## AQA GCSE Chemistry Paper 1 Study Notes: Topics 1-5 These notes cover AQA GCSE Chemistry Paper 1, encompassing Topics 1-5: Atoms, Bonding, Quantitative Chemistry, and Chemical and Energy Changes. Content is relevant for Higher and Foundation Tier, Double Award, Combined Trilogy, and Triple Award students. Triple-only content will be clearly indicated. ### I. Atoms and the Periodic Table * **Substances:** Everything is made of atoms. Different types of atoms are called **elements**, represented by symbols on the **periodic table**. The periodic table organizes elements by atomic number and recurring chemical properties. * **Compounds:** Substances containing two or more different types of atoms chemically bonded. Example: Water ($H_2O$) – two hydrogen atoms for every oxygen atom. If no number follows a symbol, it's assumed to be 1. The chemical formula for carbon dioxide is $CO_2$. This means one carbon atom is bonded to two oxygen atoms. * **Chemical Reactions:** Atoms rearrange their bonds during chemical reactions. These can be represented by **word equations** and **balanced chemical equations**. When balancing equations, start with atoms found only in one compound on each side. Balancing the equation for methane combustion: $CH_4 + O_2 \rightarrow CO_2 + H_2O$. The balanced equation is $CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O$ * **Mixtures:** Combinations of elements and compounds not chemically bonded. Examples: Air (oxygen, nitrogen, etc.), saltwater (water and sodium chloride). * **Separating Mixtures:** * **Filtration:** Separates insoluble solids from liquids (e.g., sand from water). * **Crystallization:** Separates soluble solids from liquids by evaporation (e.g., salt from water). * **Distillation:** Separates liquids based on boiling points (e.g., separating water from salt). * **Fractional Distillation:** Separates mixtures of liquids with different boiling points. Filtration, crystallization, distillation, and fractional distillation are all physical changes, not chemical reactions. * **States of Matter:** Solids (particles vibrate in fixed positions), liquids (particles move past each other), gases (particles far apart, move randomly, most energy). Gases are compressible; solids and liquids are not. Confusing physical and chemical changes. Physical changes don't create new substances; chemical changes do. * **State Symbols:** (s) solid, (l) liquid, (g) gas, (aq) aqueous (dissolved in water). * **Atomic Models:** * **Thomson's Plum Pudding Model:** Positive charge with embedded electrons. * **Rutherford's Nuclear Model:** Mostly empty space with a small, dense, positively charged nucleus and orbiting electrons. * **Bohr's Model:** Electrons in specific energy levels or shells. * **Chadwick's Discovery:** Neutrons in the nucleus. * **Subatomic Particles:** * **Protons:** Positive charge (+1), relative mass of 1. * **Neutrons:** Neutral charge (0), relative mass of 1. * **Electrons:** Negative charge (-1), negligible mass. * **Atomic Number:** Number of protons (determines the element). * **Mass Number (RAM):** Number of protons + neutrons. * **Isotopes:** Atoms of the same element with different numbers of neutrons (same atomic number, different mass number). * **Relative Atomic Mass:** Average mass of all isotopes of an element, weighted by their abundance. Calculating average relative atomic mass: If 75% of chlorine atoms have a mass of 35 and 25% have a mass of 37, the average relative atomic mass is (0.75 * 35) + (0.25 * 37) = 35.5 * **Electron Configuration:** Arrangement of electrons in shells (2, 8, 8, 2...). Magnesium (12 electrons): 2, 8, 2 * **Periodic Table Groups:** * **Group 1 (Alkali Metals):** 1 outer electron, highly reactive. Reactivity increases down the group. * **Group 7 (Halogens):** 7 outer electrons, reactive. Reactivity decreases down the group. * **Group 0 (Noble Gases):** Full outer shell, unreactive. * **Ions:** Atoms that have gained or lost electrons (charged particles). Metals form positive ions (cations); non-metals form negative