Spain 3º ESO Physics and Chemistry

Chapters: 5

1. Basic scientific skills

Scientific research methods · Experimental work and projects · Science learning environments · Lab and safety rules · Scientific language and SI units · Interpreting scientific information · Scientific culture and scientists

The Scientific Method – The scientific method is the careful way scientists find out how the world works. Observe something, ask a testable question, make a hypothesis (a clear, testable guess), test it with a fair experiment (change one variable, measure one, keep the rest the same), repeat and record data, analyse it, draw a conclusion and share it so others can check. Results that fail the test are useful too: they send you back to a new hypothesis.
Research Skills: From a Question to a Finished Project – Research is a careful way of finding an answer. You ask a clear, focused question, plan how to answer it, find information and check that each source can be trusted, collect and analyse your own data, draw a conclusion that the evidence supports, and share it while crediting every source you used.
Lab Safety and Safe Experiments – Dress for safety (goggles, coat, closed shoes, hair tied). Read labels and hazard pictograms. Heat gently with the mouth of the tube pointing away. Add acid to water, waft smells, never taste. Report every accident at once. Plan experiments step by step, assess the risks first and dispose of waste correctly.
Measurement and Units: How We Measure Anything – To measure something is to compare it with a fixed amount called a unit. Every measurement has a number and a unit. Scientists everywhere use the SI system, with seven base units such as the metre, kilogram and second. Prefixes like kilo (×1000), centi (÷100) and milli (÷1000) make units bigger or smaller. A good measurement starts at zero, is read with the eye straight above the mark, and is only as accurate as the smallest division (least count). Rounded values hide a small range, given by upper and lower bounds.
Media Literacy – Media literacy is the skill of reading, questioning and creating media: news, ads, videos, posts, films and games. Every media text is made by someone, for a purpose, for an audience, using forms, conventions and techniques that shape how we feel. A media-literate person checks the source, evidence, other coverage and the original before believing or sharing, notices bias and filter bubbles, and makes their own media responsibly.
History of Science: How Our Ideas About Nature Changed – Science grew slowly over 5,000 years. Early civilisations watched the sky to make calendars. Greek thinkers asked why things happen and used reason. Indian and Islamic scholars gave us zero, algebra and careful experiments. In the Scientific Revolution, Copernicus, Galileo and Newton replaced the Earth-centred model with a Sun-centred one and tested ideas by experiment. Modern science brought atoms, evolution, relativity and quantum theory. Each step shows the same lesson: good evidence can overturn old ideas.

2. Matter

Kinetic molecular theory · Material systems experiments · Atomic structure and periodic table · Main chemical compounds · Chemical nomenclature

The Particle Model of Matter – All matter is made of tiny particles that are always moving. In a solid they are close and only vibrate; in a liquid they are close but slide past each other; in a gas they are far apart and move fast in all directions. Heating gives particles more energy: either they move faster (temperature rises) or the forces between them are broken (the state changes while the temperature stays the same). Gas pressure comes from particles hitting the walls.
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.
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.
Chemical Bonding: Ionic, Covalent and Metallic Bonds – Atoms join together (bond) to become more stable. Only their outer electrons take part. Most atoms are most stable with 8 outer electrons: the octet rule. There are three main ways to reach it. In an ionic bond, a metal gives electrons to a non-metal, making oppositely charged ions that attract. In a covalent bond, two non-metals share pairs of electrons to make molecules. In a metallic bond, metal atoms release outer electrons into a shared 'sea' that holds positive ions together. The difference in electronegativity (how strongly an atom pulls shared electrons) tells us which kind of bond forms. The type of bond explains melting points, whether a substance conducts electricity, and whether it dissolves in water.
Kossel-Lewis Approach and the Ionic Bond – Atoms join so that each gets a stable outer shell of 8 electrons (an octet), like a noble gas. Kossel said atoms can give or take electrons to make ions (ionic bond). Lewis said atoms can also share pairs of electrons (covalent bond). Lewis structures show these electrons as dots and lines. Formal charge (V − L − B/2) helps pick the best Lewis structure. Ions pack into a crystal, and the energy released is linked to the lattice enthalpy.
IUPAC Nomenclature and Isomerism of Organic Compounds – Millions of organic compounds exist, so every one needs a clear, unique name. The IUPAC system builds a name from three parts: the word root (number of carbons in the main chain), the suffix (type of bond and main functional group) and the prefixes (side groups). You pick the longest chain that holds the main group, number it so the main group and branches get the lowest numbers, and write side groups in alphabetical order. Isomers are compounds with the same molecular formula but different arrangement. Structural isomers differ in how atoms are joined (chain, position, functional group, metamerism). Stereoisomers are joined the same way but differ in 3D arrangement (geometrical cis/trans and optical isomers).

