9th Grade Midterms - Chemistry Study Guide PDF
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This document is a study guide for chemistry topics, suitable for 9th grade. It covers basic concepts like matter, properties, safety, and measurement. It also touches on topics like scientific notation and the scientific method.
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Simple Study Guide for Chemistry Topics - ttps://quizlet.com/996553997/comprehensive-study-guide-for-chemistry-topics-fl h ash-cards/?i=6cggl7&x=1jqt Matter D efinition: Anything that has mass and occupies space. States of Matter: Solid, liquid, gas, and plasma....
Simple Study Guide for Chemistry Topics - ttps://quizlet.com/996553997/comprehensive-study-guide-for-chemistry-topics-fl h ash-cards/?i=6cggl7&x=1jqt Matter D efinition: Anything that has mass and occupies space. States of Matter: Solid, liquid, gas, and plasma. Properties: ○ Physical: Characteristics observed without changing composition (e.g., color, melting point). ○ Chemical: Characteristics observed when matter undergoes a chemical change (e.g., flammability). Safety A lways wear appropriate lab gear (goggles, gloves, lab coat). Know the location and proper use of safety equipment (fire extinguisher, eyewash station). Follow instructions precisely and handle chemicals with care. Never eat, drink, or taste substances in the lab. Measurement U se standard units from the International System of Units (SI): meters (m), kilograms (kg), seconds (s), etc. Precision: How close measurements are to one another. Accuracy: How close measurements are to the true value. Scientific Notation U sed to express very large or small numbers. Format: where. ○ Example: 0.00045 =. Significant Figures Rules: ○ Non-zero digits are significant. ○ Zeros between non-zero digits are significant. ○ Leading zeros are not significant. ○ Trailing zeros are significant if there’s a decimal point. When performing calculations: ○ Multiplication/Division: Result has the same number of sig. figs. as the value with the least sig. figs. ○ Addition/Subtraction: Result has the same decimal places as the value with the least decimal places. Unit Conversion U se dimensional analysis. Conversion factors express equivalence between units (e.g., 1 inch = 2.54 cm). Set up conversions so units cancel out. Lab Techniques C ommon Equipment: Beakers, test tubes, Bunsen burners, pipettes. Measuring Liquids: Use a graduated cylinder at eye level; read the meniscus. Handling Solids: Use a spatula or scoop. Chemical vs. Physical Change P hysical Change: Change in form, not composition (e.g., melting ice). Chemical Change: Formation of new substances (e.g., rusting iron). Atom B asic unit of matter. Structure: ○ Nucleus: Protons (+) and neutrons (neutral). ○ Electrons (-) orbit around the nucleus. Isotope Atoms of the same element with different numbers of neutrons. Example: Carbon-12 vs. Carbon-14. Electron N egatively charged subatomic particle. Found in energy levels or orbitals around the nucleus. Determines chemical properties and bonding. Electromagnetic Spectrum (EMS)[colors for daniel] R ange of all types of electromagnetic radiation. Includes (in order of increasing wavelength): Gamma rays, X-rays, UV, visible light, infrared, microwaves, radio waves. Scientific Method . 1 sk a question. A 2. Do background research. 3. Form a hypothesis. 4. Conduct experiments. 5. Analyze data. 6. Draw conclusions. 