ions (anions). ### II. Bonding * **Metallic Bonding:** Lattice of positive ions surrounded by delocalized electrons. Explains conductivity and malleability of metals. * **Ionic Bonding:** Transfer of electrons between metals and non-metals to form ions with full outer shells. Ionic compounds have high melting points and boiling points and conduct electricity when molten or dissolved. Formation of sodium chloride ($NaCl$): Sodium ($Na$) loses one electron to become $Na^+$, and chlorine ($Cl$) gains one electron to become $Cl^−$. * **Covalent Bonding:** Sharing of electrons between non-metal atoms to achieve full outer shells. Simple covalent molecules have low melting and boiling points and do not conduct electricity. Formation of chlorine ($Cl_2$): Each chlorine atom shares one electron with the other. * **Giant Covalent Structures:** Atoms covalently bonded in a large network (e.g., diamond, graphite). High melting points and boiling points. Graphite conducts electricity due to delocalized electrons. * **Allotropes:** Different forms of the same element (e.g., diamond, graphite, fullerenes). * **Nanoparticles:** Tiny particles with a large surface area to volume ratio. ### III. Quantitative Chemistry * **Conservation of Mass:** Total mass of reactants = total mass of products. * **Relative Formula Mass (RFM):** Sum of relative atomic masses of atoms in a compound. * **The Mole:** A unit for measuring the amount of substance. One mole of a substance has a mass in grams equal to its relative atomic or formula mass. Use the formula: Moles = mass (g) / RFM * **Stoichiometry:** The ratio of moles of reactants and products in a balanced chemical equation. In the reaction $2H_2 + O_2 \rightarrow 2H_2O$, the stoichiometry is 2:1:2 (hydrogen:oxygen:water). * **Limiting Reactant:** The reactant that is completely used up first in a reaction, limiting the amount of product formed. * **Concentration:** Amount of solute per unit volume of solution (g/dm³ or mol/dm³). Remember to convert volumes to dm³ (divide cm³ by 1000). * **Percentage Yield:** (Actual yield / Theoretical yield) x 100%. * **Atom Economy:** (RFM of desired product / Total RFM of reactants) x 100%. ### IV. Chemical Changes * **Reactivity Series:** A list of metals in order of their reactivity. More reactive metals displace less reactive metals from their compounds. * **Extraction of Metals:** Metals less reactive than carbon can be extracted using carbon (smelting). * **Oxidation and Reduction:** * **Oxidation:** Loss of electrons. * **Reduction:** Gain of electrons. * **OIL RIG:** Oxidation Is Loss, Reduction Is Gain. * **Reactions with Acids:** More reactive metals than hydrogen displace hydrogen from acids. * **Neutralization:** Reaction between an acid and an alkali to produce a salt and water. * **pH Scale:** Measures acidity or alkalinity (0-14). Strong acids and alkalis fully dissociate; weak acids and alkalis partially dissociate. * **Titration:** A technique used to determine the concentration of an acid or alkali. (Triple only) ### V. Energy Changes * **Exothermic Reactions:** Release energy (temperature increase). * **Endothermic Reactions:** Absorb energy (temperature decrease). * **Energy Profile Diagrams:** Show the energy changes during a reaction, including activation energy. * **Bond Energies:** Energy required to break or released when forming a chemical bond. Can be used to calculate the overall energy change in a reaction. (Triple only) * **Electrolysis:** Using electricity to decompose ionic compounds. Cations are reduced at the cathode; anions are oxidized at the anode. (Triple only) * **Cells and Batteries:** Devices that convert chemical energy into electrical energy. (Triple only) * **Hydrogen Fuel Cells:** Convert chemical energy from hydrogen and oxygen into electrical energy. (Triple only) This comprehensive overview should provide a solid foundation for your AQA GCSE Chemistry Paper 1 exam preparation. Remember to practice applying these concepts through past papers and additional exercises. Good luck!