France Troisième Physics-Chemistry
Chapters: 4
1. Matter and its changes
Atom, nucleus and ions · Acidic and basic solutions, pH · Reading reaction equations, conservation · Tests for ions and substances · Elements on Earth and in the Universe
- 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.
- 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.
- 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.
- Tests for Ions: Flame Tests, Hydroxide Precipitates, Anion Tests and Flame Emission Spectroscopy – An ionic compound is made of a positive metal ion and a negative ion. Each can be found with its own test. Flame tests show metal ions by colour: lithium crimson, sodium yellow, potassium lilac, calcium orange-red, copper green. Sodium hydroxide gives coloured hydroxide precipitates: Cu²⁺ blue, Fe²⁺ green, Fe³⁺ brown, Al³⁺, Ca²⁺ and Mg²⁺ white (only Al(OH)₃ dissolves in excess). Carbonates fizz with acid and the gas turns limewater milky. Halides with acidified silver nitrate: chloride white, bromide cream, iodide yellow. Sulfates with acidified barium chloride: white precipitate. Instruments such as flame emission spectroscopy are faster, more sensitive and can measure amounts.
2. Motion and interactions
Gravitation and weight
- Newton's Universal Law of Gravitation – Every mass in the universe pulls every other mass. The pull between two point masses m₁ and m₂ a distance r apart is F = G m₁ m₂ / r². It acts along the line joining them. The two bodies pull each other with equal and opposite forces. G = 6.67 × 10⁻¹¹ N m² kg⁻² is the same everywhere, so it is called the universal gravitational constant. When many masses pull one body, the forces add as vectors (superposition).
3. Energy
Kinetic and potential energy, conservation · Electrical power and energy · Energy sources, transfers and conversions
- Work, Energy and Power – Work is done when a force moves an object: W = F × s, measured in joules (J). Energy is the ability to do work. A moving body has kinetic energy ½mv²; a raised body has potential energy mgh. Energy is never made or destroyed, only changed from one form to another. Power is how fast work is done: P = W ÷ t, in watts. Simple machines like levers and pulleys let a small effort move a big load.
- Electric Power and Electrical Energy – Electric power is the rate of using electrical energy: P = VI = I²R = V²/R, in watts. Energy used = power × time. At home energy is measured in kilowatt-hours: 1 kWh = 1 unit = 3.6 × 10⁶ J. Bill = units × rate.
- Minerals and Energy Resources – Minerals are natural substances found in rocks. They are metallic (ferrous or non-ferrous), non-metallic, or energy minerals. Energy comes from conventional sources like coal, petroleum, natural gas and electricity, and from non-conventional sources like sun, wind, nuclear, biogas, tides and heat from the Earth. Both minerals and energy must be conserved.
4. Signals
Light, sound and radio signals carry information
- Sound – Sound is made by vibrating objects. It travels through a medium (air, water, solids) as a longitudinal wave: particles move back and forth, making crowded parts (compressions) and spread-out parts (rarefactions). Frequency (Hz) sets the pitch, amplitude sets the loudness, and speed v = f × λ. Sound cannot travel in vacuum. Humans hear 20 Hz to 20,000 Hz; below is infrasound, above is ultrasound. Reflected sound gives echoes, used and controlled in buildings.