7. Share results. Thermal Energy E nergy related to temperature; the total kinetic energy of particles in a substance. Transfer: Conduction, convection, radiation. Light Energy A form of electromagnetic radiation. Travels in waves and behaves as particles (photons). Visible spectrum: ROYGBIV (red, orange, yellow, green, blue, indigo, violet). Half-Life T ime required for half of a radioactive substance to decay. Example: Carbon-14 has a half-life of 5,730 years. Formula: Where is remaining amount, is initial amount, is time elapsed, is half-life. Density Formula: Units: g/cm³ or kg/m³. Intensive property (does not depend on amount). Radioactive Decay P rocess where unstable nuclei emit radiation to become stable. Types: ○ Alpha (α): Helium nucleus emitted. ○ Beta (β): Electron or positron emitted. ○ Gamma (γ): High-energy photon emitted. Electron Configuration D istribution of electrons in an atom’s orbitals. Rules: 1. Aufbau Principle: Fill lowest energy orbitals first. 2. Pauli Exclusion Principle: Maximum of two electrons per orbital, opposite spins. 3. Hund's Rule: Fill degenerate orbitals singly before pairing. Example: Oxygen (8 electrons) = 1s² 2s² 2p⁴. Periodic Table rganized by increasing atomic number. O Groups/Families: Vertical columns (similar properties). Periods: Horizontal rows. Key Features: ○ Metals, Nonmetals, Metalloids. ○ Trends: Atomic size, ionization energy, electronegativity. Extensive study guide: Study Guide for Chemistry Topics Matter D efinition: Anything that has mass and occupies space. States of Matter: ○ Solid: Definite shape and volume; particles tightly packed. ○ Liquid: Definite volume but no fixed shape; particles slide past each other. ○ Gas: No fixed shape or volume; particles move freely. ○ Plasma: Ionized gas with free electrons and positive ions. Properties: ○ P hysical Properties: Characteristics observed without altering the substance’s identity (e.g., color, density, melting point, boiling point, solubility). ○ Chemical Properties: Characteristics that describe how a substance reacts to form new substances (e.g., combustibility, reactivity with acids). Classification: ○ Elements: Pure substances made of one type of atom. ○ Compounds: Substances composed of two or more elements chemically combined. ○ Mixtures: Physical combinations of substances that can be separated by physical means (homogeneous or heterogeneous). Safety Lab Safety Rules: ○ Always wear protective gear: goggles, gloves, and lab coats. ○ Avoid loose clothing and tie back long hair. ○ Never work alone in the lab. Emergency Procedures: ○ Know the locations of the fire extinguisher, eyewash station, and safety shower. ○ Report all accidents or spills immediately to the instructor. Chemical Handling: ○ Label all containers and handle with care. ○ Never mix chemicals unless instructed. ○ Dispose of chemicals as directed by your instructor. Measurement SI Units: ○ Length: meter (m) ○ Mass: kilogram (kg) ○ Time: second (s) ○ Temperature: kelvin (K) ○ Amount of substance: mole (mol) Tools and Techniques: ○ Use a balance for mass. ○ Measure liquids with a graduated cylinder (read the meniscus). ○ Use a thermometer for temperature. Uncertainty in Measurement: ○ Use proper significant figures to express precision. ○ Estimate one decimal place beyond the smallest marking on a measuring tool. Scientific Notation D efinition: A method to write very large or very small numbers in the form , where . ○ Example: ,. Operations: ○ Multiplication: Multiply coefficients, add exponents. ○ Division: Divide coefficients, subtract exponents. ○ Adding: Make sure exponents are the same, add like normal ○ Subtracting: Make sure exponents are the same, subtract like normal Significant Figures P urpose: Reflect the precision of a measurement. Counting Rules: ○ All non-zero digits are significant. ○ Zeros between non-zero digits are significant. ○ Leading zeros (zeros before non-zero digits) are not significant. ○ Trailing zeros are significant if the number contains a decimal point. Calculations: ○ Multiplication/Division: Use the least number of sig. figs. from the input values. ○ Addition/Subtraction: Match the least precise decimal place. Unit Conversion Dimensional Analysis: ○ Write the given quantity. ○ Multiply by conversion factors so the