Russia 8 класс Chemistry (advanced)
Chapters: 3
1. First chemical concepts
Chemistry and its history · Laboratory and mixtures · Atomic-molecular theory · Formula, valency, mole · Chemical reactions
- Mixtures and Their Separation – A mixture has two or more substances mixed without any fixed ratio, and each keeps its own properties. Homogeneous mixtures (solutions) look the same everywhere; heterogeneous ones do not. By particle size we get solutions (< 1 nm), colloids (1–1000 nm) and suspensions (> 1000 nm). Colloids scatter light (Tyndall effect). Concentration tells how much solute is in a solution. We separate mixtures by using a difference in their parts: evaporation, crystallisation, distillation, chromatography, sublimation, centrifugation and coagulation.
- Atoms and Molecules – In a chemical reaction mass is neither created nor destroyed (conservation of mass), and a compound always has its elements in the same ratio by mass (constant proportions). Dalton explained both: matter is made of tiny atoms that join in small whole numbers. Atoms join to form molecules; charged atoms or groups are ions. Formulae are written by crossing valencies. Molecular mass (or formula unit mass for ionic compounds) is the sum of the atomic masses in the formula, in u.
- Chemical Reactions and Balancing Equations – In a chemical reaction atoms are not made or destroyed; they only change partners. So a chemical equation must have the same number of each kind of atom on both sides. We balance it by changing the numbers in front of formulas, never the formulas themselves.
2. Key inorganic substances
Gases and Avogadro's law · Oxygen and oxidation · Thermal effect and fuel · Hydrogen · Water and solutions · Oxides · Acids · Bases · Salts · Genetic link of classes
- Avogadro's Law: Equal Volumes, Equal Numbers of Molecules – Avogadro's law: at the same temperature and pressure, equal volumes of all gases hold the same number of molecules. So volume is proportional to the number of moles: V ∝ n, or V₁/n₁ = V₂/n₂. At STP (0 °C, 101.3 kPa) one mole of any gas fills 22.4 L (molar volume, Vm). Useful links: n = V ÷ Vm, N = n × 6.02 × 10²³, m = n × M. Equal volumes have different masses, so relative density D = M₁ ÷ M₂ (D by hydrogen = M ÷ 2; by air = M ÷ 29). In gas reactions, volumes are in the same ratio as the equation coefficients (2H₂ + O₂ → 2H₂O: 2 : 1 : 2).
- Oxygen – Oxygen (O, atomic number 8) is a colourless, odourless gas that makes up about 21% of air by volume. It exists as O₂ molecules. In the lab it is made by breaking down hydrogen peroxide with a manganese dioxide catalyst (2H₂O₂ → 2H₂O + O₂) or by heating potassium manganate(VII); in industry it comes from fractional distillation of liquid air. It relights a glowing splint. Oxygen supports burning and respiration and reacts with most elements to form oxides: metal oxides are basic, non-metal oxides are mostly acidic. Its other form, ozone (O₃), shields Earth from UV rays.
- Types of Chemical Reactions – Most reactions fit a few patterns. Combination: A + B → AB. Decomposition: AB → A + B. Displacement: A + BC → AC + B, where the more reactive A pushes out B. Double displacement: AB + CD → AD + CB, where partners swap; if an insoluble solid forms it is a precipitation reaction. Reactions that give out heat are exothermic; those that take in heat are endothermic.
- Hydrogen: The Lightest Element – Hydrogen (H) is element 1: one proton and one electron. It exists as H₂ molecules, a colourless, odourless gas that is the least dense of all gases and hardly dissolves in water. In the lab it is made from a reactive metal and a dilute acid (Zn + 2HCl → ZnCl₂ + H₂) and collected over water. It burns with a squeaky pop to form only water. It reacts with non-metals to give hydrides such as HCl, NH₃ and H₂S, and it reduces some metal oxides. It has three isotopes: protium, deuterium and tritium. Uses: ammonia and fertilisers, margarine, rocket fuel and clean fuel cells.
- Solutions: How Things Dissolve and How Much Can Dissolve – A solution is a uniform mixture of a solute dissolved in a solvent. In water (an aqueous solution) the solute breaks into particles too small to see, so it never settles and passes through filter paper. Concentration tells how much solute is present (mass % = solute ÷ solution × 100). Solubility is the most that can dissolve in 100 g of solvent at a given temperature; beyond it the solution is saturated. Evaporation, crystallisation and distillation separate solutions.
- Acids and Bases: Properties, Indicators and Reactions – An acid gives H⁺ ions in water and a base gives OH⁻ ions. Indicators show which one is present by a colour or smell change, and when H⁺ meets OH⁻ they make water, leaving a salt behind.
3. Periodic law, atom, bonding
Periodic law and table · Atomic structure and orbitals · Chemical bonding · Crystals · Redox reactions
- Periodic Classification of Elements – Scientists sorted elements so that similar ones sit together. Döbereiner made triads, Newlands found that every 8th element repeats (octaves), Mendeleev arranged elements by atomic mass and left gaps for unknown ones. Moseley showed that atomic number is the real key. Modern periodic law: the properties of elements are a periodic function of their atomic numbers. The modern table has 7 periods and 18 groups. Elements with Z > 100 get temporary IUPAC names built from digit roots (nil, un, bi, tri, quad, pent, hex, sept, oct, enn) plus -ium.
- Structure of the Atom – An atom has a tiny, heavy, positive nucleus made of protons and neutrons. Electrons move around it in fixed shells K, L, M, N. The number of protons (Z) tells the element; protons + neutrons give the mass number (A). Outer electrons decide valency. Isotopes share Z; isobars share A.
- Ionic Compounds: How Metals and Non-metals React – A metal atom gives its outer electrons to a non-metal atom so that both get a full outer shell (octet). The metal becomes a positive ion (cation), the non-metal a negative ion (anion), and the strong pull between them is an ionic (electrovalent) bond. Ionic compounds are hard crystalline solids with high melting points, dissolve in water, and conduct electricity only when molten or dissolved.
- Oxidation and Reduction: Corrosion and Rancidity – Oxidation is gain of oxygen (or loss of hydrogen); reduction is loss of oxygen (or gain of hydrogen). They always happen together, so these are called redox reactions. The substance that gives oxygen is the oxidising agent; the one that takes it is the reducing agent. In daily life, oxidation causes corrosion (like rusting of iron) and rancidity (fats and oils going stale).