Atoms and Their Structure Notes PDF

Atoms and Their Structure What is an Atom? ​ Definition: The smallest unit of matter that retains the properties of an element. ​ Components: Atoms are made of three main particles: protons, neutrons, and electrons. Structure of an Atom ​ Nu...

Atoms and Their Structure What is an Atom? ​ Definition: The smallest unit of matter that retains the properties of an element. ​ Components: Atoms are made of three main particles: protons, neutrons, and electrons. Structure of an Atom ​ Nucleus: ​ The dense, central part of an atom. ​ Contains protons (positively charged) and neutrons (neutral/no charge). ​ Most of the atom’s mass is concentrated here. ​ Electron Cloud: ​ Surrounds the nucleus. ​ Contains electrons (negatively charged).  ​ Electrons move in regions of space called orbitals. Subatomic Particles Particle Charge Location Relative Mass Proton Positive (+) In the nucleus Heavy Neutron Neutral (0) In the nucleus Heavy Electron Negative Electron Very light (-) cloud Key Concepts ​ Ions: ​ Atoms that have gained or lost electrons, giving them a charge. ​ Cation: Positively charged ion (lost electrons). ​ Anion: Negatively charged ion (gained electrons). ​ Isotopes: ​ Atoms of the same element with different numbers of neutrons. ​ Example: Carbon-12 and Carbon-14. ​ Atomic Number: ​ The number of protons in an atom. ​ Determines the element. ​ Mass Number:  ​ The total number of protons and neutrons in an atom. Atoms vs. Elements, Compounds, and Mixtures ​ Element: ​ A pure substance made of only one type of atom (e.g., Oxygen, O₂). ​ Compound: ​ A substance made of two or more elements chemically bonded (e.g., H₂O). ​ Mixture: ​ A combination of two or more substances that are not chemically bonded (e.g., saltwater). Visual Aid: Comparing Key Terms Concept Example Key Feature Atom Carbon (C) Smallest unit of matter Element Oxygen (O₂) Made of one type of atom Compoun Water (H₂O) Chemically bonded elements d Mixture Air Physically combined substances The history of the atomic model is an excellent way to tie key principles of science to real-world examples. Here's how each principle can connect to the development of the atomic model: The natural world is understandable Scientists sought to understand the nature of matter, starting with Democritus's idea of "atomos" (indivisible particles) and evolving into more detailed models as understanding grew. This demonstrates the belief that the natural world can be comprehended through systematic inquiry. Science demands evidence - Each stage of the atomic model's development was supported by experimental evidence: Dalton’s atomic theory relied on chemical reaction observations. Thomson’s cathode ray tube experiments revealed the electron. Rutherford’s gold foil experiment provided evidence for a dense nucleus. Bohr’s model explained the quantized nature of electron orbits using spectroscopic data. Science is a blend of logic and imagination  Thomson, Rutherford, Bohr, and others used imagination to propose models (like the plum pudding and planetary models), yet these were logically based on evidence from experiments. Scientific knowledge is durable While models have been refined, the foundational ideas such as atoms being the building blocks of matter remain valid. Each new model builds on past insights rather than discarding them entirely. Scientific knowledge is subject to change The atomic model has evolved dramatically—from indivisible particles (Democritus) to electrons embedded in a positive sphere (Thomson), to a dense nucleus with orbiting electrons (Rutherford and Bohr), and now to quantum mechanics. This reflects the self-correcting nature of science. Scientists attempt to identify and avoid bias Scientists like Dalton and Rutherford conducted rigorous experiments and relied on repeatable observations rather than preconceived notions. This commitment helped refine models and correct earlier misconceptions. Science is a complex social activity The development of the atomic model was a collaborative effort over centuries. Ideas were shared, debated, and refined by scientists from different backgrounds and time periods, such as Thomson, Rutherford, Bohr, Schrödinger, and Heisenberg. Mixtures and Solutions What is a Mixture? A mixture is a combination of two or more substances where: ​ Each substance retains its original properties. ​ The substances can be physically separated. Mixtures can be categorized as: 1.​ Homogeneous Mixture: The components are evenly distributed, and you cannot see the individual parts (e.g., saltwater). 2.​ Heterogeneous Mixture: The components are not evenly distributed, and the individual parts are visible (e.g., a salad). What is a Solution? A solution is a special type of homogeneous mixture where one substance dissolves in another: ​ The solute is the substance that dissolves (e.g., salt in saltwater). ​ The solvent is the substance that does the dissolving (e.g., water in saltwater). Example: ​ In a saltwater solution: ​ Salt is the solute. ​ Water is the solvent. Saturation and Solubility:  ​ A solution becomes saturated when it cannot dissolve any more solute at a specific temperature. ​ Saturation Point - when no more solute can dissolve. ​ Unsaturated Solution: Can dissolve more solute. ​ Supersaturated Solution: Contains more dissolved solute than a saturated solution due to being heated and then cooled carefully. Using a Solubility Curve: A solubility curve is a graph that shows how much solute can dissolve in a solvent at different temperatures. ​ The x-axis typically represents temperature. ​ The y-axis represents the amount of solute (usually in grams) that can dissolve in a specific amount of solvent (usually 100 grams of water) ​ Solids usually become more soluble as temperature increases. ​ Gasses become more soluble as temperature decreases. ​ Solubility increases as pressure increases. Steps to Use a Solubility Curve: 1.​ Locate the temperature on the x-axis. 2.​ Find the corresponding point on the curve for your solute. 3.​ Determine the solubility by reading the value on the y-axis. 4.​ Compare your solution: ​ If the amount of solute is below the curve, the solution is unsaturated. ​ If the amount of solute is on the curve, the solution is saturated. ​ If the amount of solute is above the curve, the solution is supersaturated. Examples: 1.​ At 20°C, 36 grams of salt can dissolve in 100 grams of water. If you have 25 grams of salt, the solution is unsaturated. 2.​ At 60°C, if 275 grams of sugar dissolves in water and you try to add more sugar, the extra will remain undissolved, meaning the solution is saturated. Physical Properties in Science Physical properties are characteristics of a substance that can be observed or measured without changing the substance into something new. These properties help us identify and describe different materials. Key Physical Properties 1.​ Luster describes how a material reflects light. ​ Examples: ​ Metallic luster: Shiny like metals (e.g., gold or silver). ​ Non-metallic luster: Dull, glassy, shiny, brilliant... (e.g., wood or rubber). 2.​ Texture is how a material feels to the touch. ​ Examples: ​ Smooth (e.g., glass). ​ Rough (e.g., sandpaper). ​ Soft (e.g., cotton). 3.​ Malleability is the ability of a material to be hammered or rolled into thin sheets without breaking. ​ Examples: ​ High malleability: Aluminum, gold. ​ Low malleability: Glass, ceramics. 4.​ Electrical Conductivity measures how well a material allows electricity to pass through it. ​ Examples: ​ Good conductors: Copper, silver.  ​ Poor conductors (insulators): Plastic, rubber. 5.​ Density is the amount of mass in a given volume. ​ Formula: D = M/V (Density = mass / volume) ​ ​Units: grams per centimeter cubed (g/cm3) ​ Examples: ​ High density: Lead, gold. ​ Low density: Styrofoam, cork. 1.​ Melting Point is the temperature at which a solid changes into a liquid. ​ Examples: ​ High melting point: Iron (1538°C). ​ Low melting point: Ice (0°C). Why Are Physical Properties Important? Physical properties are used in: ​ Identifying unknown substances. ​ Selecting materials for specific purposes (e.g., building, electronics). ​ Comparing and classifying different substances.