units cancel out. ○ Example: Convert 10 inches to centimeters: Common Conversions: ○ Length: 1 inch = 2.54 cm ○ Mass: 1 kg = 1000 g ○ Volume: 1 L = 1000 mL Lab Techniques Measuring Liquids: ○ Always read at eye level and at the meniscus (the bottom of the curve). ○ Use pipettes for precise volume transfers. Separating Mixtures: ○ Filtration: Separates solids from liquids. ○ Distillation: Separates substances based on boiling points. Heating Substances: U ○ se a Bunsen burner safely with a heat-resistant mat. ○ Monitor temperature with a thermometer. Chemical vs. Physical Change Physical Changes: ○ Affect the form but not the chemical composition (e.g., melting, freezing, dissolving). Chemical Changes: ○ Result in the formation of new substances (e.g., burning wood, rusting iron). ○ Indicators: Color change, gas formation, precipitate formation, heat/light emission. Atom Structure: ○ Nucleus: Protons (positive) and neutrons (neutral). ○ Electron Cloud: Electrons (negative) in orbitals. Atomic Number: Number of protons; determines element identity. Mass Number: Sum of protons and neutrons. Ions: Atoms with a charge due to loss/gain of electrons. Isotope D efinition: Variants of an element with the same number of protons but different numbers of neutrons causing the weight to change. Applications: ○ Carbon dating (Carbon-14). ○ Medical imaging (e.g., Technetium-99m). Electron Properties: ○ Negatively charged. ○ Mass is approximately 1/1836 of a proton. Behavior: ○ Occupy specific orbitals (s, p, d, f). ○ Energy levels are quantized. Electromagnetic Spectrum (EMS) Order of Waves: ○ Gamma rays (shortest wavelength, highest energy). X-rays, UV, visible light, infrared, microwaves, radio waves. ○ Visible Light: ○ Range: 400 nm (violet) to 700 nm (red). ○ Applications: Photosynthesis, vision. Scientific Method . 1 Identify a problem or question. 2. Research existing knowledge. 3. Form a testable hypothesis. 4. Conduct experiments (controlled variables). 5. Record and analyze data. 6. Draw conclusions; accept/reject hypothesis. 7. Share findings with the scientific community. Thermal Energy D efinition: The total kinetic energy of particles in a substance. Heat Transfer: ○ Conduction: Direct contact. ○ Convection: Movement of fluids. ○ Radiation: Transfer through electromagnetic waves. Light Energy Nature: ○ Behaves as both particles (photons) and waves. ○ Travels at a speed of in a vacuum. Applications: ○ Photosynthesis, fiber optics, lasers. Half-Life D efinition: Time required for half the nuclei in a sample to decay. Equation: ○ : Remaining quantity. ○ : Initial quantity. ○ : Time elapsed. ○ : Half-life. Examples: ○ Uranium-238 (4.5 billion years). ○ Iodine-131 (8 days). Density Formula: Importance: ○ Determines buoyancy. ○ Identifies substances. Units: ○ g/cm³, kg/m³. Example Calculation: ○ A block of wood has a mass of 200 g and a volume of 250 cm³: Radioactive Decay Types: ○ Alpha Decay: Emits a helium nucleus (α-particle). ○ Beta Decay: Converts a neutron into a proton (or vice versa), emitting an electron or positron. ○ Gamma Decay: Releases excess energy as high-energy photons. ○ Positron emission (0/1 e): A type of radioactive decay where an unstable isotope emits a positron, the antimatter equivalent of an electron. Applications: ○ Nuclear power, cancer treatment, radiometric dating. Electron Configuration Principles: ○ Aufbau Principle: Fill orbitals in order of increasing energy. ○ Pauli Exclusion Principle: No two electrons in an atom can have the same set of quantum numbers. ○ Hund’s Rule: Electrons occupy degenerate orbitals singly before pairing. Notation: ○ Example: Chlorine (17 electrons) = 1s² 2s² 2p⁶ 3s² 3p⁵. ○ S Orbital - Groups 1 and 2; Sphere Shaped ○ P Orbital - Groups 13-18; Dumbbell Shape ○ D Orbital - Transition Metals; Doule Dumbbell ○ F Orbital - Inner transition metals Periodic Table