Science Notes 2024 T4 PDF

**Matter, Atoms, and Atomic Structure** 1. **Definitions: Matter, Atom, Element**: - **Matter**: Anything that occupies space and has mass. It exists in various states: solid, liquid, gas, and plasma. - **Atom**: The smallest unit of an element that retains the proper...

**Matter, Atoms, and Atomic Structure** 1. **Definitions: Matter, Atom, Element**: - **Matter**: Anything that occupies space and has mass. It exists in various states: solid, liquid, gas, and plasma. - **Atom**: The smallest unit of an element that retains the properties of that element. An atom consists of a central nucleus made of protons and neutrons, surrounded by electrons in different energy levels or shells. - **Element**: A pure substance consisting of only one type of atom, characterized by a specific number of protons in its nucleus (atomic number). Examples include hydrogen, oxygen, and gold. 2. **Structure of an Atom**: - The atom is composed of three main subatomic particles: - **Protons**: Positively charged particles located in the nucleus. - **Neutrons**: Neutral particles also found in the nucleus. - **Electrons**: Negatively charged particles that orbit the nucleus in energy levels. - **Nucleus**: The dense central part of the atom where protons and neutrons reside. It contains most of the atom\'s mass. - **Electron Cloud**: Electrons move around the nucleus in defined energy levels (or shells). The first shell can hold up to 2 electrons, the second up to 8, and so on. 3. **Development of Atomic Models**: - **Dalton's Model**: Atoms are indivisible solid spheres. Atoms of the same element are identical, and different elements have different atoms. - **Thomson's Model (Plum Pudding Model)**: Discovered the electron and proposed that atoms are composed of a positively charged substance with negatively charged electrons scattered throughout, like \"plums\" in a pudding. - **Rutherford's Model**: Through the gold foil experiment, Rutherford discovered the nucleus. He suggested that atoms have a small, dense, positively charged nucleus with electrons orbiting the nucleus at a distance. - **Bohr's Model**: Bohr refined Rutherford's model by suggesting that electrons move in fixed orbits (energy levels) around the nucleus and that each orbit has a specific energy associated with it. Electrons can jump between these orbits by absorbing or emitting energy. 4. **Models in Science: Benefits and Limitations**: - **Benefits**: - Models simplify complex concepts, making them easier to understand and study. - They help scientists make predictions and develop new experiments. - They are visual aids that can help explain atomic theory to students and professionals. - **Limitations**: - Models are only approximations and do not represent the complete reality. - They often omit finer details to focus on essential features. - The Bohr model, for instance, does not fully explain electron behavior in atoms larger than hydrogen. **Atomic Numbers and Elements** 5. **Differences in Atomic Structure**: - Atoms of different elements vary based on the number of protons in their nucleus (atomic number). - For example, hydrogen has 1 proton, helium has 2 protons, and carbon has 6 protons. 6. **Periodic Table**: - The Periodic Table organizes elements based on their atomic number. - Each element is represented by a symbol (e.g., H for Hydrogen, O for Oxygen), and its atomic number (number of protons) is usually displayed at the top of the element's box. 7. **Mass Number and Neutrons**: - **Mass number** = Number of protons + Number of neutrons. - To determine the number of neutrons: - Subtract the atomic number from the mass number. - Example: Carbon-12 has 6 protons and 6 neutrons (12 -- 6 = 6 neutrons). 8. **Drawing Atomic Configurations**: - Use the periodic table to determine the number of protons, neutrons, and electrons for each element in the first 20. - Draw the nucleus with the correct number of protons and neutrons, then place electrons in their respective energy levels. 9. **Position of Metals and Non-metals on the Periodic Table**: - Metals are typically located on the left side and the center of the periodic table (e.g., groups 1-12). - Non-metals are located on the right side of the periodic table (e.g., groups 14-18). - Important groups to remember include: - **Alkali metals** (Group 1) - **Alkaline earth metals** (Group 2) - **Halogens** (Group 17) - **Noble gases** (Group 18) **Chemical Bonding and Compounds** 10. **Covalent vs Ionic Bonds**: - **Covalent Bonds**: Involve the sharing of electrons between two non-metal atoms. Example: Water (H₂O) where oxygen shares electrons with hydrogen. - **Ionic Bonds**: Involve the transfer of electrons from one atom (typically a metal) to another (typically a non-metal), forming ions. Example: Sodium chloride (NaCl) where sodium donates an electron to chlorine. 