3. Energy

What energy is · Energy uses and transformations · Renewable and non-renewable sources · Effects of heat on matter · Electrical nature of matter

Energy Stores and Transfers – Energy is what makes things change. It is kept in stores (chemical, kinetic, gravitational, elastic, thermal, magnetic, electrostatic, nuclear) and moves between them by four pathways: a force doing work, an electric current, heating and radiation (light, sound). Energy is measured in joules (J). It is never made or destroyed; it only moves. Some always spreads out as heat, so no machine is 100% efficient.
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.
Temperature – Temperature tells us how hot or cold something is. Inside every object, tiny particles are always moving; temperature measures their average kinetic energy (how fast they jiggle on average). We measure it with a thermometer, in degrees Celsius (°C), kelvin (K, the SI unit) or degrees Fahrenheit (°F). K = °C + 273 and °F = 9/5 × °C + 32. The lowest possible temperature is absolute zero, 0 K = −273 °C. When a hot and a cold object touch, heat flows from hot to cold until both have the same temperature (thermal equilibrium).
Electric Current, Potential Difference and Electric Circuits – Electric current is the rate of flow of charge, I = Q/t, measured in amperes with an ammeter joined in series. Potential difference is the work done to move a unit charge between two points, V = W/Q, measured in volts with a voltmeter joined in parallel. Charge flows only in a closed circuit.

4. Interaction

Simple kinematics · Forces as agents of change · Newton's laws · Gravitational, electric and magnetic phenomena

Motion: Distance, Speed, Velocity, Acceleration and Graphs – An object is in motion when its position changes with time. Distance is the full path length (a scalar); displacement is the straight gap from start to finish with a direction (a vector). Speed = distance ÷ time; velocity = displacement ÷ time. Acceleration = change in velocity ÷ time. The slope of an s–t graph gives velocity, the slope of a v–t graph gives acceleration, and the area under a v–t graph gives the distance. For uniform acceleration: v = u + at, s = ut + ½at², v² = u² + 2as.
Forces: Pushes and Pulls – A force is a push or a pull between two objects. It is measured in newtons (N). Contact forces need touching (push, friction, normal force, tension, buoyancy); non-contact forces act at a distance (gravity, magnetism, electric). A force is drawn as an arrow: start = point of application, direction, length = size. Forces can change an object's speed, direction or shape. If forces balance, a still object stays still (equilibrium). Forces always come in pairs: if A pushes B, B pushes A back equally (Newton's third law).
Force and Laws of Motion – A force is a push or a pull. Balanced forces (net force zero) do not change motion; an unbalanced force changes speed or direction. Friction opposes sliding. First law: a body keeps its state of rest or uniform motion unless an unbalanced force acts (inertia; heavier bodies have more inertia). Momentum p = mv. Second law: F = ma (rate of change of momentum), 1 N = 1 kg m/s². Third law: forces come in equal and opposite pairs acting on two different bodies. For a system with no outside force, internal forces cancel and total momentum is conserved.
Fields and Forces – Some forces need touch, like a push with your hand. Others act across empty space: gravity, the electric force and the magnetic force. We explain these with a field: a region around an object where another object feels a force. Mass makes a gravitational field, charge makes an electric field, and magnets or currents make a magnetic field. We draw fields with field lines: the arrow shows the direction of force, and lines close together mean a strong field. Gravity and electric force get weaker with distance by the inverse-square law: double the distance, one quarter of the force. Fields also store energy. All forces in nature come from four fundamental forces: gravity, electromagnetism, the strong force and the weak force.

5. Change

Changes in material systems · Chemical reactions · Conservation of mass and definite proportions · Factors affecting reactions

Physical and Chemical Changes – In a physical change, a substance changes its shape, size or state, but no new substance forms; the particles stay the same. In a chemical change, the atoms rearrange to make one or more new substances with new properties. Signs include gas, colour change, heat or light, a precipitate and a new smell. In both kinds, the total mass stays the same.
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.
The Law of Conservation of Mass – In a chemical reaction, mass is not made and not destroyed. The total mass of the substances before the reaction equals the total mass after it. This is true because atoms are only rearranged: the same atoms, in the same numbers, are there before and after. If a gas leaves or joins from the air, the mass on a balance seems to change, but when we count every substance, the total stays the same. A related rule, the law of definite proportions, says a pure compound always has its elements in the same mass ratio (water is always 1 g hydrogen to 8 g oxygen).
Rates of Reaction – The rate of a reaction is how fast reactants are used up or products are made. Rate = change in amount ÷ time. Particles must collide with at least the activation energy to react. More frequent, more energetic collisions mean a faster rate. Raising concentration (or gas pressure), temperature or surface area, or adding a catalyst, makes reactions faster. A catalyst gives a path with lower activation energy and is not used up.