Science 7 Past Paper PDF

Scientific Models-Particle Model of Matter The Particle Model of Matter is fundamental in understanding physical and chemical processes. According to this model, all matter is composed of small particles—atoms or molecules—that are in constant motion. Dalton’s Atomic Theory, a cornerstone of this mo...

Scientific Models-Particle Model of Matter The Particle Model of Matter is fundamental in understanding physical and chemical processes. According to this model, all matter is composed of small particles—atoms or molecules—that are in constant motion. Dalton’s Atomic Theory, a cornerstone of this model, posits that all matter is made of indivisible atoms, which combine in fixed ratios to form compounds. Modern interpretations include quantum mechanics, which reveals that atoms are not indivisible but composed of subatomic particles, and their behavior can be influenced by forces at quantum levels. This model helps explain the properties of gases, liquids, and solids, as well as phenomena like diffusion and phase changes. John Dalton (1766–1844): Proposed Dalton’s Atomic Theory, which introduced the concept of atoms as indivisible particles that combine to form compounds in fixed ratios. J.J. Thomson (1856–1940): Discovered the electron in 1897, leading to the Plum Pudding Model, which suggested that atoms are made of a positive ”soup” with embedded electrons. Ernest Rutherford (1871–1937): Conducted the gold foil experiment in 1909, which led to the Rutherford Model, proposing a dense, positively charged nucleus surrounded by orbiting electrons. Niels Bohr (1885–1962): Introduced the Bohr Model in 1913, which described electrons orbiting the nucleus at fixed energy levels, explaining atomic spectra. Werner Heisenberg (1901–1976): Developed Quantum Mechanics and the Uncertainty Principle, which refined the understanding of electron behavior in atoms. Erwin Schrödinger (1887–1961): Created the Schrödinger Equation in 1926, leading to the development of quantum mechanical models of the atom, including electron cloud models. James Chadwick (1891–1974): Discovered the neutron in 1932, which, along with protons, forms the atomic nucleus. These scientists collectively advanced our understanding of atomic structure, evolving from indivisible atoms to complex quantum models. Elements and Compounds Elements Definition: Elements are pure substances consisting of only one type of atom. They cannot be broken down into simpler substances by chemical means. Each element is defined by its atomic number, which is the number of protons in its nucleus. Classification: Elements are categorized into metals, nonmetals, and metalloids based on their properties. Metals are typically conductive and malleable; nonmetals are often insulators and can be gases or solids; metalloids have properties intermediate between metals and nonmetals. Periodic Table: Elements are arranged in the Periodic Table, which organizes them by increasing atomic number and recurring chemical properties. This arrangement helps predict element behavior and relationships. Compounds Definition: Compounds are substances formed from two or more different elements chemically bonded together. They have properties distinct from their constituent elements. Types of Bonds: Compounds are formed through different types of chemical bonds: Ionic Bonds: Occur between metals and nonmetals where electrons are transferred, forming positively and negatively charged ions (e.g., sodium chloride, NaCl). Covalent Bonds: Form between nonmetals where electrons are shared to achieve stability (e.g., water, H₂O). Metallic Bonds: Involve a “sea of electrons” shared among metal atoms, contributing to properties like conductivity (e.g., iron, Fe). Chemical Formulas: Compounds are represented by chemical formulas that indicate the types and numbers of atoms involved. For example, H₂O denotes water, with two hydrogen atoms and one oxygen atom. Properties: Compounds have unique properties compared to the elements from which they are made. For instance, table salt (NaCl) is essential for flavor but is toxic in its elemental forms. Summary Elements are the building blocks of matter, each with unique properties and atomic structure. Compounds are formed from these elements through chemical reactions, resulting in substances with new properties. Understanding both elements and compounds is crucial for studying chemistry and materials science. The Kinetic Molecular Theory The Kinetic Molecular Theory (KMT) of matter describes how particles in gases, liquids, and solids behave: Particles in Motion: All matter is composed of tiny particles (atoms, molecules, or ions) that are in constant, random motion. Energy and Speed: The temperature of a substance is a measure of the average kinetic energy of its particles. Higher temperatures mean higher average speeds and kinetic energy. Elastic Collisions: Particles collide with each other and with the walls of their container. These collisions are elastic, meaning total kinetic energy is conserved. States of Matter Gases: Particles are far apart, move quickly, and collide frequently but are not influenced by intermolecular forces. This results in gases expanding to fill their container. Liquids: Particles are closer together and have some attractive forces. They move more slowly than in gases but can still flow, taking the shape of their container while maintaining a fixed volume. Solids: Particles are tightly packed in a fixed position with strong intermolecular forces. They vibrate in place but do not move freely, giving solids a definite shape and volume. Applications: Pressure and Volume: KMT helps explain gas laws such as Boyle’s Law (pressure-volume relationship) and Charles’s Law (temperature-volume relationship). Diffusion: The theory accounts for the spreading of particles from regions of higher concentration to lower concentration due to their constant motion. Overall, KMT provides a fundamental understanding of how particle motion affects the physical properties of matter and explains the behavior of substances under various conditions. States of Matter and their Particle Arrangement Solid Particle Arrangement: Particles are closely packed in a fixed, orderly arrangement. They vibrate in place but do not move around. Particle Movement: Particles vibrate around fixed positions. This limited movement gives solids their rigid structure and fixed shape. Properties: Definite shape and volume. Solids are incompressible and usually have high density. Liquid Particle Arrangement: Particles are close together but not in a fixed position. They can move