid (heat released, molecules slow down and move closer). Vaporization (Boiling): Liquid to gas at boiling point (heat absorbed, molecules move faster and spread out). Evaporation: Liquid to gas at any temperature (heat absorbed, molecules move faster and spread out). Condensation: Gas to liquid (heat released, molecules slow down and move closer). Sublimation: Solid to gas (heat absorbed, molecules move faster and spread out). Deposition: Gas to solid (heat released, molecules slow down and move closer). Summary Table of Phase Changes  Phase Change Process Heat Energy Melting Solid to liquid Absorb Freezing Liquid to solid Release Evaporation Liquid to gas Absorb Condensation Gas to liquid Release Sublimation Solid to gas Absorb Deposition Gas to solid Release Mixtures, Elements, and Compounds Classification of Matter All matter can be classified as mixtures, elements, or compounds. Why not classify by phases? Substances can exist in more than one phase (e.g., H₂O). Why not classify by physical characteristics? Grouping by color (e.g., gold, sunflowers, and the sun) is not useful. How Scientists Classify Matter 1. Is the matter uniform throughout? 2. Can it be separated by physical means? 3. Can it be separated by chemical means? Mixtures Two or more substances not chemically combined and can be separated physically. Substances retain individual properties. Heterogeneous Mixtures Not uniform throughout. Least mixed; particles are large and visible. Examples: Sand and pebbles, oil and water, granite. Homogeneous Mixtures Uniform throughout and well-mixed. Particles are small and not easily recognizable. Examples: Milk, toothpaste, mayonnaise (colloids). Solutions A homogeneous mixture where one substance dissolves in another. Solute: Substance being dissolved. Solvent: Substance doing the dissolving. Example: Ocean water (salt in water). Types of Solutions Solute Solvent Example Gas Gas Air (oxygen in nitrogen) Gas Liquid Soda water (CO₂ in water) Solid Liquid Ocean water (salt in water) Solid Solid Gold jewelry (copper in gold) Alloys  Mixtures of metals. Examples: Brass (copper + zinc), stainless steel (iron + chromium). Pure Substances 1. Elements Simplest pure substance, cannot be broken down by physical or chemical means. Made of atoms, which are the basic building blocks of matter. Examples: Oxygen (O), Gold (Au). 2. Compounds Pure substances made from two or more elements chemically combined. Can be broken down chemically. Example: Water (H₂O → hydrogen + oxygen). Atomic Theory and Models Democritus: Atomos Proposed that matter is composed of small, indivisible particles called atoms. Atoms were: Small, hard particles made of the same material but different in shape and size. Infinite in number, always moving, and capable of joining together. Dalton’s Atomic Model John Dalton revived the atomic theory, stating: All elements are composed of atoms (indivisible and indestructible). Atoms of the same element are identical. Atoms of different elements differ.  Compounds are formed by the combination of atoms of two or more elements. Thomson’s Plum Pudding Model J.J. Thomson discovered electrons and proposed: Atoms are made of a positively charged substance with negatively charged electrons embedded, like raisins in pudding. Rutherford’s Nuclear Model Ernest Rutherford’s gold foil experiment: Atoms consist of a dense, positively charged nucleus. Negatively charged electrons orbit the nucleus. Bohr’s Planetary Model Niels Bohr refined the model: Electrons move in specific orbits (energy levels) around the nucleus, like planets around the sun. Wave Model (Modern Atomic Theory) Electrons do not follow fixed paths but exist in electron clouds around the nucleus. The location of electrons depends on their energy. Subatomic Particles  Particle Discoverer Charge Mass (g) Location Electron J.J. -1 ~9.11×10⁻³¹ Outside Thomson nucleus (1897) Proton Ernest +1 ~1.67×10⁻²⁴ In nucleus Rutherford Neutron James 0 ~1.67×10⁻²⁴ In nucleus Chadwick (1932) Chemical Change Definition: A chemical change forms a new substance with unique properties. The original substance is no longer recognizable. Examples of Chemical Changes Rusting of iron. Combustion (burning) of wood. Cooking an egg. Baking a cake. Explosion of fireworks. Milk going sour. Evidences of Chemical Change Formation of Precipitates: A solid forms when two liquids are mixed. Energy Release or Absorption: Often accompanied by light, heat, or sound.