11. **Valency of Ions and Polyatomic Ions**: - Valency is the combining power of an element or ion. It represents the number of electrons an atom can lose, gain, or share in a chemical bond. - Learn the valencies for common polyatomic ions: - Hydroxide (OH-) = -1 - Nitrate (NO₃-) = -1 - Carbonate (CO₃²⁻) = -2 - Sulfate (SO₄²⁻) = -2 12. **Naming Ionic Compounds and Writing Formulas**: - For ionic compounds, the metal ion is written first, followed by the non-metal or polyatomic ion. - Example: NaCl = Sodium Chloride, MgSO₄ = Magnesium Sulfate. - When given the name of an ionic compound, determine the ions involved and write their respective charges to create the formula. 13. **Salt Formation**: - A salt is formed when a metal ion combines with a non-metal ion or a polyatomic ion. - Example: Sodium chloride (NaCl) is formed by the combination of sodium ions (Na⁺) and chloride ions (Cl⁻). 14. **Naming Covalent Compounds**: - Covalent compounds are named based on the number of atoms and the elements involved, using prefixes such as mono-, di-, tri-, etc. - Example: CO₂ = Carbon Dioxide, H₂O = Dihydrogen Monoxide (commonly known as water). **Acids, Bases, and Chemical Reactions** 15. **Acids and Bases in Everyday Life**: - **Acids**: Common examples include vinegar (acetic acid), lemon juice (citric acid), and stomach acid (hydrochloric acid). - **Bases**: Examples include baking soda (sodium bicarbonate) and household ammonia (ammonium hydroxide). 16. **Properties and Indicators**: - **Acids**: Sour taste, can corrode metals, pH less than 7. - **Bases**: Bitter taste, slippery to the touch, pH greater than 7. - **Indicators**: Substances used to test whether a solution is acidic or basic. - *Litmus paper*: Red in acid, blue in base. - *Universal indicator*: Shows a range of colors based on pH. 17. **Acid Strength**: - *Concentrated*: A large amount of acid in a small volume of water. - *Dilute*: A small amount of acid in a large volume of water. - *Strong Acid*: Completely ionizes in water (e.g., HCl). - *Weak Acid*: Only partially ionizes in water (e.g., acetic acid). 18. **Reactions with Acids**: - Metal + Acid → Salt + Hydrogen gas (e.g., Mg + HCl → MgCl₂ + H₂). - Metal Carbonate + Acid → Salt + Water + Carbon Dioxide (e.g., CaCO₃ + HCl → CaCl₂ + CO₂ + H₂O). - Acid + Base → Salt + Water (neutralization reaction). 19. **Hydrogen Pop Test**: - A lit splint makes a "pop" sound in the presence of hydrogen gas. 20. **Limewater Test for CO₂**: - Limewater turns milky when exposed to carbon dioxide gas, indicating the presence of CO₂. 21. **Chemical Reactions**: - Atoms are rearranged during chemical reactions but are neither created nor destroyed (Law of Conservation of Mass). 22. **pH Scale**: - The pH scale ranges from 0-14, with acids having a pH less than 7, bases having a pH greater than 7, and a pH of 7 being neutral (pure water). 23. **Constructing Word Equations**: - Represent chemical reactions using words rather than symbols. - Example: Hydrogen + Oxygen → Water. 24. **Chemical Reactions in Living Things**: - Respiration is a crucial chemical reaction that occurs in living organisms, converting glucose and oxygen into energy, water, and carbon dioxide. **Alfred Wegener's Theory of Continental Drift and Plate Tectonics** 1. **Wegener's Continental Drift Theory**: - Proposed that continents were once part of a single large landmass (Pangaea) that broke apart and drifted to their current positions. 2. **Evidence for Continental Drift**: - Similarities in the shapes of continents (e.g., South America and Africa appear to fit together). - Fossil evidence showing the same species on continents now separated by oceans. - Similar rock formations and mountain ranges on different continents. 3. **Hess's Seafloor Spreading Hypothesis**: - Harry Hess proposed that new seafloor is created at mid-ocean ridges and spreads outward, pushing older seafloor away from the ridge. 4. **Evidence Supporting Seafloor Spreading**: - Magnetic striping on the ocean floor shows alternating patterns of normal and reversed magnetic polarity, recording Earth\'s magnetic field reversals. - The age of rocks increases as you move away from mid-ocean ridges. - The thickness of ocean floor sediments increases with distance from the ridge, suggesting seafloor spreading over time. 5. **Plate Tectonics Theory**: - Earth's lithosphere is divided into tectonic plates that move due to the convection currents in the mantle. - The movement of these plates explains continental drift, earthquakes, volcanic activity, and the formation of mountain ranges. 