around each other, allowing liquids to flow. Particle Movement: Particles slide past each other, which allows liquids to flow and take the shape of their container while maintaining a constant volume. Properties: Definite volume but no definite shape; liquids take the shape of their container. They are relatively incompressible and have a moderate density. Gas Particle Arrangement: Particles are far apart and move freely at high speeds. They fill the entire volume of their container. Particle Movement: Particles move rapidly and randomly, filling any container they are in and spreading out to fill the space available. Properties: No definite shape or volume; gases expand to fill the shape and volume of their container. They are compressible and have low density compared to solids and liquids. Plasma Particle Arrangement: Consists of ions and free electrons. The particles move rapidly and are not in any fixed arrangement. Particle Movement: Particles (ions and electrons) move extremely fast and interact with each other and with electromagnetic fields. Properties: No definite shape or volume. Plasmas are highly conductive and are found in stars and some types of flames. Phase Change Melting: Solid to liquid Freezing: Liquid to solid Vaporization: Liquid to gas (including boiling and evaporation) Condensation: Gas to liquid Sublimation: Solid to gas Deposition: Gas to solid Steps in Scientific Investigation Observation Description: Start by observing the natural world or a specific phenomenon. Gather information through your senses or instruments. Purpose: To identify a problem or question that needs to be answered. Question Description: Formulate a clear and focused question based on the observations. Purpose: To define what you are trying to understand or solve. Research Description: Conduct background research to gather existing information related to your question. This involves reviewing scientific literature, previous studies, and relevant data. Purpose: To build on existing knowledge and refine your question or hypothesis. Hypothesis Description: Develop a testable and falsifiable hypothesis, which is an educated guess or prediction about the outcome of your investigation. Purpose: To provide a basis for designing experiments and making predictions. Experiment Description: Design and conduct experiments to test the hypothesis. This involves creating a procedure, selecting materials, and ensuring controlled conditions. Purpose: To gather empirical data that will either support or refute the hypothesis. Data Collection Description: Collect and record data systematically during the experiment. Use appropriate tools and methods for accurate measurements. Purpose: To obtain reliable and valid data for analysis. Analysis Description: Analyze the collected data to determine if it supports or contradicts the hypothesis. This may involve statistical analysis or graphical representation. Purpose: To interpret the data and draw conclusions about the hypothesis. Conclusion Description: Based on the data analysis, determine whether the hypothesis is supported or not. Discuss the implications of the findings. Purpose: To summarize the results and their significance, and to suggest potential further research. Communication Description: Share the results with the scientific community and the public through reports, presentations, or publications. Purpose: To contribute to the body of scientific knowledge and allow others to review, replicate, or build upon your work. Revision Description: Reflect on the investigation process and results. Revise the hypothesis or experimental design if necessary and consider new questions or experiments. Purpose: To refine and improve scientific understanding and investigation methods. These steps are often iterative; new observations or results can lead to further questions and experiments, enhancing the overall scientific knowledge base. Solute, Solution, and Solubility Solution Definition: A solution is a homogeneous mixture of two or more substances where the solute is evenly distributed within the solvent. It has a uniform composition throughout. Solute Definition: A solute is a substance that is dissolved in a solvent to form a solution. It is usually present in a smaller amount compared to the solvent. Examples: Salt in saltwater, sugar in tea, or oxygen in air. Solvent Definition: The substance in which the solute dissolves (usually present in a greater amount) Examples: water, alcohol, or oil. Solubility Definition: Solubility is the maximum amount of a solute that can dissolve in a given quantity of solvent at a specific temperature and pressure, resulting in a saturated solution. Factors Affecting Solubility Temperature: Generally, solubility increases with temperature for most solid solutes, but decreases for gases. Pressure: For gases, solubility increases with pressure. Nature of Solute and Solvent: Solubility also depends on the chemical nature of the solute and solvent (e.g., polar solutes dissolve well in polar solvents). Understanding these concepts helps in various applications, from making drinks to industrial processes. Safety Precautions in the Laboratory In any laboratory, safety precautions are critical to prevent accidents and ensure a safe working environment. Here’s a review of key safety practices: Personal Protective Equipment (PPE): Always wear appropriate PPE such as lab coats, safety goggles, and gloves to protect against chemical splashes, spills, and other hazards. Proper Training: Ensure all personnel are properly trained in laboratory procedures and emergency protocols. Understanding how to handle equipment and chemicals correctly is crucial. Chemical Safety: Store chemicals according to their compatibility and hazard classification. Always label containers clearly and use fume hoods when working with volatile substances. Equipment Safety: Regularly inspect and maintain laboratory equipment. Follow proper usage guidelines and report any malfunctions immediately. Emergency Procedures: Be familiar with the location and proper use of emergency equipment like eyewash stations, safety showers, and fire extinguishers. Know the evacuation routes and emergency contact numbers. Housekeeping: Keep work areas clean and organized. Dispose of waste materials properly and promptly. Spills should be cleaned up immediately using appropriate procedures. Handling Biological Materials: Follow protocols for handling and disposing of biological specimens to avoid contamination and exposure. By adhering to these safety practices, you can help ensure a secure and efficient laboratory environment.