Structure: ○ G roups/Families: Columns; elements have similar valence electron configurations. ○ Periods: Rows; elements have the same number of electron shells. Trends: ○ Atomic Radius: Decreases across a period, increases down a group. ○ Ionization Energy: Increases across a period, decreases down a group. ○ Electronegativity: Increases across a period, decreases down a group. Key Regions: ○ Metals: Good conductors, malleable, ductile. ○ Nonmetals: Poor conductors, brittle. ○ Metalloids: Properties of both metals and nonmetals. Melting Points Factors: ○ Atomic Radius: Smaller atoms have a high melting point; therefore the smaller the atomic radius the larger the melting point ○ Bonds: Stronger bonds result in a higher melting point (Ex. Ionic > Covalent > Hydrogen Bonds etc.) Trends: ○ Metals generally have a higher melting point due to larger atomic radius ○ Higher melting points typically are the inverse of atomic radius trends 1. (Formation of Ions) Ions are atoms or groups of atoms that carry an electrical charge. Ions are formed when atoms gain or lose electrons to achieve a stable electronic configuration (often a full outer shell, like the noble gases). Types of Ions: Cations: Positively charged ions. ○ Formed when an atom loses electrons. ○ Common with metals, as they typically lose electrons to become stable. ○ Example: Sodium (Na) loses one electron to form Na+Na+. Anions: Negatively charged ions. ○ Formed when an atom gains electrons. ○ Common with non-metals, as they tend to gain electrons to fill their valence shell. ○ Example: Chlorine (Cl) gains one electron to form Cl−Cl−. Why Do Atoms Form Ions? toms form ions to become more stable by reaching the electronic configuration of the A nearest noble gas. This is guided by the octet rule, which states that atoms are most stable when they have 8 electrons in their outermost shell (or 2 for very small atoms like hydrogen and helium). Examples: M agnesium (MgMg): Loses 2 electrons to form Mg2+Mg2+. Oxygen (OO): Gains 2 electrons to form O2−O2−. 2. Bohr Models he Bohr Model is a simple atomic model proposed by Niels Bohr in 1913 to describe the T structure of the atom. It builds on earlier models by introducing quantized energy levels. Key Principles of the Bohr Model: 1. E lectrons Orbit the Nucleus: Electrons revolve around the nucleus in fixed, circular paths called energy levels or shells. 2. Quantized Energy Levels: Each shell corresponds to a specific energy level (n=1,2,3,n=1,2,3, etc.). Electrons can only exist in these levels, not in between. 3. Electron Transitions: ○ When an electron absorbs energy, it jumps to a higher energy level (excitation). ○ When it releases energy, it falls back to a lower energy level, emitting light (in the form of a photon). 4. Maximum Electrons per Shell: ○ The formula for the maximum number of electrons in a shell is 2n22n2, where nn is the shell number. n=1n=1: 2 electrons n=2n=2: 8 electrons n=3n=3: 18 electrons Example: Bohr Model of Sodium (Na): A tomic number = 11 (so it has 11 electrons). Distribution: ○ 1st shell (n=1n=1): 2 electrons ○ 2nd shell (n=2n=2): 8 electrons ○ 3rd shell (n=3n=3): 1 electron hile the Bohr Model is easy to visualize, it is limited. Later models (like the quantum W mechanical model) explain atomic structure more accurately. 3. Everything About Light ight is a form of electromagnetic radiation and can behave both as a wave and a L particle. Let’s explore its properties, nature, and how it interacts with matter. Properties of Light: 1. Speed of Light: ○ In a vacuum, light travels at c=3.00×108 m/sc=3.00×108m/s. 2. Wavelength (λλ): ○ Distance between two consecutive peaks or troughs of a wave. ○ Measured in meters (or nanometers for visible light). 3. Frequency (ff): ○ Number of wave cycles that pass a point per second. ○ Measured in hertz (HzHz). 