6. **Mechanisms Driving Plate Movement**: - *Mantle Convection*: Heat from Earth\'s core causes convection currents in the mantle, which move tectonic plates. - *Gravitational Forces*: Ridge push and slab pull also contribute to plate movement. - *Ridge Push*: Newly formed rock at mid-ocean ridges pushes plates apart. - *Slab Pull*: Denser oceanic plates sink into the mantle at subduction zones, pulling the rest of the plate along. 7. **Types of Plate Boundaries**: - *Divergent Boundaries*: Plates move apart. New crust forms at mid-ocean ridges (e.g., Mid-Atlantic Ridge). - *Convergent Boundaries*: Plates move toward each other. This can result in mountain formation or subduction (e.g., Himalayas, Andes). - *Transform Boundaries*: Plates slide past each other, leading to earthquakes (e.g., San Andreas Fault). 8. **Interactions at Plate Boundaries**: - Convergent boundaries can result in the formation of volcanoes, mountain ranges, and ocean trenches. - Divergent boundaries are associated with the creation of new oceanic crust. - Transform boundaries are associated with frequent earthquakes due to friction between plates. 9. **Earthquakes and Plate Boundaries**: - Earthquakes occur when stress builds up along faults or plate boundaries and is suddenly released. - The *focus* is the point inside Earth where the earthquake originates. - The *epicenter* is the point on Earth's surface directly above the focus. 10. **P-Waves and S-Waves**: - **P-Waves (Primary Waves)**: Fastest seismic waves; they compress and expand the ground like sound waves. Travel through both solids and liquids. - **S-Waves (Secondary Waves)**: Slower than P-waves; they move the ground up and down or side to side. Only travel through solids. - The time difference between P-wave and S-wave arrivals helps locate an earthquake's epicenter. 11. **Earthquake Magnitude**: - Measured on the **Richter scale**. Each increase in number represents a tenfold increase in magnitude (energy released). 12. **Volcanic Activity at Hot Spots**: - Hot spots are areas where plumes of hot magma rise through the mantle to create volcanoes, independent of plate boundaries (e.g., Hawaii). 13. **Tsunamis**: - Tsunamis are large sea waves generated by underwater earthquakes or volcanic eruptions, displacing large amounts of water. **Electricity and Circuits** 1. **Conductors, Insulators, and Resistors**: - **Conductors**: Materials that allow electric current to flow easily (e.g., metals like copper and aluminum). - **Insulators**: Materials that resist the flow of electricity (e.g., rubber, plastic). - **Resistors**: Devices that limit the flow of current in a circuit. They convert electrical energy into heat. 2. **Voltage, Current, and Resistance**: - **Voltage (V)**: The potential difference that drives electric current through a circuit. Measured in volts (V). - **Current (I)**: The flow of electric charge through a conductor. Measured in amperes (A). - **Resistance (R)**: The opposition to the flow of current. Measured in ohms (Ω). 3. **Ohm's Law**: - Ohm's law relates voltage (V), current (I), and resistance (R) in a circuit: V = IR. - Example: If a resistor has a resistance of 10Ω and the voltage across it is 5V, the current flowing through the resistor is I = V/R = 5V/10Ω = 0.5A. 4. **Series and Parallel Circuits**: - **Series Circuit**: A single path for current to flow. If one component fails, the entire circuit is interrupted. - **Parallel Circuit**: Multiple paths for current to flow. If one component fails, other parts of the circuit continue to work. 5. **Circuit Components**: - **Ammeter**: Measures the current in a circuit and is connected in series with the circuit. - **Voltmeter**: Measures the voltage across a component and is connected in parallel with the component. 6. **Behaviour of Voltage, Current, and Resistance**: - In a series circuit, the total voltage is divided across the components, while the current remains the same throughout. - In a parallel circuit, the voltage remains the same across all branches, but the current divides among the branches. 7. **Applications of Series and Parallel Circuits**: - **Series Circuits**: Often used in simple applications like flashlights. - **Parallel Circuits**: Used in household wiring to ensure that appliances work independently of each other.