4. Energy (EE): ○ The energy of light is directly proportional to its frequency and inversely proportional to its wavelength. ○ E=hfE=hf, where h=6.63×10−34 Jsh=6.63×10−34Js (Planck’s constant). Wave-Particle Duality: W ave Nature: Light behaves like a wave, showing properties like diffraction and interference. Particle Nature: Light is made of discrete packets of energy called photons. This is evident in phenomena like the photoelectric effect, where light knocks electrons off a metal surface. Electromagnetic Spectrum: ight is part of a spectrum of electromagnetic waves, arranged by wavelength and L frequency: amma Rays: Shortest wavelength, highest energy. G X-Rays Ultraviolet (UV) Visible Light: ○ Wavelength: ~400–700 nm. ○ Colors range from violet (shortest wavelength) to red (longest wavelength). Infrared (IR) Microwaves Radio Waves: Longest wavelength, lowest energy. Interactions of Light: . 1 eflection: Light bounces off a surface. R 2. Refraction: Light bends as it passes through different media. 3. Diffraction: Light spreads out when passing through small openings. 4. Absorption: Matter absorbs light, converting it into other forms of energy. Key Phenomena: 1. Photoelectric Effect: ○ Demonstrates light’s particle nature. ○ Light of a certain frequency ejects electrons from a metal surface. 2. Spectroscopy: ○ When atoms absorb or emit light, they produce unique spectral lines. ○ Used to identify elements and study their properties. Equations: 1. Weighted Average he weighted average is used when different values contribute unequally to the overall T average. Formula: Weighted Average=∑(wi⋅xi)∑wiWeighted Average=∑wi∑(wi⋅xi) w iwi: The weight or importance of each value. xixi: The value associated with each weight. ∑∑: Summation symbol, meaning "add up all the terms." Example: If a student has grades in two exams where the first exam is worth 40% (w1=0.4w1=0.4) and the second exam is worth 60% (w2=0.6w2=0.6): F irst exam grade: x1=85x1=85. Second exam grade: x2=90x2=90. eighted Average=(0.4⋅85)+(0.6⋅90)0.4+0.6=88Weighted W Average=0.4+0.6(0.4⋅85)+(0.6⋅90)=88 2. Percentage Average he percentage average is used to find the average percentage when you have multiple T percentages of different categories. It's like the weighted average, where the weights are based on the size of each category. Formula: ercentage Average=∑(Percentage⋅Weight)∑WeightsPercentage P Average=∑Weights∑(Percentage⋅Weight) F or cases where all percentages are equally weighted:Percentage Average=∑PercentagesNumber of ItemsPercentage Average=Number of Items∑Percentages Example: If a student scores: 8 0% in a test worth 50 points. 90% in a test worth 100 points. The weighted average percentage is: ercentage Average=(80⋅50)+(90⋅100)50+100=86.67%Percentage P Average=50+100(80⋅50)+(90⋅100)=86.67% 3. Half-Life The half-life is the time required for half the quantity of a substance to decay or reduce. Formula: N(t)=N0⋅(12)tTN(t)=N0⋅(21)Tt (t)N(t): The remaining quantity of the substance after time tt. N N0N0: The initial quantity of the substance. TT: Half-life of the substance. tt: Time elapsed. You can also solve for the half-life TT or tt based on the situation: T=tlog2(N0N(t))T=log2(N(t)N0)t Example: If a radioactive material has a half-life of 5 years, and you start with 100 grams, how much remains after 10 years? N(10)=100⋅(12)105=100⋅(12)2=25 gramsN(10)=100⋅(21)510=100⋅(21)2=25grams 4. Decay (Exponential Decay) The exponential decay formula models how quantities decrease over time. Formula: N(t)=N0⋅e−λtN(t)=N0⋅e−λt (t)N(t): The remaining quantity after time tt. N N0N0: The initial quantity of the substance. λλ: The decay constant (λ=ln(2)Tλ=Tln(2), where TT is the half-life). tt: Time elapsed. Example: If the decay constant (λλ) is 0.1 and the initial quantity is 100, how much remains after 20 units of time? N(20)=100⋅e−0.1⋅20=100⋅e−2≈13.53N(20)=100⋅e−0.1⋅20=100⋅e−2≈13.53
